Phosphor particle coating

Abstract

The present invention provides a method for providing luminescent particles (100) having a hybrid coating, the method comprising: (i) providing a luminescent core (102) comprising a primer layer (105) on the luminescent core (102); (ii) providing a primary ALD coating (120) on the primer layer (105) by applying a primary atomic layer deposition process, the primary ALD coating (120) comprising a multi-layer (1120) having two or more layers (1121), the two or more layers (1121) having different chemical compositions, and wherein in the primary atomic layer deposition process, the metal oxide precursor is selected from the group of metal oxide precursors comprising Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V; (iii) providing a primary sol-gel coating (130) on the primary ALD coating (120) by applying a primary sol-gel coating process, the primary sol-gel coating (130) having a chemical composition different from one or more layers (1121) in the multi-layer (1120).

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to U.S. Application No. 16 / 915,422, titled "Phosphor Particle Coating", filed on June 29, 2020, and European Application No. 20189538.0, titled "Phosphor Particle Coating", filed on August 5, 2020. The said applications are incorporated herein by reference in their entireties. Technical field

[0003] The present invention relates to a method for providing a coated luminescent material, such a luminescent material, and an illumination device comprising such a luminescent material for wavelength conversion. Background art

[0004] Coating of luminescent materials is known in the art. For example, WO2014128676 describes coated luminescent particles, luminescent converter elements, light sources, illuminators, and methods for manufacturing coated luminescent particles. The coated luminescent particles comprise luminescent particles, a first coating, and a second coating. The luminescent particles comprise a luminescent material for absorbing light in a first spectral range and converting the absorbed light into light in a second spectral range. The luminescent material is sensitive to water. The first coating forms a first barrier layer against water and comprises a metal oxide or nitride, phosphide, sulfide - based coating. The second coating forms a second barrier layer against water and comprises a silicon - based polymer or a continuous layer comprising one of the materials AlPO 4 , SiO 2 , Al 2 O 3 and LaPO 4 The first coating and the second coating are light - transmissive. The first coating encapsulates the luminescent particles, and the second coating encapsulates the luminescent particles with the first coating. Summary of the invention

[0005] A moisture - sensitive luminescent powder material can be coated with a layer of amorphous or glassy material to reduce the decomposition rate due to moisture erosion. The coating can be applied by reacting dissolved inorganic precursors in a suspension (e.g., by sol - gel method) or by vapor deposition (e.g., chemical vapor deposition or atomic layer deposition (ALD) method) to deposit the material on the particle surface.

[0006] Atomic layer deposition may be a suitable method for depositing thin conformal coatings of various inorganic materials on powder particles. The ALD layer can be very dense and conformal and can be substantially impermeable to gases such as water vapor and oxygen.

[0007] The ALD process also allows for the deposition of multiple thin layers (nano-laminates) of different inorganic materials, each thin layer providing physical properties (such as moisture resistance, light transmittance, stress resistance, elasticity, etc.) to the layer, and these physical properties may be different for different (nano) layers.

[0008] The sol-gel process can be suitable for providing a (relatively) thick layer that can provide mechanical protection to the material coated with this layer.

[0009] Known coated luminescent particles may exhibit one or more drawbacks, such as decomposition of the luminescent material due to moisture or solvents, degradation due to high temperatures, and mechanical instability during handling of the luminescent particles. In addition, many known coating processes also have one or more drawbacks, such as agglomeration, reduced quantum efficiency of the coated luminescent material (compared to the uncoated material), and non-conformal coatings.

[0010] It seems that for the sol-gel coating process, only the properties of the luminescent material may not be sufficient. In addition, moisture-sensitive luminescent particles containing only an ALD coating may also be non-durable when exposed to mechanical stress. Further, it appears that moisture-sensitive luminescent particles having a sol-gel coating combined with an ALD coating disposed on top of the sol-gel coating can provide luminescent particles with a reduced decomposition rate due to the ingress of moisture under relatively harsh conditions (such as at a temperature of up to 60 °C and a relative humidity of 90%). However, for higher temperatures, such as those that may be generated in high-power LED applications (such as in flashlights and motor vehicle applications), alternative coating structures may be required. In addition, the ALD layer seems to exhibit an inherent (tensile) stress that can increase with an increase in layer thickness. The ALD coating can preferably be provided as a thin layer. However, it seems that the deposition of particularly thin ALD layers may be sensitive to surface contamination. Possible contamination of the surface of the particles to be coated may result in pinholes or other irregularities in the (thin) ALD layer.

[0011] Accordingly, one aspect of the present invention is to provide an alternative coating process that preferably further at least partially eliminates one or more of the above-mentioned drawbacks. Another aspect of the present invention is to provide an alternative luminescent material that preferably further at least partially eliminates one or more of the above-mentioned drawbacks. In yet another aspect, the present invention provides an illumination device including a luminescent material that preferably further at least partially eliminates one or more of the above-mentioned drawbacks.

[0012] The object of the present invention may be to overcome or improve at least one drawback of the prior art, or to provide a useful alternative.

[0013] Among other things, the present invention provides, in an embodiment, a coating structure that includes at least two layers, particularly at least three layers disposed around a luminescent core. Different layers can be selected based on having different functions. The coating structure can particularly include a primer layer, a coating provided by atomic layer deposition ("ALD coating"), and a coating provided by a sol-gel (deposition) process ("sol-gel coating"). The primer layer can promote good adhesion between surfaces and facilitate the deposition of a thin ALD coating. The ALD coating can protect the luminescent core from unwanted gases such as water vapor and oxygen or other chemical substances. The sol-gel coating can provide mechanical protection for the luminescent core and the ALD coating.

[0014] Accordingly, a hybrid coating method for a luminescent powder material is provided herein, the method including depositing a coating on a primer layer (on the surface of the luminescent core) by applying an ALD process and continuously depositing a sol-gel layer by applying a sol-gel type process to obtain uniformly coated luminescent particles. Using this method, luminescent particles with a hybrid coating can be provided.

[0015] Accordingly, in a first aspect, the present invention provides a method for providing a hybrid coating for luminescent particles. In an embodiment, the method particularly includes the following stages: (i) providing a luminescent core ("core") that includes a primer layer ("primer coating" or "primer coated layer") (or "primer layer including the luminescent core") on the luminescent core. The method further includes: (ii) providing a (main) atomic layer deposition coating ("(main) ALD coated layer" or "(main) ALD coating" or "(main) ALD layer") on the primer layer. In an embodiment, the (main) ALD coating is particularly provided on the primer layer including the luminescent core. The method further includes: (iii) providing a (main) sol-gel coated layer ("main" sol-gel coating" or "(main) sol-gel layer") on the (main) ALD coating. Additionally, the (main) ALD coating can be provided on the primer layer by applying a (main) atomic layer deposition process ("(main) ALD process"). Further, in a specific embodiment, the (main) ALD coating can include a multi-layer (or "stack") having two or more layers of different chemical compositions. In another specific embodiment, in the (main) atomic layer deposition process, the metal oxide precursor is selected from the group of metal oxide precursors including Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V (and optionally Si). The (main) sol-gel coating is particularly provided on the (main) ALD coating by applying a (main) sol-gel coating process. In another embodiment, the main sol-gel coating can have a chemical composition different from one or more of the layers in the multi-layer.

[0016] In yet another aspect, the present invention also provides a luminescent material comprising luminescent particles obtained by this method. In particular, in yet another aspect, the present invention provides a luminescent material comprising luminescent particles, wherein the luminescent particles comprise a luminescent core, the luminescent core comprising a primer layer on the luminescent core, in particular wherein the primer layer has a primer layer thickness (d1) of 0.1 - 10 nm, in particular 0.1 - 7 nm, such as 0.1 - 5 nm or 0.1 - 4 nm, and wherein the primer layer has a chemical composition different from that of the core; a (main) ALD (i.e., atomic layer deposition) coating, in particular comprising a multi-layer having two or more layers of different chemical compositions, wherein, in an embodiment, the (main) ALD coating has a (main) ALD coating thickness (d2) in the range of 5 - 250 nm, such as 5 - 100 nm, particularly 5 - 50 nm, such as particularly 10 - 50 nm, even more particularly 20 - 50 nm, and in particular wherein the multi-layer comprises one or more layers, the one or more layers comprising one or more oxides of Al, Zn Ta, Zr, Ti, Sn, Nb, Y, Ga and V (and optionally Si), wherein one or more of the two or more layers in the multi-layer has a chemical composition different from that of the primer layer, and furthermore, in an embodiment, particularly comprises a (main) sol-gel coating, wherein, in an embodiment, the (main) sol-gel coating has a (main) sol-gel coating thickness (d3) in the range of 50 - 700 nm, such as 50 - 600 nm, particularly 75 - 500 nm, such as particularly 100 - 500 nm. In a further embodiment, the (main) sol-gel coating has a chemical composition different from that of the (main) ALD coating, in particular different from one or more of the two or more layers in the multi-layer. Furthermore, in particular, the (main) ALD coating is disposed between the primer layer and the (main) sol-gel layer.

[0017] The present invention can provide luminescent particles and luminescent materials, i.e., luminescent materials comprising these (hybrid-coated) particles, which exhibit a significantly reduced decomposition rate due to moisture ingress. The coating of the luminescent particles can exhibit improved moisture resistance. The coating can further provide improved chemical and mechanical stability, allowing the integration of luminescent particles (phosphors), especially moisture-sensitive luminescent particles (phosphors), in high-power products, such as flashlights and motor vehicle applications that are subjected to high stress conditions (e.g., a working temperature of up to 85 °C, at high relative humidity (above 80% relative humidity)). With such a luminescent material, a relatively stable luminescent material is provided, the quantum efficiency of which is close to or equal to that of the original (uncoated) luminescent material, and which has very high stability against water and / or (humid) air, and is superior to uncoated or non-hybrid-coated luminescent particles.

[0018] In an embodiment, the present invention may particularly provide a method for providing a hybrid coating for luminescent particles, the method comprising: (i) providing a luminescent core, the luminescent core comprising a primer layer on the luminescent core; (ii) providing a primary ALD coating on the primer layer by applying a primary atomic layer deposition process, the primary ALD coating comprising a multi-layer having two or more layers with different chemical compositions, and wherein in the primary atomic layer deposition process, the metal oxide precursor is selected from the group of metal oxide precursors comprising Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V (and optionally Si); (iii) providing a primary sol-gel coating on the primary ALD coating by applying a primary sol-gel coating process, the primary sol-gel coating having a chemical composition different from one or more layers in the multi-layer. In particular, in the primary atomic layer deposition process, the metal oxide precursor is selected from the group of metal oxide precursors of metals selected from Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V (and optionally Si).

[0019] Thus, the starting material is a particulate luminescent material or a luminescent material made into particles. In addition, in particular, the luminescent core is a particulate core or a luminescent (core) material made into particles. The core can essentially be the (original) luminescent particle / nucleus, i.e., an uncoated / untreated luminescent particle. The luminescent particles (especially the core) of the particulate luminescent material are coated as described herein. The terms "luminescent particle", "luminescent core" and similar terms mean that the particle and / or nucleus emits light upon excitation by, in particular, UV and / or blue radiation (source radiation, see below). Here, the term "luminescent particle" can also be used to refer to the "luminescent core". In addition, in this document, the coated luminescent particles can also be referred to as "luminescent particles". It will be clear from the context whether the term "luminescent particle" refers to an uncoated nucleus, or for example whether it refers to a luminescent particle comprising a hybrid coating, or a luminescent particle comprising only one or more layers of the hybrid coating.

[0020] The luminescent core (before applying the ALD coating process) particularly comprises a primer layer on the surface of the luminescent core. In this document, the luminescent core comprising a primer layer (on the luminescent core) is also referred to as "luminescent core comprising a primer layer". In an embodiment, the original (core) material already comprises a primer layer. In an embodiment, for example, the core can comprise an oxide-containing surface. In a further embodiment, the primer layer can be provided to the original (core) material, particularly by the method of the present invention. Thus, in a further embodiment, the method can comprise providing a primer layer on the core (to provide a luminescent core comprising a primer layer on the luminescent core) (see further below).

[0021] The primer layer does not necessarily conform exactly to the core. The primer layer can be distributed particularly evenly over the surface of the luminescent core. However, in embodiments, the primer layer may not completely cover the surface of the core. In embodiments, the primer layer can cover at least 50%, particularly at least 75%, such as at least 90%, or particularly at least 95%, or even more particularly at least 99% of the core surface (see further below). The primer layer can be configured particularly to facilitate the deposition of the main ALD coating. The primer layer can act as a nucleation or seed layer for the main ALD coating.

[0022] The main ALD coating is disposed on the primer layer. Thus, in embodiments, the ALD coating can contact the surface of the luminescent core at a first location of the luminescent core that includes the primer layer, and the ALD coating can contact the primer layer at additional locations. The main ALD coating can optionally include multiple layers. However, the multiple layers of the main ALD coating are all ALD layers. Thus, this layer is referred to as the (main) ALD (coated) layer (and thus optionally includes an ALD multi-layer). In particular, the main ALD coating includes a multi-layer having two or more layers (with different chemical compositions), also see below. The main ALD coating particularly includes at least one or more alumina (especially Al 2 O 3 ) coatings.

[0023] Similarly, the main sol-gel coating can optionally include multiple layers. However, the (multi) layers of the main sol-gel coating are all sol-gel layers. Thus, this coating is also referred to in this document as the (main) sol-gel (coated) layer (and thus optionally includes a sol-gel multi-layer). Additionally, in particular, the main sol-gel coating is disposed on the main ALD coating without an intermediate layer. The main sol-gel coating particularly contains silica (especially SiO 2 ). Examples of multi-layers can include, for example, SiO 2 -Al 2 O 3-x (OH) 2x (sol-gel) multi-layers (where 0 ≤ x ≤ 3), such as a stack of three or more (sol-gel) layers, where SiO 2 and Al 2 O 3-x (OH) 2x (where 0 ≤ x ≤ 3) alternate. Optionally, another coating can be provided on the main sol-gel coating (see further below).

[0024] In particular, both the main ALD coating and the main sol-gel coating independently contain metal oxides, although hydroxides can also optionally be included in one or more of these layers. Additionally, independently, the main ALD coating and the main sol-gel coating can include mixed oxide layers. Further, as is known in the art, the coatings do not have to be completely stoichiometric oxides.

[0025] In an embodiment, the primer layer also includes a sol-gel coating provided by applying a sol-gel process. In the present context, such a sol-gel coating may be denoted as the primary sol-gel coating, especially for the purpose of distinguishing it from the main sol-gel coating. In an embodiment, the primary sol-gel coating may comprise a metal oxide and optionally a hydroxide, as described herein with respect to the main sol-gel coating. Additionally, in particular, the primary sol-gel coating may be provided as described with respect to the main sol-gel coating, also see below which further describes the sol-gel process. The primary sol-gel coating may in particular be provided as described with respect to the main sol-gel coating (and include the composition).

[0026] In a further embodiment, the primer layer may further include an oxide-containing layer. In a specific embodiment, the oxide-containing layer is provided by applying a chemical washing process on the luminescent core (see further below). The chemical washing process can in particular provide a washing result layer on the luminescent core. Thus, in an embodiment, the washing result layer includes the oxide-containing layer. The primer layer can in particular be used as a nucleation layer or a seed layer for the main ALD coating. However, for various embodiments, the primer layer may be structurally different. As described above, in an embodiment, the primer layer includes an oxide-containing layer (or an oxide-rich layer) on the surface of the luminescent core, especially consisting thereof. In a further embodiment, the primer layer includes the washing result layer, especially consisting of the washing result layer. In a further embodiment, the primer layer includes the primary sol-gel coating, especially consisting of the primary sol-gel coating. In a further specific embodiment, the primer layer includes the washing result layer and the primary sol layer.

[0027] In particular (if the core is subjected to a chemical washing process), the primary sol-gel coating is provided after the chemical washing process, and in particular the primary sol-gel coating may be provided on the washing result layer (especially the oxide-containing layer). However, in such an embodiment, the primary sol-gel coating may contact the washing result layer at a first location of the luminescent core. The primary sol-gel coating may contact the surface of the luminescent core at other locations of the luminescent core. Thus, in an embodiment, the primer layer includes an oxide-containing layer and a primary sol-gel layer, especially where the oxide-containing layer is arranged on the surface of the core (and at least a part of the primary sol-gel coating is arranged on the oxide-containing layer).

[0028] As described above, in embodiments, the position of the core may not be covered by the primary layer (in particular one or more oxide layers and the primary sol-gel coating). Thus, in embodiments, the main ALD coating may (be provided to) contact the primary sol-gel coating at some positions of the luminescent core, and the main ALD coating may (be provided to) contact the surface of the core at some other positions of the luminescent particle. In yet additional embodiments, the main ALD coating may (also) (be provided to) contact the washing result layer at some additional positions of the luminescent particle.

[0029] Typically, the thickness of the primer layer is less than the thickness of the main sol-gel layer and in particular also less than the thickness of the main ALD coating. Further, in particular the thickness of the main sol-gel coating is typically greater than the thickness of the ALD coating. The thickness of the primer layer is in particular equal to or less than 10 nm, for example equal to or less than 7 nm, in particular equal to or less than 5 nm, and even more in particular equal to or less than 4 nm. In embodiments, the thickness of the primer layer may be at least 0.1 nm, for example at least 0.2 nm, in particular at least 0.5 nm, for example in particular at least 1 nm. The thickness of the primary layer may in particular be the result of the thickness of the primary sol-gel coating. Thus, in particular the primary sol-gel coating may be equal to or less than 10 nm, for example equal to or less than 7 nm, in particular equal to or less than 5 nm, for example equal to or less than 4 nm. In embodiments, the oxide layer may be less than 1 nm thick. In embodiments, the primer layer has a primer layer thickness (d1) in the range of 0.1 - 5 nm. In additional embodiments, the primer layer comprises a primary sol-gel layer provided by applying a primary sol-gel coating process. The thickness of the main sol-gel coating may be at least 10 times, for example at least 50 times, in particular at least 100 times the thickness of the primary layer.

[0030] Further, in particular the thickness of the main sol-gel coating is typically greater than the thickness of the main ALD coating, for example at least 1.2 times (greater than the thickness of the main ALD coating), such as at least 1.5 times, such as at least 2 times, or even at least 4 times or at least 5 times or at least 10 times.

[0031] In a specific embodiment, the method of the present invention comprises (i) providing a primer layer on the core, in particular a primer layer having a primer layer thickness (d1) in the range of 0.1 - 10 nm, in particular 0.1 - 7 nm, for example 0.1 - 5 nm or 0.1 - 4 nm (to provide a primer layer comprising a luminescent core); (ii) providing a main ALD coating on the primer layer (in particular on the primer layer comprising the luminescent core) by applying a main atomic layer deposition process, the main ALD coating having a main ALD coating thickness (d2) in the range of 3 - 250 nm, for example 5 - 250 nm, in particular 5 - 100 nm, even more particularly 5 - 50 nm, for example in particular 10 - 50 nm, even more particularly 20 - 50 nm; and in particular (iii) providing a main sol - gel coating on the main ALD coating by applying a main sol - gel process, the main sol - gel coating having a main sol - gel coating thickness (d3) in the range of 50 - 700 nm, for example 50 - 600 nm, in particular 75 - 500 nm, for example in particular 100 - 500 nm.

[0032] In particular, the primer layer has a primer layer thickness (d1) in the range of 0.1 - 10 nm, in particular 0.1 - 7 nm, for example 0.1 - 5 nm or 0.1 - 4 nm. Furthermore, in particular, the main ALD coating has a main ALD coating thickness (d2) in the range of 3 - 250 nm, for example 5 - 250 nm, in particular 5 - 100 nm, even more particularly 5 - 50 nm, for example in particular 10 - 50 nm, even more particularly 20 - 50 nm. In particular, the main sol - gel coating has a main sol - gel coating thickness (d3) in the range of 50 - 700 nm, for example 50 - 600 nm, in particular 75 - 500 nm, for example in particular 100 - 500 nm.

[0033] Thus, as described above, the luminescent particles in the embodiment comprise: a luminescent core; a primer layer having a primer layer thickness (d1) in the range of 0.1 - 10 nm, particularly 0.1 - 7 nm, for example 0.1 - 5 nm or 0.1 - 4 nm; a main ALD coating having a main ALD coating thickness (d2) in the range of 3 - 250 nm, for example 5 - 250 nm, particularly 5 - 100 nm, even more particularly 5 - 50 nm, for example particularly 10 - 50 nm, even more particularly 20 - 50 nm; and a main sol - gel coating having a main sol - gel coating thickness (d3) in the range of 50 - 700 nm, for example 50 - 600 nm, particularly 75 - 500 nm, for example particularly 100 - 500 nm.

[0034] In an embodiment, the primer layer at least partially encapsulates the surface of the luminescent core. In a further embodiment, the main ALD coating encapsulates the primer layer. In a further embodiment, the main sol-gel coating encapsulates the main ALD coating. In yet another embodiment, another ALD coating encapsulates the main sol-gel coating (see below). Thus, the hybrid coating may comprise a main ALD coating and a main sol-gel coating, in particular a primer layer, a main ALD coating and a main sol-gel coating. The primer layer is particularly disposed between the surface of the luminescent core and the main ALD coating. The main ALD coating is particularly disposed between the main sol-gel coating and the primer layer.

[0035] In yet a further embodiment, the luminescent particles may comprise an additional coating disposed on the main sol-gel coating. In a further embodiment, the hybrid coating further comprises an additional coating disposed at the main sol-gel coating. The additional coating may particularly comprise another ALD coating, which particularly encapsulates the main sol-gel coating. Thus, in an embodiment, the luminescent particles (further) comprise another ALD coating disposed on the main sol-gel coating. The another ALD coating particularly has another ALD coating thickness (d4) in the range of 1 - 100 nm, such as 5 - 75 nm, in particular 10 - 75 nm, such as particularly 10 - 50 nm. In addition, in particular, the another ALD coating has a chemical composition different from that of the main sol-gel coating.

[0036] Thus, in a specific embodiment, the method further comprises (iv) providing another ALD coating (particularly thereby providing another ALD-coated luminescent particle) on the main sol-gel coating by applying another atomic layer deposition process, in particular wherein the another ALD coating has another ALD coating thickness (d4) in the range of 1 - 100 nm, such as 5 - 75 nm, particularly 10 - 75 nm, such as particularly 10 - 50 nm, and in particular wherein the another ALD coating has a chemical composition different from that of the main sol-gel coating. The another ALD coating may be provided by the ALD process described herein, particularly with respect to the main ALD layer. The another ALD layer may (also) comprise multiple layers. The another ALD layer may further particularly comprise the components (and / or (metal) oxides) described with respect to the main ALD layer. In an embodiment, the another ALD coating comprises one or more oxides of one or more of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga and V and optionally Si.

[0037] Here, the term "thickness" is used with respect to coatings and layers. This term particularly relates to the average thickness of the coating over the entire surface coated by the corresponding layer. For example, the primary layer may not completely cover the surface of the core, and the (local) thickness of the primer layer may be substantially zero at the surface location of the core. At other locations on the surface, the maximum (local) thickness of the primer layer can be 3 nm. Then, for example, the thickness of the primer layer can be in the range greater than 0 and less than 3 nm. Additionally, if the (coated) layer completely covers the core or another coated layer, the local thickness may vary. In particular, for example, the sol-gel process can provide a coating with a slightly concave shape, or for example, can include one or more small pinholes. Thus, the layer thickness described herein is especially the average layer thickness. However, in particular, at least for the primer layer, the primary sol-gel coating, the primary ALD coating, and another ALD coating (when present), at least 50%, and even more particularly at least 80% of the area of each layer has this specified layer thickness. In particular, this indicates that such a thickness will be found under at least 50% of the area of the layer.

[0038] The luminescent core of interest can in principle include each type of (raw) luminescent particle or particulate material. However, of particular interest are those luminescent particulate materials (particles) that are less stable in air or water or a humid environment, such as, for example, (oxy)sulfides, (oxy)nitrides, etc. Thus, in embodiments, the luminescent core (and the luminescent particles including the luminescent core) includes one or more of nitride luminescent materials, oxynitride luminescent materials, halide luminescent materials, oxyhalide luminescent materials, sulfide luminescent materials, and oxysulfide luminescent materials. Additionally or alternatively, the luminescent core (luminescent particles) can include selenide luminescent materials. Thus, the term "luminescent core" (and "luminescent particles") can also refer to a combination of particulate materials of different types of luminescent materials. In embodiments, the luminescent core can particularly include multiple particulate luminescent materials / luminescent particles.

[0039] In a specific embodiment, the luminescent core (or the material of the luminescent core) can be selected from the group of the following luminescent material systems: MLiAl 3 N 4 :Eu (M = Sr, Ba, Ca, Mg), MLi 2 Al 2 O 2 N 2 :Eu (M = Ba, Sr, Ca), M 2 SiO 4 :Eu (M = Ba, Sr, Ca), MSe 1-x S x :Eu (M = Sr, Ca, Mg), MA 2 S 4 :Eu (M = Sr, Ca, A = Al, Ga), M2 SiF 6 :Mn (M = Na, K, Rb), MSiAlN 3 :Eu (M = Ca, Sr), M 8 Mg(SiO 4 ) 4 Cl 2 :Eu (M = Ca, Sr), M 3 MgSi 2 O 8 :Eu (M = Sr, Ba, Ca), MSi 2 O 2 N 2 :Eu (M = Ba, Sr, Ca), MLi 3 SiO 4 :Eu (M = Li, Na, K, Rb, Cs), M 2 Si 5-x Al x O x N 8-x :Eu (M = Sr, Ca, Ba). However, other systems may also be protected by the hybrid coating. Combinations of particles / microparticle materials of two or more different luminescent materials may also be applied, such as, for example, a combination of a green or yellow luminescent material and a red luminescent material.

[0040] As is known in the art, a term such as "M = Sr, Ba, Ca, Mg" means that M includes one or more of Sr, Ba, Ca, and Mg. For example, referring to MSiAlN 3 :Eu (M = Ca, Sr), this may refer, by way of example, to CaSiAlN 3 :Eu, or SrSiAlN 3 :Eu, or Ca 0.8 Sr 0.2 SiAlN 3 :Eu, and so on. In addition, the chemical formula "MLiAl 3 N 4 :Eu (M = Sr, Ba, Ca, Mg)" is equivalent to the chemical formula (Sr,Ba,Ca,Mg)LiAl 3 N 4 :Eu. In addition, for clarity, the chemical formula "(M1)LiAl 3 N 4 :Eu, where M1 = Sr, Ba, Ca" etc. may also be used, for example when representing more than one group with different elements, such as in a case like "where the luminescent material is selected from (M1)Li d Mg a Al b N 4: a group consisting of Eu, where 0 ≤ a ≤ 4, 0 ≤ b ≤ 4, 0 ≤ d ≤ 4, and M1 includes one or more of the group consisting of Ca, Sr, and Ba; and selected from the group consisting of (M2) Li 2 Al 2-z Si z O 2-z N 2+z : a group consisting of Eu, where 0 ≤ z ≤ 0.1, and M2 includes one or more of the group consisting of Sr and Ba”. In addition, M1, M2, etc. can also refer to one or more (corresponding) elements. In the example given above, for example, M1 can be Sr, Ba, or Ca in the embodiment. In another embodiment, M1 can be a combination of Sr and Ba, or for example, a combination of Sr and Ca, or a combination of Sr, Ba, and Ca, etc. In addition, these elements can exist in any proportion, for example, 20% Sr, 20% Ca, and 50% Ba, or 10% Ba and 90% Sr, etc. Similarly, this also applies to other formulations of the inorganic luminescent materials described herein.

[0041] In another specific embodiment, the luminescent core can be selected from the following group of luminescent material systems: M 1-x-y- z Z z A a B b C c D d E e N 4-n O n :ES x ,RE y, where M is selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium); Z is selected from the group consisting of monovalent Na (sodium), K (potassium), and Rb (rubidium); A is selected from the group consisting of divalent Mg (magnesium), Mn (manganese), Zn (zinc), and Cd (cadmium), in particular, A is selected from the group consisting of divalent Mg (magnesium), Mn (manganese), and Zn (zinc), and even more particularly is selected from the group consisting of divalent Mg (magnesium) and Mn (manganese); B is selected from the group consisting of trivalent B (boron), Al (aluminum), and Ga (gallium); C is selected from the group consisting of tetravalent Si (silicon), Ge (germanium), Ti (titanium), and Hf (hafnium); D is selected from the group consisting of monovalent Li (lithium) and Cu (copper); E is selected from the group consisting of P (elemental phosphorus), V (vanadium), Nb (niobium), and Ta (tantalum); ES is selected from the group consisting of divalent Eu (europium), Sm (samarium), and ytterbium, especially selected from the group consisting of divalent Eu and Sm; RE is selected from the group consisting of trivalent Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), and Tm (thulium); where 0 ≤ x ≤ 0.2; 0 ≤ y ≤ 0.2; 0 < x + y ≤ 0.4; 0 ≤ z < 1; 0 ≤ n ≤ 0.5; 0 ≤ a ≤ 4 (such as 2 ≤ a ≤ 3); 0 ≤ b ≤ 4; 0 ≤ c ≤ 4; 0 ≤ d ≤ 4; 0 ≤ e ≤ 4; a + b + c + d + e = 4; and 2a + 3b + 4c + d + 5e = 10 - y - n + z. In particular, z ≤ 0.9, such as z ≤ 0.5. Further, especially x + y + z ≤ 0.2.

[0042] The equations a + b + c + d + e = 4 and 2a + 3b + 4c + d + 5e = 10 - y - n + z specifically determine the Z, A, B, C, D, and E cations and the O and N anions in the lattice, and thus (also) define the charge neutrality of the system. For example, charge compensation is covered by the chemical formula 2a + 3b + 4c + d + 5e = 10 - y - n + z. It covers charge compensation, for example, by reducing the O content, or by replacing a C cation with a B cation or an A cation with a B cation, etc. For example: x = 0.01, y = 0.02, n = 0, a = 3; then 6 + 3b + 4c = 10 - 0.02; where a + b + c = 4: b = 0.02, c = 0.98.

[0043] As will be clear to those skilled in the art, a, b, c, d, e, n, x, y, z are always equal to or greater than zero. When a is defined in combination with the equations a + b + c + d + e = 4 and 2a + 3b + 4c + d + 5e = 10 - y - n + z, then in principle b, c, d, and e no longer need to be defined. However, for the sake of completeness, 0 ≤ b ≤ 4; 0 ≤ c ≤ 4; 0 ≤ d ≤ 4; 0 ≤ e ≤ 4 are also defined herein.

[0044] Assume a system such as SrMg 2 Ga 2 N 4 :Eu. Here, a = 2, b = 2, c = d = e = y = z = n = 0. In such a system, 2 + 2 + 0 + 0 + 0 = 4 and 2*2 + 3*2 + 0 + 0 + 0 = 10–0–0+0 = 10. Thus, both equations are satisfied. Assume that 0.5O is introduced. A system with 0.5O can be obtained, for example, when 0.5Ga-N is replaced by 0.5Mg-O (which is a charge-neutral substitution). This will result in SrMg 2.5 Ga 1.5 N 3.5 O 0.5 :Eu. Here, in such a system 2.5 + 1.5 + 0 + 0 + 0 = 4 and 2*2.5 + 3*1.5 + 0 + 0 + 0 = 10-0-0.5+0 = 9.5. Thus, this also satisfies both equations.

[0045] As indicated above, in a preferred embodiment, d > 0 and / or z > 0, especially at least d > 0. In particular, the phosphor comprises at least lithium. In yet another embodiment, 2 ≤ a ≤ 3, and especially also d = 0, e = 0, and z = 0. In such an example, the phosphor is characterized, among other things, by a + b + c = 4; and 2a + 3b + 4c = 10 - y – n.

[0046] In a further specific embodiment that can be combined with the foregoing embodiments, e = 0. In yet another further specific embodiment that can be combined with the foregoing embodiments, M is Ca and / or Sr.

[0047] Thus, in a specific embodiment, the phosphor has the chemical formula M(Ca and / or Sr) 1-x-y Mg a Al b Si c N 4-n O n :ES x ,RE y(I), where ES is selected from the group consisting of divalent Eu (europium), Sm (samarium), or Yb (ytterbium); RE is selected from the group consisting of trivalent Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), and Tm (thulium), where y / x < 0.1, especially < 0.01, and n ≤ 0.1, especially < 0.01, even more especially < 0.001, still even more especially < 0.0001. Thus, in this embodiment, a phosphor substantially containing samarium and / or europium is described. For example, when divalent Eu is present, where x = 0.05, and for example, y1 of Pr can be 0.001, and y2 of Tb can be 0.001, resulting in y = y1 + y2 = 0.002. In such an example, y / x = 0.04. Even more particularly, y = 0. However, as indicated elsewhere, when applying Eu and Ce, the ratio y / x can be greater than 0.1.

[0048] The condition 0 < x + y ≤ 0.4 indicates that M can be replaced by up to 40% in total of ES and / or RE. The condition "0 < x + y ≤ 0.4" combined with the combination of x and y between 0 and 0.2 indicates the presence of at least one of ES and RE. It is not necessary for both types to be present. As indicated above, both ES and RE can each individually refer to one or more subspecies, such as ES referring to one or more of Sm and Eu, and RE referring to one or more of Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm.

[0049] Especially when europium is applied as a divalent luminescent substance or dopant (i.e., Eu 2+ ), the molar ratio between samarium and europium (Sm / Eu) < 0.1, especially < 0.01, especially < 0.001. This also applies when europium is applied in combination with ytterbium. When europium is used as a divalent luminescent substance or dopant, the molar ratio between ytterbium and europium (Yb / Eu) < 0.1, especially < 0.01, especially < 0.001. If all three are applied together, the same molar ratio may apply, i.e., ((Sm + Yb) / Eu) < 0.1, especially < 0.01, especially < 0.001.

[0050] In particular, x is in the range of 0.001 - 0.2 (i.e., 0.001 ≤ x ≤ 0.2), such as 0.002 - 0.2, such as 0.005 - 0.1, especially 0.005 - 0.08. Especially in the case of divalent europium in the system described herein, the molar percentage can be in the range of 0.1 - 5% (0.001 ≤ x ≤ 0.05), such as 0.2 - 5%, such as 0.5 - 2%. For other luminescent ions, in the embodiment, x can (but not necessarily) be equal to or greater than 1% (x is equal to or greater than 0.01).

[0051] In a specific embodiment, the phosphor is selected from the group consisting of (Sr,Ca)Mg 3 SiN 4 :Eu, (Sr,Ca)Mg 2 Al 2 N 4 :Eu, (Sr,Ca)LiAl 3 N 4 :Eu and (Sr,Ca)Li d Mg a Al b N 4 :Eu, where a, b, d are defined as above.

[0052] Also as indicated herein, the symbol "(Sr,Ca)" and similar symbols with other elements indicate that the M-position is occupied by Sr and / or Ca cations (or other elements respectively).

[0053] In another specific embodiment, the phosphor is selected from the group consisting of Ba 0.95 Sr 0.05 Mg 2 Ga 2 N 4 :Eu, BaMg 2 Ga 2 N 4 :Eu, SrMg 3 SiN 4 :Eu, SrMg 2 Al 2 N 4 :Eu, SrMg 2 Ga 2 N 4 :Eu, BaMg 3 SiN 4 :Eu, CaLiAl 3 N 4 :Eu, SrLiAl 3 N 4 :Eu, CaLi 0.5 MgAl 2.5 N 4 :Eu, and SrLi 0.5 MgAl 2.5 N 4 :Eu. Another (non-limiting) example of such a phosphor is, for example, (Sr 0.8 Ca 0.2 ) 0.995 LiAl 2.91 Mg 0.09 N 3.91 O0.09 : Eu 0.005 ; (Sr 0.9 Ca 0.1 ) 0.905 LiAl 3 N 3.91 O 0.09 : Eu 0.005 ; (Sr 0.8 Ca 0.03 Ba 0.17 ) 0.989 LiAl 2.99 Mg 0.01 N 4 : Ce 0.01 , Eu 0.001 ; Ca 0.995 LiAl 2.995 Mg 0.005 N 3.99 5 O 0.005 : Yb 0.005 (YB(II)); Na 0.995 MgAl 3 N 4 : Eu 0.005 ; Na 0.895 Ca 0.1 Mg 0.9 Li 0.1 Al 3 N 4 : Eu 0.005 ; Sr 0.99 LiMgAlSiN 4 : Eu 0.01 ; Ca 0.995 LiAl 2.955 Mg 0.045 N 3.96 O 0.04 : Ce 0.005 ; (Sr 0.9 Ca 0.1 ) 0.998 Al 1.99 Mg 2.01 N 3.99 O 0.01 : Eu 0.002 ; (Sr 0.9 Ba 0.1 ) 0.998 Al 1.99 Mg 2.01 N 3.99 O 0.01 : Eu 0.002 .

[0054] In additional specific embodiments, the phosphor is selected from (Sr,Ca)Mg3 SiN 4 : Eu and (Sr,Ca)Mg 2 Al 2 N 4 : Eu, and the group consisting of Ba 0.95 Sr 0.05 Mg 2 Ga 2 N 4 : Eu, BaMg 2 Ga 2 N 4 : Eu, SrMg 3 SiN 4 : Eu, SrMg 2 Al 2 N 4 : Eu, SrMg 2 Ga 2 N 4 : Eu and BaMg 3 SiN 4 : Eu, and even more particularly (Sr,Ca)Mg 3 SiN 4 : Eu and (Sr,Ca)Mg 2 Al 2 N 4 : Eu - can be phosphors with good luminescent properties.

[0055] In a further specific embodiment, the phosphor (especially the luminescent material) is selected from the group consisting of (Sr,Ca)LiAl 3 N 4 : Eu and (Sr,Ca,Ba)Li d Mg a Al b N 4 : Eu, where 0 ≤ a ≤ 4, 0 ≤ b ≤ 4, 0 ≤ d ≤ 4; and a + b + d = 4 and 2a + 3b + d = 10. In yet another specific embodiment, the phosphor is selected from (Sr,Ba)Li 2 Al 2-z Si z O 2-z N 2+z : Eu, where 0 ≤ z ≤ 0.1.

[0056] In an embodiment, the luminescent material is selected from the group of SrLiAl 3 N 4 : Eu. The luminescent material can for example include SrLiAl 3 N4 : Eu, where the doping concentration of Eu ranges from 0.1 - 5%, especially 0.1 - 2%, for example 0.2 - 1.2% relative to Sr.

[0057] In a further specific embodiment, the phosphor / luminescent core (luminescent material) contains SrLi 2 Al 1.995 Si 0.005 O 1.995 N 2.005 :Eu 2+ , especially where the doping concentration of Eu ranges from 0.1 - 5%, especially 0.1 - 2%, 0.2 - 1.5% relative to Sr.

[0058] Particularly interesting are phosphors where the phosphor satisfies 0 ≤ x ≤ 0.2, y / x < 0.1, M includes at least Sr, z ≤ 0.1, a ≤ 0.4, 2.5 ≤ b ≤ 3.5, B includes at least Al, c ≤ 0.4, 0.5 ≤ d ≤ 1.5, D includes at least Li, e ≤ 0.4, n ≤ 0.1, and where ES includes at least Eu. In particular, y + z ≤ 0.1. Further, especially x + y + z ≤ 0.2. Further, especially a is close to 0 or zero. Further, especially b is about 3. Further, especially c is close to 0 or zero. Further, especially d is about 1. Further, especially e is close to 0 or zero. Further, especially n is close to 0 or zero. Further, especially y is close to 0 or zero. In terms of quantum efficiency and hydrolysis stability, particularly good systems are those with z + d > 0, i.e., one or more of Na, K, Rb, Li, and Cu(I) are available, especially at least Li, such as for example (Sr,Ca)LiAl 3 N 4 :Eu and (Sr,Ca)Li d Mg a Al b N 4 :Eu, where a, b, d are as defined above. In a further specific embodiment, the phosphor is selected from the group consisting of CaLiAl 3 N 4 :Eu, SrLiAl 3 N 4 :Eu, CaLi 0.5 MgAl 2.5 N 4 :Eu, and SrLi 0.5 MgAl 2.5 N 4 :Eu. Further particularly interesting phosphors are (Sr,Ca,Ba)(Li,Cu)(Al,B,Ga) 3 N 4:Eu, which includes M ions (at least Sr), B ions (at least Al), and D ions (at least Li).

[0059] In an embodiment, the phosphor (luminescent core) is selected from the group consisting of (M1) Li d Mg a Al b N 4 :Eu, where 0 ≤ a ≤ 4, 0 ≤ b ≤ 4, 0 ≤ d ≤ 4, and M1 includes one or more elements selected from the group consisting of Ca, Sr, and Ba, and a + b + d = 4 and 2a + 3b + d = 10; and selected from the group consisting of (M2) Li 2 Al 2-z Si z O 2-z N 2+z :Eu, where 0 ≤ z ≤ 0.1, and M2 includes one or more elements selected from the group consisting of Sr and Ba.

[0060] Thus, in a particular embodiment, the luminescent particles include a luminescent material selected from SrLiAl 3 N 4 :Eu 2+ (category). The term "category" herein particularly refers to a group of materials having the same crystal structure. In addition, the term "category" may also include partial substitution of cations and / or anions. For example, in some of the above categories, Al - O can be partially replaced by Si - N (or vice versa). SrLiAl 3 N 4 :Eu 2+ 's category particularly may relate to a group of materials having the same crystal structure, especially where Sr is partially replaced by divalent Eu (e.g., 0.1% or 2%). For example, Sr 0.995 LiAl 3 N 4 :Eu 0.005 and Sr 0.98 LiAl 3 N 4 :Eu 0.02 are such elements. Similarly, SrLi 2 Al 1.995 Si 0.005 O 1.995 N 2.005 :Eu 2+ category (see also below) may, for example, include Sr 0.999 Li 2 Al 1.995 Si 0.005 O 1.995 N 2.005 :Eu 0.001and Sr 0.985 Li 2 Al 1.995 Si 0.005 O 1.995 N 2.005 :Eu 0.015 Optionally, a part of Sr can also be replaced by another alkaline earth metal (Group 2 element of the periodic table). SrLiAl is provided above 3 N 4 :Eu 2+ Examples of the category. However, other luminescent materials may also be possible.

[0061] In a further embodiment, the luminescent material (or phosphor) is selected from the group consisting of (Sr,Ca)LiAl 3 N 4 :Eu and (Sr,Ca,Ba)Li d Mg a Al b N 4 :Eu, where 0 ≤ a ≤ 4, 0 ≤ b ≤ 4, 0 ≤ d ≤ 4; and a + b + d = 4 and 2a + 3b + d = 10, and selected from (Sr,Ba)Li 2 Al 2-z Si z O 2-z N 2+z :Eu, where 0 ≤ z ≤ 0.1.

[0062] The luminescent core can thus particularly include phosphors. In addition, the luminescent core particularly contains the luminescent materials described herein, especially with respect to phosphors. The method can be applied to provide more than one, especially multiple, luminescent particles with a hybrid coating (and especially coating more than one luminescent core).

[0063] In a further embodiment of the luminescent material, the luminescent core comprises (phosphor) materials selected from the group consisting of: (i) (the) SrLiAl 3 N 4 :Eu 2+ (category), especially where the (Eu) doping concentration is in the range of 0.1 - 5%, especially 0.1 - 2%, even more especially 0.2 - 1.2%, relative to Sr, and (ii) (the) SrLi 2 Al 1.995 Si 0.005 O 1.995 N 2.005 :Eu 2+ , especially where the Eu doping concentration is in the range of 0.1 - 5%, especially 0.1 - 2%, even more especially 0.2 - 1.5 at%, relative to Sr. In addition, in particular, the third coating comprises SiO2 and one or more of the multiple layers contain Ta 2 O 5 、HfO 2 、TiO 2 and ZrO 2 one or more of them, and one or more (other) layers of the multiple layers contain Al 2 O 3 Specifically, the layer in contact with the main sol-gel coating here is composed of one or more metal oxides selected from the group of HfO 2 、ZrO 2 、TiO 2 、Ta 2 O 5 .

[0064] Such luminescent particles can have a number-average particle size in the range of 0.1 - 50 μm, for example in the range of 0.5 - 40 μm, for example especially in the range of 0.5 - 20 μm. Thus, the luminescent core can have a size of, for example, up to about 500 μm, for example up to about 100 μm, such as up to about 50 μm. Especially for larger particle sizes, basically only a single particle can be coated, resulting in a luminescent core size on the order of 50 μm or less. Thus, the present invention relates to the coating of particles. When nanoparticles or quantum dots are used as the basis for the particle luminescent material, the size of the luminescent core can be significantly smaller. In this case, the core can be less than about 1 μm or significantly smaller (also see the size of the QD below).

[0065] Alternatively or additionally, the (multiple) luminescent particles - in particular the (multiple) luminescent cores - comprise luminescent quantum dots. In an embodiment, the term "quantum dot" or "luminescent quantum dot" may also refer to a combination of different types of quantum dots, i.e. quantum dots with different spectral characteristics. QDs are also referred to herein as "wavelength converter nanoparticles" or "luminescent nanoparticles". The term "quantum dot" refers in particular to quantum dots that emit light in one or more of UV, visible light and IR when excited with suitable radiation, such as UV radiation. Quantum dots or luminescent nanoparticles (which are referred to herein as wavelength converter nanoparticles) may, for example, comprise II-VI compound semiconductor quantum dots selected from (a group consisting of core-shell quantum dots, wherein the core is selected from) a group consisting of: CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, Z nSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, Hg ZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe and HgZnSTe. In another embodiment, the luminescent nanoparticles may be, for example, III-V compound semiconductor quantum dots selected from (the group consisting of core-shell quantum dots, wherein the core is selected from) the group consisting of GaN, GaP, GaAs, AlN, AlP, AlAs, InN, InP, InGaP, InAs, GaNP, GaNAs, GaPAs, AlNAs, AlPAs, InNP, InNAs, InNAs, InPAs, GaAlNP, GaAlNAs, GaAlPAs, GaInNP, GaInNAs, GaInPAs, InAlNP, InAlNAs and InAlPAs. In yet another embodiment, the luminescent nanoparticles may be, for example, I-III-VI2 chalcopyrite semiconductor quantum dots selected from (the group consisting of core-shell quantum dots, wherein the core is selected from) the group consisting of CuInS 2 、CuInSe 2 、CuGaS 2 、CuGaSe 2 、AgInS 2 、AgInSe 2 、AgGaS 2 and AgGaSe 2。In yet another embodiment, the luminescent nanoparticles can be, for example, (core-shell quantum dots, where the core is selected from the group consisting of I-V-VI2 semiconductor quantum dots) I-V-VI2 semiconductor quantum dots, for example selected from the group consisting of (the group consisting of core-shell quantum dots, where the core is selected from) the following: LiAsSe 2 , NaAsSe 2 and KAsSe 2 。In yet another embodiment, the luminescent nanoparticles can be, for example, core-shell quantum dots, where the core is selected from the group consisting of group IV-VI compound semiconductor nanocrystals (such as SbTe). In a specific embodiment, the luminescent nanoparticles are selected from the group consisting of (the group consisting of core-shell quantum dots, where the core is selected from) the following: InP, CuInS 2 , CuInSe 2 , CdTe, CdSe, CdSeTe, AgInS 2 and AgInSe 2 。In yet another embodiment, the luminescent nanoparticles can be, for example, one of a group of core-shell quantum dots, where the core is selected from the group consisting of II-VI, III-V, I-III-V, and IV-VI compound semiconductor nanocrystals, which are selected from the materials described above having internal dopants (such as ZnSe:Mn, ZnS:Mn). The doping elements can be selected from Mn, Ag, Zn, Eu, S, P, Cu, Ce, Tb, Au, Pb, Tb, Sb, Sn, and Tl. Here, the luminescent material based on the luminescent nanoparticles can also include different types of QDs, such as CdSe and ZnSe:Mn. The luminescent core can include one or more, especially more (identical or different) (types) of luminescent nanoparticles.

[0066] Using group II-VI quantum dots seems to be particularly advantageous. Thus, in an embodiment, the semiconductor-based luminescent quantum dots include II-VI quantum dots, especially selected from the group consisting of core-shell quantum dots, where the core is selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, and HgZnSTe, and even more particularly selected from the group consisting of CdS, CdSe, CdSe / CdS, and CdSe / CdS / ZnS.

[0067] In an embodiment, the wavelength-converting nanoparticles have an average particle size in the range of from about 1 to about 1000 nanometers (nm), and preferably in the range of from about 1 to about 100 nm. In an embodiment, the average particle size of the nanoparticles is in the range of about 1 to about 20 nm. In an embodiment, the average particle size of the nanoparticles is in the range of about 1 to about 10 nm. The luminescent nanoparticles (without coating) can have dimensions in the range of about 2 - 50 nm, such as 2 - 20 nm, particularly 2 - 10 nm, and even more particularly 2 - 5 nm; in particular, at least 90% of the nanoparticles have dimensions within the indicated ranges (i.e., for example, at least 90% of the nanoparticles have dimensions in the range of 2 - 50 nm, or in particular at least 90% of the nanoparticles have dimensions in the range of 2 - 5 nm). The term "dimensions" particularly relates to one or more of length, width, and diameter, depending on the shape of the nanoparticles. Typical dots are made of binary alloys, such as cadmium selenide, cadmium sulfide, indium arsenide, and indium phosphide. However, the dots can also be made of ternary alloys, such as cadmium selenosulfide. These quantum dots can contain as few as 100 to 100,000 atoms within the quantum dot volume, with diameters of 10 to 50 atoms. This corresponds to about 2 to 10 nm. For example, spherical particles with a diameter of about 3 nm, such as CdSe, InP, or CuInSe 2 The luminescent nanoparticles (without coating) can have shapes such as spherical, cubic, rod-shaped, wire-shaped, disk-shaped, multi-pod-shaped, etc., where one-dimensional dimensions are less than 10 nm. For example, CdSe nanorods with a length of 20 nm and a diameter of 4 nm can be provided. Thus, in an embodiment, the semiconductor-based luminescent quantum dots include core-shell quantum dots. In a further embodiment, the semiconductor-based luminescent quantum dots include dot-in-rod nanoparticles. Combinations of different types of particles can also be applied. Here, the term "different types" can relate to different geometries as well as different types of semiconductor luminescent materials. Thus, combinations of two or more (as indicated above) quantum dots or luminescent nanoparticles can also be applied.

[0068] In an embodiment, the nanoparticles can include semiconductor nanocrystals that include a core containing a first semiconductor material and a shell containing a second semiconductor material, where the shell is disposed on at least a portion of the surface of the core. The semiconductor nanocrystals including a core and a shell are also referred to as "core / shell" semiconductor nanocrystals. Any of the materials indicated above can be particularly used as the core. Thus, the phrase "core-shell quantum dots, where the core is selected from the group consisting of" is applied to some of the quantum dot materials listed above. The term "core-shell" can also refer to "core-shell-shell", etc., which includes gradient alloy shells, or dot-in-rod, etc.

[0069] For example, a semiconductor nanocrystal can include a core having the chemical formula MX, where M can be cadmium, zinc, magnesium, mercury, aluminum, gallium, indium, thallium, or a mixture thereof, and X can be oxygen, sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, or a mixture thereof. Examples of materials suitable for use as the semiconductor nanocrystal core include, but are not limited to, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS, MgSe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP, InGaP, InSb, AlAs, AlN, AlP, AlSb, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, PbTe, Ge, Si, alloys including any of the foregoing, and / or mixtures including any of the foregoing (including ternary and quaternary mixtures or alloys).

[0070] The shell can be a semiconductor material having the same or different composition from that of the core. The shell includes an outer coating of semiconductor material on the surface of the core semiconductor nanocrystal, and the outer coating can include group IV elements, II-VI compounds, II-V compounds, III-VI compounds, III-V compounds, IV-VI compounds, I-III-VI compounds, II-IV-VI compounds, II-IV-VI compounds, II-IV-V compounds, alloys including any of the foregoing, and / or mixtures including any of the foregoing (including ternary and quaternary mixtures or alloys). Examples include, but are not limited to, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS, MgSe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP, InGaP, InSb, AlAs, AlN, AlP, AlSb, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, PbTe, Ge, Si, alloys including any of the foregoing, and / or mixtures including any of the foregoing. For example, a ZnS, ZnSe, or CdS outer coating can be grown on a CdSe or CdTe semiconductor nanocrystal. For example, an outer coating process is described in U.S. Patent 6322901. By adjusting the temperature of the reaction mixture during the outer coating and monitoring the absorption spectrum of the core, a coating material with high emission quantum efficiency and narrow size distribution can be obtained. The outer coating can include one or more layers. The outer coating includes at least one semiconductor material having the same or different composition from that of the core. Preferably, the outer coating has a thickness of about one to about ten monolayers. The outer coating can also have a thickness greater than ten monolayers. In an embodiment, more than one outer coating can be included on the core.

[0071] In an embodiment, the bandgap of the surrounding "shell" material can be greater than the bandgap of the core material. In some other embodiments, the bandgap of the surrounding shell material can be less than the bandgap of the core material. In an embodiment, the shell can be selected to have an atomic spacing close to the atomic spacing of the "core" underlying layer. In some other embodiments, the shell and the core material can have the same crystal structure.

[0072] Examples of semiconductor nanocrystal (core) shell materials include, but are not limited to: red (e.g., (CdSe)ZnS (core) shell), green (e.g., (CdZnSe)CdZnS (core) shell, etc.), and blue (e.g., (CdS)CdZnS (core) shell (also see further the examples of specific wavelength-converting nanoparticles based on semiconductors above)).

[0073] Thus, in an embodiment, the luminescent particle or the luminescent core includes a luminescent material selected from the group consisting of luminescent quantum dots, and the luminescent quantum dots include one or more core materials selected from the group consisting of CdS, CdSe, ZnS, and ZnSe. Thus, in an embodiment, the luminescent particle or the luminescent core can also be selected from a group of luminescent nanoparticles, such as quantum dots or quantum rods with a composition of MX (M = Cd, Zn, X = Se, S). Such particles can have a number-average particle size in the range of 1 - 50 nm (i.e., in particular, length / width / height, diameter).

[0074] As described above, the luminescent particle particularly includes a primary ALD coating disposed on the primer layer. In an embodiment, the luminescent particle can further include another ALD coating disposed at (on) the primary sol-gel coating. The primary ALD coating can be deposited by applying a primary atomic layer deposition process ("primary ALD process"). The another ALD coating can be deposited by applying another atomic layer deposition process ("another ALD process"). The primary atomic layer deposition process and the (optional) additional atomic layer deposition process are both atomic layer deposition processes ("ALD process"). It should be understood that these processes can include the same ALD process. However, for example, the conditions of the primary ALD process may be different from the conditions of the another ALD process. For example, the (multiple) metal oxide precursors used in the primary ALD process can be different from the (multiple) metal oxide precursors used in the another ALD process. The deposition duration may be different, the temperature may be different, and so on. However, in particular, the (multiple) metal oxide precursors that can be applied in the another ALD process can be the (multiple) metal oxide precursors described for the (primary) ALD process (and vice versa).

[0075] Thus, the main ALD coating and an optional further ALD coating can be formed by an atomic layer deposition-type process. In this method, a polymer network is formed by the reaction of a metal oxide precursor with an oxygen source (such as water and / or ozone) in the gas phase. The ALD reaction is divided into (at least) two parts. In the first step, the metal (oxide) precursor is fed into the (ALD) reactor and adsorbs to the reactive groups on the particle surface and / or reacts with the reactive groups on the surface, and substantially all unreacted or unadsorbed precursor molecules are removed by reactor purging. In the second step, the oxygen source is fed into the reactor and reacts with the metal source on the particle surface, and subsequently the reactor is purged to remove substantially all remaining oxygen source molecules and the hydrolysis products formed by the condensation reaction. Due to the self-limiting nature of the surface reaction, these two steps result in the formation of atomic layers (or monolayers). These atomic layer reaction steps are repeated multiple times to form the final ALD coating. The ALD process also allows for the deposition of layers of different compositions by continuously feeding different metal oxide precursors into the reactor to form multi-component layers or nanolaminates with customized chemical, mechanical, and optical properties (see further below).

[0076] The term "metal oxide precursor" particularly denotes a precursor of a metal oxide. The precursor itself may not be a metal oxide, but may include, for example, metal organic molecules. Thus, metal (oxide) precursors for ALD in particular can generally include metal halides, alkoxides, amides, and other metal (organic) compounds. The term metal oxide precursor can refer to more than one different metal oxide precursor, particularly more than one different metal oxide.

[0077] The stepwise nature of the ALD process allows for the easy deposition of a defined layer thickness. The ALD process also allows for the deposition of layers of different compositions by continuously feeding different metal oxide precursors into the reactor to form multi-component layers or nanolaminates. Thus, in a particular embodiment, the main ALD coating (and / or a further ALD coating) comprises multiple layers (or a nanolaminate) (see also below).

[0078] For the ALD process, a fluidized bed reactor can be applied, among other things.

[0079] Thus, in certain embodiments, a primary ALD coating is provided by applying a (primary) atomic layer deposition process. Additionally, in embodiments, another ALD coating is provided by applying another ALD process. In embodiments, a static powder bed is used for ALD coating of the primer layer and / or for ALD coating of the primary sol-gel coating. However, a fluidized bed can also be applied (for one or more ALD processes). Other types of reactors can also be applied. As described above, the primer layer can facilitate the deposition of the primary ALD coating, particularly by acting as a nucleation layer or seed layer for the primary ALD coating. In particular, reactive groups on the particle surface can be provided by the primer layer (and also the primary sol-gel coating).

[0080] For example, silanol groups at the surface of the sol-gel coating (assuming a primary and / or main silica sol-gel coating) act as reaction sites during ALD of the initial layer. In one embodiment, aluminum oxide is deposited by using Al(CH 3 ) 3 (TMA) as the metal oxide precursor and (subsequent exposure to) water as the oxygen source. In the first reaction step, TMA reacts with the surface silanol groups of the silica sol-gel coating according to the following:

[0081] ≡Si-OH + Al(CH 3 ) 3 →≡Si-O-Al(CH 3 ) 2 + CH 4

[0082] Then water reacts with the metal oxide precursor in the second reaction step through a hydrolysis reaction, followed by a condensation reaction:

[0083] ≡Si-O-Al(CH 3 ) 2 + 2H 2 O →≡Si-O-Al(OH) 2 + 2CH 4

[0084] 2≡Si-O-Al(OH) 2 →≡Si-O-Al(OH)-O-Al(OH)-O-Si≡+ H 2 O

[0085] Furthermore, by applying a primer sol-gel layer (and the primary sol-gel coating) having a structured nanoporous surface, such as a silica sol-gel coating (see below), particle agglomeration can be substantially prevented.

[0086] The ALD process can be easily scaled up, and little powder or particle loss is observed during ALD coating. Commercially available ALD reactors for powder coating are sold, for example, by Picosun Oy and come with, for example, cassette sample holders (POCA TM ). Systems that can be used for the ALD process are described, for example, in WO 2013171360 A1, although other systems can also be applied.

[0087] The following table lists (non-limiting) several materials suitable for ALD coatings:

[0088] Oxide material Metal (oxide) precursor Oxygen source Deposition temperature [°C] <![CDATA[Al 2 O 3 > <![CDATA[Al(CH 3 ) 3 (TMA) or HAl(CH 3 ) 2 > <![CDATA[H 2 O or O 3 > 100-400 <![CDATA[HfO 2 > <![CDATA[Hf(N(CH 3 ) 2 ) 4 or Hf(N(CH 2 CH 3 ) 2 ) 4 > <![CDATA[H 2 O]]> 80-300 <![CDATA[Ta 2 O 5 > <![CDATA[TaCl 5 or Ta(N(CH 3 ) 2 ) 5 > <![CDATA[H 2 O]]> 80-300 <![CDATA[ZrO 2 > <![CDATA[ZrCl 4 or Zr(N(CH 3 ) 2 ) 4 > <![CDATA[H 2 O]]> 80-300 <![CDATA[TiO 2 > <![CDATA[TiCl 4 ,Ti(OCH 3 ) 4 or Ti(OEt) 4 > <![CDATA[H 2 O]]> 80-300 <![CDATA[SiO 2 > <![CDATA[SiCl 4 , H 2 N(CH 2 ) 3 Si(OEt) 3 or Si(OEt) 4 > <![CDATA[H 2 O or O 3 > 150-300 .

[0089] Alternatively or additionally, niobium oxide (especially Nb 2 O 5 ) or yttrium oxide (Y 2 O 3 ) can be applied. Its metal precursors are, for example, (tert-butylimino)-tris(diethylamino)-niobium, NbF 5 or NbCl 5 , and tris(ethylcyclopentadienyl)yttrium. In a further embodiment, zinc oxide (ZnO) can be applied. Its metal precursors that can be applied, for example, are diethylzinc (DEZ) Zn(C 2 H 5 ) 2 and dimethylzinc (DMZ) Zn(CH 3 ) 2 . However, other materials can also be applied. Thus, in the atomic layer deposition process, the metal oxide precursors can be particularly selected from the group of metal oxide precursors of metals including Al, Zn, Hf, Ta, Zr, Ti, and Sn (and optionally Si). Alternatively or additionally, metal precursors of one or more metals including Ga, Ge, V, and Nb can be applied. Even more particularly, alternating layers of two or more of these precursors are applied, where at least one precursor is an Al metal oxide precursor and the other precursor is selected from the group consisting of Hf metal oxide precursors, Zn metal oxide precursors, Ta metal oxide precursors, Zr metal oxide precursors, Ti metal oxide precursors, and Sn metal oxide precursors, particularly selected from the group consisting of Hf metal oxide precursors, Ta metal oxide precursors, Ti metal oxide precursors, and Zr metal oxide precursors, for example, selected from the group consisting of Hf metal oxide precursors, Ta metal oxide precursors, and Zr metal oxide precursors, and even more particularly a Ta metal oxide precursor. In particular, Hf, Zr, and Ta seem to provide relatively transparent layers, while Ti, for example, can provide relatively less transparent layers. Using TiCl 4As a metal oxide precursor (for TiO 2 layers) can provide a cost-effective layer. For example, processing with Ta, Hf, and Zr seems to be relatively easier than with Si. The term "oxide precursor" or "metal oxide precursor" or "metal (oxide) precursor" can also refer to a combination of two or more chemically different precursors. These precursors form oxides especially when reacted with an oxygen source (and are thus called metal oxide precursors). In an embodiment, for successive ALD cycles, the metal oxide precursors can be selected independently of each other. For example, in an embodiment, ZnO layers and Al 2 O 3 layers are alternately deposited to obtain an AZO layer (Al 2 O 3 :ZnO, or "aluminum-doped zinc oxide layer"). The AZO layer can be a conductive layer, and can be deposited using, for example, triethylaluminum, diethylzinc, and water as the oxygen source. In a further embodiment, (another) metal oxide is also deposited in a plurality of successive cycles (and optionally another metal oxide is continuously deposited (optionally also in a plurality of successive cycles)).

[0090] Furthermore, the term "metal oxide precursor of a metal comprising Al, Zn, Hf, Ta, Zr, Ti, and Sn" and similar phrases "in an atomic layer deposition process, the metal oxide precursor is selected from metal oxide precursors of a metal comprising Al, Zn, Hf, Ta, Zr, Ti, and Sn" especially refer to metal oxide precursors selected from the group consisting of the given metals (in this regard, Al, Zn, Hf, Ta, Zr, Ti, Sn). Furthermore, in an embodiment, one or more metal oxide precursors are selected. For example, referring to the list given above, a metal oxide precursor "selected from the group of metal oxide precursors of a metal comprising Al, Zn, Hf, Ta, Zr, Ti, and Sn" can include any combination of metal oxide precursors of two or more metals selected from Al, Zn, Hf, Ta, Zr, Ti, and Sn. In an embodiment, for example, the metal oxide precursor includes a combination of TaCl 5 and HAl(CH 3 ) 2 . In a further embodiment, the metal oxide precursor contains only Al(CH 3 ) 3 .

[0091] Thus, in an embodiment, in the main atomic layer deposition process, the metal oxide precursor is selected from the group of metal oxide precursors of metals, and the metals are selected from the group consisting of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V (and optionally Si). In particular, in a further embodiment, in the main atomic layer deposition process, the metal oxide precursor is selected from the group of metal oxide precursors of metals including Al, Hf, Ta, Zr, and Ti (specifically, metal oxide precursors of metals selected from the group consisting of Al, Hf, Ta, Zr, and Ti). In a further embodiment, in the main atomic layer deposition process, metal oxide precursors selected from the group consisting of Al(CH 3 ) 3 , HAl(CH 3 ) 2 , Hf(N(CH 3 ) 2 ) 4 , Hf(N(CH 2 CH 3 ) 2 ) 4 , Hf[N(CH 3 )(CH 2 CH 3 )] 4 , TaCl 5 , Ta(N(CH 3 ) 2 ) 5 , Ta{[N(CH 3 )(CH 2 CH 3 )] 3 N(C(CH 3 ) 3 )}, ZrCl 4 , Zr(N(CH 3 ) 2 ) 4 , TiCl 4 , Ti(OCH 3 ) 4 , and Ti(OCH 2 CH 3 ) 4 are used, and an oxygen source selected from the group consisting of H 2 O and O 3 . Additionally or alternatively, in the (main) atomic layer deposition process, the metal oxide precursor is selected from Zn(C 2 H 5 ) 2 and Zn(CH 3 ) 2A group formed. In another embodiment, additionally or alternatively, in the (main) atomic layer deposition process, the metal precursor is selected from the group consisting of (tert-butylimino)-tris(diethylamino)-niobium, NbF 5 , NbCl 5 and tris(ethylcyclopentadienyl)yttrium.

[0092] In another atomic layer deposition process, the (multiple) metal oxide precursors are particularly independently selected from the (multiple) metal oxide precursors in the main atomic layer deposition process, and can particularly (also) be selected from the group of metal oxide precursors of metals, the metals being selected from the group consisting of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga and V (and optionally Si). In an embodiment, at least one of the (multiple) metal oxide precursors in another atomic layer deposition process is a silicon metal oxide precursor. Particularly, in another embodiment, in another atomic layer deposition process, the metal oxide precursor is selected from the group of metal oxide precursors of metals, the metals being selected from the group consisting of Al, Hf, Ta, Zr and Ti. In an embodiment, in another atomic layer deposition process, the metal oxide precursor (also independently of the main ALD process) is selected from the group consisting of Al(CH 3 ) 3 , HAl(CH 3 ) 2 , Hf(N(CH 3 ) 2 ) 4 , Hf(N(CH 2 CH 3 ) 2 ) 4 , Hf[N(CH 3 )(CH 2 CH 3 )] 4 , TaCl 5 , Ta(N(CH 3 ) 2 ) 5 , Ta{[N(CH 3 )(CH 2 CH 3 )] 3 N(C(CH 3 ) 3 )}, ZrCl 4 , Zr(N(CH 3 ) 2 ) 4 , TiCl 4 , Ti(OCH 3 ) 4 , and Ti(OCH 2 CH3 ) 4 a group consisting of, and an oxygen source selected from the group consisting of H 2 O and O 3 . Additionally or alternatively, in another atomic layer deposition process, the metal oxide precursor is selected from the group consisting of Zn(C 2 H 5 ) 2 and Zn(CH 3 ) 2 . In yet another embodiment, additionally or alternatively, in another atomic layer deposition process, the metal precursor is selected from the group consisting of (tert-butylimino)-tris(diethylamino)-niobium, NbF 5 , NbCl 5 and tris(ethylcyclopentadienyl)yttrium.

[0093] In particular, in an embodiment, in the main atomic layer deposition process and / or another atomic layer deposition process, the metal oxide precursor is selected from the group of metal oxide precursors of metals selected from the group consisting of Al, Zn, Hf, Ta, Zr, Ti, Si, Sn, Nb, Y, Ga, and V.

[0094] The results show that deposition temperatures in the range of 200 - 350 °C are most suitable for alumina ALD on the primer layer (and the main sol-gel coating), with a preferred temperature range of 250 - 300 °C. Similar temperatures can be applied to the ALD of other metal oxide precursors for the (multiple) ALD layers.

[0095] In a particular embodiment, the main ALD coating comprises a multi-layer having at least three layers with different chemical compositions, and one or more of the layers comprise an oxide of Si (SiO 2 ). In particular, such SiO 2 layers are sandwiched between the other layers of the multi-layer. Thus, in particular, the ALD layer (in the multi-layer of the main ALD coating) in contact with the main sol-gel layer and the corresponding (ALD) layer in contact with the primer layer are not composed of SiO 2 . However, in an embodiment, another ALD coating in contact with the main sol-gel coating may comprise SiO 2 . Thus, in an embodiment, in the (main and / or another) atomic layer deposition process, a metal oxide precursor of Si is selected.

[0096] In particular, the main ALD alumina (or other metal oxide) layer has a thickness of 3 - 250 nm, particularly 5 - 250 nm, for example 5 - 100 nm, even more particularly 5 - 50 nm, for example particularly 10 - 50 nm, and even more particularly 20 - 50 nm.

[0097] By depositing an additional layer of at least one different oxide material (such as ZrO 2 , TiO 2 , Y 2 O 3 , Nb 2 O 5 , HfO 2 , Ta 2 O 5 ), the water vapor permeation barrier performance of the alumina ALD layer can be further improved. In particular, the thickness of the additional material layer is in the range of 1 - 40 nm, more preferably in the range of 1 - 10 nm. Even more particularly, it is an alternating nanolaminate stack of Al 2 O 3 and a second oxide material from the group consisting of ZrO 2 , TiO 2 , Y 2 O 3 , Nb 2 O 5 , HfO 2 , SiO 2 , Ta 2 O 5 group. A suitable nanolaminate stack can be, for example, 20x(1 nm Al 2 O 3 (10 ALD cycles) + 1 nm ZrO 2 (11 ALD cycles)) deposited at 250 °C to form a 40 nm thick nanolaminated second coating on the primer layer (and / or the main sol - gel coating).

[0098] The present invention particularly provides a method in an embodiment, wherein the main ALD coating comprises multiple layers with layers having different chemical compositions, and wherein in the atomic layer deposition process, the metal oxide precursors are particularly selected from the group of metal oxide precursors of metals selected from the group consisting of Al, Zn, Hf, Ta, Zr, Ti, Sn, Y, Ga, Ge, V, and Nb (and optionally Si), in particular the metal oxide precursors are selected from the group of metal oxide precursors of metals selected from the group consisting of Al, Hf, Ta, Zr, and Ti. Combinations of two or more such precursors can also be used, such as a multilayer comprising a mixed oxide - alumina of alumina - zirconium and hafnium, and so on. In a specific embodiment, in the main atomic layer deposition process, the metal oxide precursors for two or more layers are selected from the group of metal oxide precursors of metals selected from the group consisting of Al, Hf, Ta, Zr, and Ti.

[0099] Thus, in an embodiment, the main ALD coating may comprise a multi-layer having (n number of) layers with different chemical compositions, and wherein the multi-layer comprises one or more layers comprising one or more oxides of Al, Zn, Hf, Ta, Zr, Ti, Sn, Y, Ga, Ge, V, and Nb (and optionally Si), especially wherein the multi-layer comprises one or more layers comprising one or more oxides of Al, Hf, Ta, Zr, and Ti. One or more layers in such a multi-layer may also comprise mixed oxides, as indicated above.

[0100] In a further specific embodiment, the method of the present invention comprises successively providing n layers (onto a primer layer by applying a main atomic layer deposition process), especially wherein each layer has a coating thickness (d21) of 1 - 50 nm, especially 1 - 20 nm, for example 1 - 15 nm. In an embodiment, the layer coating thickness may be at least 2 nm, for example at least 5 nm, and for example in the range of 5 - 40 nm, especially 5 - 25 nm. The number of layers n is especially at least 2, for example at least 3, or at least 4. In an embodiment, n may be greater than 10. However, n is especially equal to or less than 10, for example equal to or less than 5. In an embodiment, 2 ≤ n ≤ 10, or especially 2 ≤ n ≤ 5. It should be understood that a single layer may be provided by one or more ALD cycles. Furthermore, especially adjacent (contacting) layers contain different chemical compositions. In a further embodiment, one or more layers comprise one or more metal oxides selected from the group consisting of HfO 2 、ZrO 2 、TiO 2 、Ta 2 O 5 , especially wherein one or more (other) layers comprise Al 2 O 3 . It appears more advantageous when the layer in contact with the main sol - gel coating consists of HfO 2 and / or ZrO 2 and / or TiO 2 and / or Ta 2 O 5 . Thus, in a further embodiment, the layer in contact with the main sol - gel coating consists of one or more metal oxides selected from the group consisting of HfO 2 、ZrO 2 、TiO 2 、Ta 2 O 5 .

[0101] Thus, in a specific embodiment, the method includes continuously providing n (ALD) layers (to provide a multi-layer) on the primer layer by applying a main atomic layer deposition process, where each layer has a coating thickness (d21) of 1 - 50 nm, particularly 1 - 20 nm, for example 1 - 15 nm, and where 2 < n ≤ 50, particularly 2 < n ≤ 20, for example 2 ≤ n ≤ 10, particularly 2 ≤ n ≤ 5, and where one or more layers comprise a group selected from HfO 2 、ZrO 2 、TiO 2 、Ta 2 O 5 and where one or more layers comprise Al 2 O 3 , and where the layer in contact with the main sol-gel coating is composed of one or more metal oxides selected from the group consisting of HfO 2 、ZrO 2 、TiO 2 、Ta 2 O 5 .

[0102] In particular, applying the method results in obtaining an (n ALD) multi-layer coating (especially the main ALD coating) including at least two (ALD) layers ("AB"), even more particularly at least three layers (e.g., "ABA"), even more particularly at least four layers. More particularly, at least applying a stack including a stack of subsets each including two or more two (ALD) layers ("AB"), e.g., (AB) n , where n is 2 or greater, e.g., 2 - 20, such as 2 - 10.

[0103] In particular, at least one layer of the multi-layer comprises an oxide of Al (optionally in combination with another oxide such as Si or another metal oxide described herein), and at least one layer of the multi-layer comprises one or more of the oxides of Hf, Zn, Ta, Zr, Ti, Y, Ga, Ge, V, Sn, and Nb. Such a layer may also optionally include Al, Zn, Hf, Ta, Zr, Ti, Sn, (Si), Y, Ga, Ge, V, and Nb, where Al is in one layer with one or more of the other specified elements when the other layer(s) of the multi-layer comprise(s) an oxide of aluminum. The term "ALD multi-layer" or "multi-layer" as described above particularly refers to layers having different chemical compositions. The phrase "layers having different chemical compositions" means that at least two layers have different chemical compositions, for example, in the case of "ABC", or in the case of (AB) n (where n ≥ 1).

[0104] (AB) nSpecific examples include multilayers where A is an oxide of Al and where B is selected from one or more of the oxides of Al, Zn, Hf, Ta, Zr, Ti, Sn, Y, Ga, Ge, V, and Nb, where when the (multiple) other layers of the multilayer each contain an oxide of aluminum, Al (and / or optionally Si) is in one layer together with one or more of the other specified elements, especially where B is selected from one or more of the oxides of Hf, Zn, Ta, Zr, Ti, Y, Ga, Ge, V, and Nb, and even more especially where B is selected from one or more of the oxides of Hf, Ta, Zr, and Ti, more especially where B is selected from one or more of the oxides of Hf, Ta, and Zr. In an embodiment, B can further include an oxide of Si (optionally in combination with one or more of the oxides of Al, Zn, Hf, Ta, Zr, Ti, Sn, Y, Ga, Ge, V, and Nb). In particular, if SiO 2 layers are deposited, then SiO 2 (ALD) layers are deposited such that it does not directly contact the main sol-gel layer. For example, the A layer (or B layer) of the multilayer can be a SiO 2 layer, and the B layer (or A layer) that contacts the main sol-gel layer can be an (ALD) layer having another chemical composition.

[0105] This main ALD multilayer is thus especially provided on the primer layer. The main sol-gel layer is especially provided on the main ALD multilayer. In addition, as described above, on top of the main sol-gel layer, one or more additional layers can optionally be applied, especially another ALD layer can be provided on top of the main sol-gel layer. This other ALD layer can include an ALD multilayer, such as the ALD multilayer described herein in relation to the main ALD multilayer.

[0106] In a further specific embodiment, the method further includes (iv) providing another ALD coating on the luminescent core having the main sol-gel coating by applying a further atomic layer deposition process. In particular, another ALD-coated luminescent particle is thereby provided. In the further atomic layer deposition process, especially the metal oxide precursor is selected from the group of metal oxide precursors including Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V (and optionally Si) - especially including Al, Hf, Ta, Zr, Ti. In an embodiment, the other ALD coating has another ALD coating thickness (d4) in the range of 2 - 50 nm, especially 10 - 50 nm, for example 10 - 20 nm. The other ALD coating especially has a chemical composition different from that of the main sol-gel coating.

[0107] In another embodiment, another ALD coating (optionally) comprises (is provided as comprising) another multilayer having two or more (additional sub)layers with different chemical compositions, where one or more of the layers comprise a metal oxide selected from the group consisting of Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , SnO 2 , ZnO and Ta 2 O 5 , and where two or more of the layers have a chemical composition different from that of the main sol-gel coating. In a particular embodiment, in another atomic layer deposition process, the metal oxide precursors for two or more (additional sub)layers of the (another multilayer) are selected from the group of metal oxide precursors of metals selected from the group consisting of Al, Hf, Ta, Zr, and Ti. The metal oxide precursors for two or more (additional sub)layers of the (another multilayer) are particularly selected from the group of metal oxide precursors comprising Al, Hf, Ta, Zr, Ti.

[0108] Thus, in a specific embodiment, the main ALD coating comprises a multilayer having stacked layers, where adjacent layers have different chemical compositions. In particular, each layer of the multilayer independently has a thickness of 1 - 40 nm, particularly 1 - 10 nm. Further, in particular, the multilayer comprises one or more alumina layers and one or more metal oxide layers, where the metal is selected from the group consisting of Hf, Ta, Zr, and Ti.

[0109] Thus, in a specific embodiment of the atomic layer deposition process, there is applied a compound selected from the group consisting of Al(CH 3 ) 3 , HAl(CH 3 ) 2 , Hf(N(CH 3 ) 2 ) 4 , Hf(N(CH 2 CH 3 ) 2 ) 4 , Hf[N(CH 3 )(CH 2 CH 3 )] 4 , TaCl 5 , Ta(N(CH 3 ) 2 ) 5 , Ta{[N(CH 3 )(CH 2 CH 3 )] 3 N(C(CH3 ) 3 )}, ZrCl 4 , Zr(N(CH 3 )) 2 ) 4 , TiCl 4 , Ti(OCH 3 )) 4 , and Ti(OCH 2 CH 3 )) 4 comprising a metal oxide precursor of the group consisting of, and an oxygen source selected from the group consisting of H 2 O and O 3 . As described above, two or more different metal oxide precursors and / or two or more different oxygen sources can also be applied.

[0110] Furthermore, in embodiments of the method in the main atomic layer deposition process and / or another atomic layer deposition process, particularly in the main atomic layer deposition process, multiple layers are provided, which have different chemical compositions, and one or more of the layers comprise tantalum oxide (particularly Ta 2 O 5 ). Thus, in an embodiment, the present invention also provides a luminescent material, wherein the main ALD coating comprises multiple layers of layers having different chemical compositions, and one or more of the layers can particularly comprise Ta 2 O 5 . Furthermore, in embodiments of the method in the (main) atomic layer deposition process, multiple layers are provided, wherein each layer has a different chemical composition, and one or more of the layers comprise one or more of tantalum oxide (especially Ta 2 O 5 ), hafnium oxide, titanium oxide, and zirconium oxide. Thus, in an embodiment, the present invention also provides a luminescent material, particularly luminescent particles, wherein the main ALD coating comprises multiple layers having different chemical compositions, and one or more of the layers can particularly include one or more of tantalum oxide, hafnium oxide, titanium oxide, and zirconium oxide. For example, the multiple layer stack can also include a stack having alternating layers, wherein for example, alumina alternates with one or more of tantalum oxide (especially Ta 2 O 5 ), hafnium oxide, titanium oxide, and zirconium oxide, such as a stack including, for example, alumina - tantalum oxide - alumina - hafnium oxide - alumina - tantalum oxide, or alumina - titanium oxide - alumina, etc.

[0111] In addition, when an ALD coating is provided on the core for the first time without a primer layer, the ALD layer does not appear to be as uniform as desired. In order to obtain a good ALD layer directly on the core surface, in such embodiments, the thickness of the ALD layer may have to be increased to more than would be necessary in principle, which may lead to an unnecessary reduction in transmittance (even if small in some cases). In addition, it appears that after providing a primer layer at the core (even if not fully conformal), the ALD coating is more easily applied to the core.

[0112] As described above, the main sol-gel layer generally has an average thickness in the range of 50 - 700 nm, such as 50 - 600 nm, especially 75 - 500 nm, such as especially 100 - 500 nm, and is formed by a sol-gel type process. In such a process, the inorganic network is formed from a homogeneous solution of precursors, through subsequent hydrolysis to form a sol (colloidal suspension) and condensation to form a gel (cross-linked solid network), which is chemically bonded to the powder surface. Preferably, the (main) sol-gel coating material is silica, and the sol-gel deposition method corresponds to the so-called reaction (as described by W, A. Fink, et al. “Controlled growth of micron-sized monodisperse silica spheres”, Journal of Colloid and Interface Science 26(1): 62 - 69). For this purpose, the (coated or uncoated) luminescent particles are dispersed in an alcohol, such as a fatty alcohol R-OH (e.g., methanol CH 3 OH, ethanol C 2 H 5 OH or isopropanol C 3 H 7 OH), and subsequently ammonia (aqueous NH3 solution) and a silanolate precursor are added. The silanolate precursor is dissolved in the alcohol + ammonia mixture and starts to hydrolyze. A conformal silica coating is formed on the surface of the (coated or uncoated) particles through the reaction of the hydrolyzed but dissolved sol material with the reactive groups on the particle surface (such as amine or silanol groups), followed by a seeding growth process consisting of hydrolysis, nucleation, and condensation reaction steps.

[0113] The term “(coated or uncoated) particle surface” related to the sol-gel coating process may particularly relate to the surface of the particles (luminescent cores) and / or the surface of the washing result layer (especially the oxide-containing layer) on the particles (luminescent cores), which is especially related to the primary sol-gel coating process. This term may further relate to the surface of the main ALD coating, especially in relation to the main sol-gel coating process.

[0114] The silanolate precursor is particularly selected from a group of compounds formed by the following:

[0115]

[0116] wherein a) R1, R2, R3 are hydrolyzable alkoxy groups, and R4 is selected from the group consisting of C1-C6 straight-chain alkyl groups, hydrolyzable alkoxy groups, and phenyl groups, or b) R1, R2, R3 are each independently selected from -OCH 3 and -OC 2 H 5 , and R4 is selected from -CH 3 , -C 2 H 5 , -OCH 3 , -OC 2 H 5 and phenyl. Optionally, the silicone-based polymer is obtained from materials from the group consisting of:

[0117]

[0118] Thus, in an embodiment of the method, in the main sol-gel coating process, a silanolate precursor is used, wherein the silanolate precursor is particularly selected from the group of compounds consisting of:

[0119]

[0120] wherein a) R1, R2, R3 are hydrolyzable alkoxy groups, and R4 is selected from the group consisting of C1-C6 straight-chain alkyl groups, hydrolyzable alkoxy groups, and phenyl groups, or b) R1, R2, R3 are each independently selected from -OCH 3 and -OC 2 H 5 , and R4 is selected from -CH 3 , -C 2 H 5 , -OCH 3 , -OC 2 H 5 and phenyl.

[0121] In a further embodiment of the method, in the main sol-gel coating process, a silanolate precursor is used, and the silanolate precursor is selected from the group consisting of:

[0122]

[0123] In a further embodiment of the method, in the primary sol-gel coating process, a silanolate precursor is used, and in particular, the silanolate precursor can be the silanolate precursor as described herein for the main sol-gel coating process. The silanolate precursor in the primary sol-gel coating process can be independently selected from the silanolate precursor in the main sol-gel coating process.

[0124] In particular, the silanolate precursor (in the main and / or primary sol-gel coating process) is selected from Si(OCH 3) 4 or Si(OC 2 H 5 ) 4 groups, and more particularly, Si(OC 2 H 5 ) 4 is used as a silanolate precursor. Similar precursors can also be used, but based on another metal, such as, for example, Al.

[0125] Typical sol-gel coating processes can include the following stages: (a) While stirring or sonicating, suspend particles or powders, especially luminescent nuclei (optionally having an oxide-containing layer and / or a primary ALD coating), in an alcohol-ammonia aqueous solution mixture. To improve particle dispersion, the particles (nuclei / powders) can also first be mixed with alcohol and a small amount of silicon (or other metal) alkoxide before adding the ammonia solution. (b) Add a silicon (or other metal) alkoxide precursor under stirring of the suspension. Typical concentrations of alkoxysilicon (or other metal) salts, ammonia, and water in the alcohol solvent are 0.02 - 0.7, 0.3 - 1.5, and 1 - 16 moles per liter, respectively. (c) Stir or sonicate the suspension until a coating is formed. (d) Wash the coated powder with alcohol and dry it, and then calcine it in air or in vacuo at 200 - 300 °C.

[0126] Thus, in an embodiment, the primary sol-gel coating process includes: (iiia) providing a mixture of alcohol, ammonia, water, (multiple) luminescent nuclei having a (primer layer and) primary ALD coating, and a metal alkoxide precursor, while stirring the mixture and allowing a primary sol-gel coating to form on the primary ALD coating, wherein the metal alkoxide precursor is particularly alkoxytitanium, alkoxysilicon, or alkoxyaluminum; and (iiib) retrieving the (multiple) luminescent nuclei having a (primer layer,) primary ALD coating, and a primary sol-gel coating from the mixture, and optionally subjecting the retrieved (multiple) luminescent nuclei having a primer layer, primary ALD coating, and primary sol-gel coating to a heat treatment to provide the (multiple) luminescent particles having a hybrid coating.

[0127] Thus, in a further embodiment, the primary sol-gel coating process comprises: (ib1) providing a mixture of an alcohol, ammonia, water, one or more luminescent cores (optionally having a wash result layer), in particular one or more luminescent cores and a wash result layer (or one or more luminescent cores comprising a wash result layer) and a metal alkoxide precursor, while stirring the mixture and allowing a primary sol-gel coating to form on the wash result layer and / or on the one or more luminescent cores without a wash result layer, in particular on the wash result layer, wherein the metal alkoxide precursor is particularly selected from titanium alkoxides, silicon alkoxides or aluminium alkoxides; and (ib2) retrieving the one or more luminescent cores having the (wash result layer and) primary sol-gel coating from the mixture and optionally subjecting the retrieved one or more luminescent cores having the (wash result layer and) primary sol-gel coating to a heat treatment to provide one or more luminescent cores comprising a primer layer on the luminescent cores.

[0128] The process of retrieving the one or more cores (with their respective (coating) layers) from the mixture can for example comprise one or more of filtration, centrifugation, decantation (the liquid on the precipitate), etc. The heat treatment can comprise one or more of drying and calcination, in particular both, i.e. for example a drying stage at a temperature in the range of 70 - 130 °C, followed by a calcination stage (in air; or in vacuum or (other) inert atmosphere). Thus, during part of the heat treatment, the (coated) luminescent material can be in an inert environment, such as vacuum, or N 2 and one or more of inert gases, etc. The heat treatment seems to improve the stability of the luminescent material. Furthermore, as mentioned above, in the (main and / or primary) sol-gel coating process, the silicon (or other metal; although the chemical formula below refers to Si) alkoxide (in particular the precursor) can be used from a group of compounds consisting of:

[0129]

[0130] wherein R1, R2, R3 are selected from the group consisting of hydrolyzable alkoxy moieties, and R4 is selected from the group consisting of C1 - C6 straight-chain alkyl moieties, hydrolyzable alkoxy moieties and phenyl moieties. Optionally, other ligands different from alkoxides can be applied to the precursors of the sol-gel process.

[0131] The particles obtained with the sol-gel coating process can optionally comprise more than one core. For example, in the case of quantum dots, aggregates having a (primary and / or main) sol-gel coating can be obtained. Thus, a silica precursor (or other metal oxide precursor) can also coat a plurality of QDs (in particular comprising a main ALD coating) with a thin single shell to form coated aggregates. This depends in particular on the concentration of the quantum dots, etc.

[0132] Above, the precursor of the sol-gel coating was specifically described as a silanolate precursor. However, an aluminum (or another metal) alkoxide precursor can also be applied. In addition, a combination of two or more chemically different precursors can also be applied to provide a sol-gel coating or a first coating.

[0133] The term "sol-gel coating process" can also refer to multiple sol-gel coating processes. By using multiple sol-gel coating processes, especially multiple main sol-gel coating processes, a (multi)layer that basically includes the same composition throughout the layer thickness can be provided (for example, when in the (main) sol-gel coating process, each coating stage or step includes depositing basically the same material), or a multi-layer with two or more layers having different compositions can be provided, such as a stack of two or more (sol-gel) layers each having two or more different compositions. An example can be, for example, SiO 2 -Al 2 O 3 (sol-gel) multi-layer, such as a stack of three or more (sol-gel) layers, where SiO 2 and Al 2 O 3 alternate (see also above).

[0134] To facilitate the deposition of the main ALD coating, the luminescent core can include a primer layer. In an embodiment, the primer layer includes a primary sol-gel coating (optionally including a multi-layer), especially provided by a (primary) sol-gel coating process. The primary sol-gel coating can facilitate the deposition of a (thin) conformal main ALD coating. To further support the deposition of the main ALD coating, in an embodiment, the surface of the core is cleaned before providing the primary sol-gel layer and / or the main ALD coating.

[0135] To facilitate the main ALD deposition process and, in particular, to enable the deposition of a single ALD layer or multiple layers with as few defects as possible, any chemical reaction contaminants (also referred to as "second phase") that may be present in the powder (coarse product, especially including multiple luminescent nuclei) can be removed. Preferably, small particles, typically having submicron dimensions, and small particles that may adhere to the surface of the phosphor particles (luminescent nuclei) are also removed prior to the deposition of the main ALD coating process. Cleaning of the nuclei surface can particularly include a (chemical) washing process. In an embodiment, the nuclei can be washed by applying a washing process and by applying an aqueous liquid. Such an aqueous liquid can contain an acid or a base or can consist, for example, of water (having a neutral pH). Water can be used, for example, to remove small unwanted particles and parts of the second phase. However, to remove additional impurities, the pH value of the aqueous liquid can be changed, for example, to a pH value of at least 8, especially at least 9, or to a pH value below 6, especially below 5. In this way, for example, impurities can be dissolved. In a further embodiment, a non-aqueous solvent can be applied, especially for particles (nuclei) that may be sensitive to water. Thus, in particular, an aqueous liquid containing additives (e.g., to change the pH value), a non-aqueous solvent, or a combination of these liquids / solvents can be applied. Thus, the cleaning / washing process can be referred to as a "chemical washing process", especially by applying a washing solvent (including an aqueous liquid).

[0136] If the chemical stability of the phosphor (luminescent nucleus) in water, base, and / or acid is limited, a washing procedure under very mild conditions can be applied to remove the second phase without dissolving (partially) the phosphor particles. This can be achieved by selecting a weak acid with a pK a value instead of a strong acid, which value can be selected based on the stability of the phosphorus and impurity phases (see below). Additionally or alternatively, by first applying a non-aqueous solvent to the (multiple) luminescent nuclei (phosphors) to provide a suspension of (the luminescent particles / nuclei) and then successively adding a weak acid (or base) such that the total amount of water and the concentration of the acid are sufficient to dissolve only the impurity phase, degradation of the phosphor during the washing process can be avoided.

[0137] A washing solvent with a pH less than 7 can be used for hydrolysis-sensitive luminescent materials because such luminescent materials disclosed herein react as bases in an aqueous medium. The acidity of such a washing solvent may be low. Specifically, an organic acid - such as acetic acid diluted in a polar solvent with a low proton concentration (such as a fatty alcohol (such as ethanol or isopropanol)), as described above - can be used as a washing solvent. The more sensitive the luminescent material, the more diluted the washing solvent should be (i.e., the lower the proton concentration), because the goal of the washing process is to remove the basic impurity phase and create a surface on the particulate luminescent material that aids in the adhesion of the subsequent primer layer without degrading the luminescent material. Generally, if a person of ordinary skill in the art observes that too many particulate luminescent materials degrade or dissolve during the washing process, reducing the acid concentration, replacing the solvent with another solvent having a lower dielectric constant, and / or cooling the washing suspension can reduce the amount of degradation.

[0138] After washing, the number of fine particles in the phosphor powder can be further reduced by precipitation in a non-reactive liquid (usually a polar organic solvent such as, for example, absolute ethanol or other alcohols). In an embodiment, ultrasonic waves are applied to the suspension before sedimentation to better separate and disperse the fine particles from the larger phosphor particles.

[0139] As a result of the chemical washing process, a thin layer with a different composition can form on the surface of the particles (nuclei) compared to the nominal composition of the luminescent particles (luminescent nuclei). That is, the surface composition of the particulate luminescent particles may be somewhat different from the overall composition of the particulate luminescent material. In particular, the thin layer (i.e., the surface) can contain a higher oxygen concentration (content) than the luminescent nucleus (nominal composition). In an embodiment, applying chemical washing can provide a washing result layer on the luminescent nucleus. The washing process can provide a surface (washing result layer) that aids in the adhesion of the subsequent primer layer. When, for example, a hydrolysis-sensitive luminescent material of the alkaline earth aluminate type (such as those disclosed herein) is to be coated, the thin layer / surface can contain, for example, alkaline earth elements (such as strontium), aluminum, and oxides. Depending on the luminescent material, the surface layer can contain elements such as lithium, silicon, europium, carbon, and / or hydrogen. The washing result layer particularly includes an oxide-containing layer. The washing result layer does not necessarily conformally and / or completely cover the surface of the luminescent nucleus (see also the above regarding the primer layer). The washing result layer can be a non-continuous layer and can, for example, include multiple layer portions, each layer portion covering only a part of the surface of the luminescent nucleus. In an embodiment, the washing result layer can be evenly distributed on the surface of the luminescent nucleus. In an embodiment, the washing result layer can cover at least 30%, for example at least 50%, particularly at least 75%, for example at least 90%, or particularly at least 95%, or even more particularly at least 99% of the nucleus surface.

[0140] Experimentally, it has been noted that even when using mild washing solvents, a washed result layer can be observed. In particular, in the case of nitride or oxynitride compounds, the O:N ratio in the washed result layer may be higher. The luminescent core particularly comprises a nitride or oxynitride compound. In embodiments, the luminescent material (especially the luminescent material of the luminescent core) comprises a nitride luminescent material (core). In further embodiments, the luminescent material (especially the luminescent material of the luminescent core) (also) comprises an oxynitride luminescent material (core).

[0141] Thus, in further embodiments, the method further comprises (ia) providing a washed result layer on the luminescent core by applying a chemical washing process, especially wherein the washed result layer comprises an oxide-containing layer. In further embodiments, the application of the chemical washing process comprises drying the luminescent core after removing the washing solvent. The washed result layer can be provided during the washing of the luminescent core with the washing solvent and / or during the drying of the luminescent core. In further embodiments, a primary sol-gel coating is provided after applying the chemical washing process (optionally including the drying of the luminescent core). The application of the chemical washing process can provide washed luminescent particles on the luminescent core comprising the washed result layer.

[0142] Thus, in further embodiments, the method further comprises providing a primary sol-gel coating layer on the luminescent core and the washed result layer (or on the luminescent core comprising the washed result layer) by applying a primary sol-gel coating process, thereby providing a primer layer comprising the washed result layer and the primary sol-gel layer, and especially wherein the primer layer has a primer layer thickness (d1) in the range of 0.1 - 5 nm.

[0143] In embodiments, the washing solvent can comprise an aqueous solvent. Here, this (washing with a solvent comprising an aqueous solvent) can also be referred to as a "wet chemical washing process". In embodiments, for example, the washing solvent comprises a strong acid or a strong base. These terms are known in the art. Examples of strong acids are HCl, HBr, HClO 4 、HI、HNO 3 . Examples of strong bases are, for example, NaOH, KOH, CaOH. However, in further embodiments, the washing solvent comprises a weak acid or a weak base. Examples of weak acids that can be used are, for example, acetic acid, formic acid, hydrofluoric acid, trichloroacetic acid, citric acid, oxalic acid, etc. Examples of weak bases are, for example, ammonia, sodium bicarbonate, alanine, and methylamine.

[0144] The weak acid or weak base can be particularly selected to have a pK a value or pK bValue. In an embodiment, the washing solvent comprises one or more weak acids selected from the group consisting of acetic acid, formic acid, hydrofluoric acid, trichloroacetic acid, citric acid, and oxalic acid. The washing solvent may particularly comprise formic acid or acetic acid. In a further embodiment, the washing solvent comprises one or more weak bases ammonia, sodium bicarbonate, alanine, and methylamine. The washing solvent may particularly comprise a combination of a non-aqueous fluid and a weak acid or a weak base. For example, in an embodiment, the washing solvent may comprise an alcohol (such as propanol, isopropanol, ethanol, (cyclo)hexanol, or any other alcohol having one or more hydroxyl groups) and a weak acid (such as formic acid and / or acetic acid). Alternatively, in an embodiment, the washing solvent may comprise a mixture of an alcohol and a polyol. In an embodiment, for example, the washing solvent comprises a mixture of ethanol and triethylene glycol, particularly a trace amount of water as a dissolution catalyst. Such a combination can be advantageously applied to wash luminescent particles (cores) that may be prone to degradation under the influence of water. In an embodiment, the washing solvent may comprise less than 50 wt% water (relative to the weight of the washing solvent). The washing solvent may, for example, comprise equal to or less than 40 wt% water, such as equal to or less than 35 wt% water. In an embodiment, the washing solvent may comprise no more than 25 wt% water. In particular, the washing solvent (which comprises a (weak) base or a (weak) acid) comprises at least 5 wt% water, such as at least 10 wt% water. However, in an embodiment, the washing solvent is a non-aqueous washing solvent. Furthermore, the application of weak acids (and weak bases) may have additional benefits as they can provide a pH buffering function. Thus, if an additional amount of a weak acid (or weak base) is added to the washing solvent (e.g., if the washing solvent has not removed all impurities), the pH of the washing solvent may not change significantly. The use of weak acids or weak bases can increase the stability of the wet washing process.

[0145] Thus, in a further embodiment, the chemical washing process may particularly comprise a wet chemical washing process, which comprises (i) washing the luminescent core (process) by applying a washing solvent, wherein the washing solvent comprises a (weak) acid or a (weak) base, particularly a (weak) acid, and wherein the washing solvent comprises equal to or less than 50% wt / wt water, particularly water in the range of 10 - 35% wt / wt, and optionally (ii) continuously drying the luminescent core, thereby providing the luminescent core with a washing result layer thereon.

[0146] In particular, based on the washing process (optionally including a drying treatment), an oxygen-containing layer can be provided on the luminescent particles.

[0147] The different (coated) layers (main layer, main ALD layer, main sol-gel coating, and another ALD coating) that can be disposed at the luminescent core are particularly light-transmissive. This means that at least a portion of the light incident on the corresponding layer passes through the corresponding layer. Thus, the different (coated) layers can be fully or partially transparent, or can be translucent. In one embodiment, more than 90% of the (visible) light incident on the (coated) layer passes through the (coated) layer. Due to the properties of the materials used to fabricate the coating, the (coated) layer can be light-transmissive. For example, the coating can be made of a transparent material, even if the layer is relatively thick. In another embodiment, one or more of the (coated) layers are thin enough such that the corresponding layer becomes light-transmissive, while the material used to fabricate the layer is opaque or translucent when fabricated as a relatively thick layer. All of the materials described herein can transmit (visible) light, or can be made into a suitable layer thickness that transmits (visible) light.

[0148] In another aspect, the present invention also provides an illumination device that includes a light source and a wavelength converter. The light source is configured to generate light source radiation, particularly one or more of blue and UV. The wavelength converter includes a luminescent material as described herein, wherein the wavelength converter is configured to convert at least a portion of the light source radiation into wavelength converter light (e.g., one or more of green, yellow, orange, and red light). The wavelength converter is particularly radiation-coupled to the light source. The term "radiation-coupled" particularly means that the light source and the luminescent material are associated with each other such that at least a portion of the radiation emitted by the light source is received by the luminescent material (and at least partially converted into luminescence). Thus, the luminescent core of the particles can be excited by the light source radiation, thereby providing luminescence of the luminescent material in the core. In an embodiment, the wavelength converter includes a matrix (material) that contains the luminescent material (particles). For example, the matrix (material) can include one or more materials selected from the group consisting of transmissive organic material carriers, such as selected from the group consisting of: PE (polyethylene), PP (polypropylene), PEN (polyethylene naphthalate), PC (polycarbonate), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) (Plexiglas or Perspex), cellulose acetate butyrate (CAB), silicone resin, polyvinyl chloride (PVC), polyethylene terephthalate (PET), PETG (ethylene glycol-modified polyethylene terephthalate), PDMS (polydimethylsiloxane), and COC (cycloolefin copolymer). Alternatively or additionally, the matrix (material) can include an epoxy resin.

[0149] When forming such an illumination device, using the coatings disclosed herein allows hydrolysis-sensitive phosphors to be used as the luminescent material in the wavelength converter. In particular, luminescent materials that may degrade under the conditions used to form the matrix can be used in the illumination device (as follows Figure 3As shown), luminescent particles are embedded in the matrix to form a wavelength converter. For example, alkaline earth aluminate luminescent materials, or luminescent materials having a surface layer of alkaline earth aluminate type after the washing process disclosed herein. Such hydrolysis-sensitive luminescent materials include, for example, the luminescent particles disclosed above, which include those selected from (the) SrLiAl 3 N 4 :Eu 2+ (category) of luminescent materials, wherein, optionally, part of Sr can be replaced by another alkaline earth metal (Group 2 element of the periodic table). And also, for example, those selected from the group consisting of (Sr,Ca)LiAl 3 N 4 :Eu, (Sr,Ca,Ba)Li d Mg a Al b N 4 :Eu, where 0 ≤ a ≤ 4, 0 ≤ b ≤ 4, 0 ≤ d ≤ 4; and a + b + d = 4 and 2a + 3b + d = 10, and those selected from (Sr,Ba)Li 2 Al 2-z Si z O 2-z N 2+z :Eu, where 0 ≤ z ≤ 0.1, as described above. And also, for example, SrLi 2 Al 2- x SiO 2-x N 2+x :Eu or (Sr,Ca)SiAlN 3 :Eu disclosed herein. The use of the coatings disclosed herein allows such hydrolysis-sensitive luminescent materials to be used in the process of forming a wavelength converter, for example, in the process of forming a wavelength converter in which luminescent particles are embedded in a matrix such as silicone resin, otherwise the matrix may degrade the uncoated luminescent material.

[0150] The lighting device can be a part of the following, or can be applied to the following: for example, office lighting systems, home application systems, store lighting systems, home lighting systems, accent lighting systems, spotlight lighting systems, theater lighting systems, fiber optic application systems, projection systems, self-luminous display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, decorative lighting systems, portable systems, motor vehicle applications, greenhouse lighting systems, horticultural lighting, or LCD backlighting.

[0151] As described above, the lighting unit can be used as a backlight lighting unit in an LCD display device. Accordingly, the present invention also provides an LCD display device including the lighting unit (configured as a backlight lighting unit) defined herein. In a further aspect, the present invention also provides a liquid crystal display device including a backlight lighting unit, wherein the backlight lighting unit includes one or more lighting devices as defined herein.

[0152] In particular, the light source is a light source that emits (light source radiation) light having at least a wavelength in the range of 200 - 490 nm during operation, in particular a light source that emits light having at least a wavelength in the range of 400 - 490 nm, and even more particularly in the range of 440 - 490 nm during operation. This light can be partially used by the wavelength converter nanoparticles (see also further below). Thus, in a particular embodiment, the light source is configured to produce blue light. In a particular embodiment, the light source includes a solid-state LED light source (such as an LED or a laser diode). The term "light source" can also relate to a plurality of light sources, such as 2 - 20 (solid-state) LED light sources. Thus, the term LED can also refer to a plurality of LEDs. The term white light herein is known to those skilled in the art. It particularly relates to light having a correlated color temperature (CCT) between approximately 2000 and 20000 K, especially between 2700 - 20000 K, for general lighting (especially in the range of approximately 2700 K and 6500 K), and for backlight lighting purposes (especially in the range of approximately 7000 K and 20000 K), and especially within approximately 15 SDCM (standard deviation of color matching) from the BBL (black body locus), especially within approximately 10 SDCM from the BBL, and even more particularly within approximately 5 SDCM from the BBL. In one embodiment, the light source can also provide light source radiation having a correlated color temperature (CCT) between approximately 5000 and 20000 K, such as a directly phosphor-converted LED (a blue light-emitting diode with a thin phosphor layer, for example, to obtain 10000 K). Thus, in a particular embodiment, the light source is configured to provide light source radiation having a correlated color temperature in the range of 5000 - 20000 K, and even more particularly in the range from 6000 - 20000 K (such as 8000 - 20000 K). The advantage of a relatively high color temperature can be that there can be a relatively high blue component in the light source radiation.

[0153] The term "control" and similar terms refer in particular at least to determining the behavior of an element or supervising the operation of an element. Thus, the "control" and similar terms in this document can, for example, refer to imposing behavior on an element (determining behavior or supervising the operation of an element), such as, for example, measuring, displaying, actuating, opening, moving, changing temperature, etc. In addition to this, the term "control" and similar terms can additionally include monitoring. Thus, the term "control" and similar terms can include imposing behavior on an element, as well as imposing behavior on an element and monitoring that element. The control of the element can be accomplished with a control system, which can also be designated as a "controller". Thus, the control system and the element can be functionally coupled at least temporarily or permanently. The element can include the control system. In an embodiment, the control system and the element can not be physically coupled. The control can be accomplished via wired and / or wireless control. The term "control system" can also refer to a plurality of different control systems, which are in particular functionally coupled, and where, for example, one of the control systems can be a main control system, and one or more other control systems can be slave control systems. The control system can include or can be functionally coupled to a user interface.

[0154] The control system can also be configured to receive and execute instructions from a remote control. In an embodiment, the control system can be controlled via an App on a device - such as a portable device (such as a smart phone or an I-phone, a tablet, etc.). Thus, the device does not necessarily have to be coupled to the lighting system, but can be (temporarily) functionally coupled to the lighting system.

[0155] Thus, in an embodiment, the control system can (also) be configured to be controlled by an App on a remote device. In such an embodiment, the control system of the lighting system can be a slave control system or a control in slave mode. For example, the lighting system can be identified by a code, in particular a unique code for the corresponding lighting system. The control system of the lighting system can be configured to be controlled by an external control system, which accesses the lighting system based on the knowledge of the (unique) code (input via a user interface of an optical sensor (such as a QR code reader)). The lighting system can also include components for communicating with other systems or devices, such as based on Bluetooth, WIFI, LiFi, ZigBee, BLE or WiMAX, or other wireless technologies.

[0156] The system, apparatus, or device may perform an action in a "mode", "operating mode", or "mode of operation". Similarly, in a method, an action, stage, or step may be performed in a "mode", "operating mode", "mode of operation", or "operable mode". The term "mode" may also be referred to as a "control mode". This does not exclude that the system, apparatus, or device may also be adapted to provide another control mode or multiple other control modes. Similarly, this may not exclude that one or more other modes may be performed before and / or after performing the mode.

[0157] However, in an embodiment, a control system may be available that is adapted to provide at least a control mode. If other modes are available, the selection of such a mode may be performed particularly via a user interface, although other options - such as performing a mode based on a sensor signal or a (time) schedule - may also be possible. In an embodiment, the operating mode may also refer to a system, apparatus, or device that can only operate in a single operating mode (i.e., "on", without additional tunability).

[0158] Thus, in an embodiment, the control system may be controlled based on one or more of an input signal of a user interface, a sensor signal (of a sensor), and a timer. The term "timer" may refer to a clock and / or a predetermined time schedule. BRIEF DESCRIPTION OF THE DRAWINGS

[0159] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, and in which:

[0160] Figure 1 Aspects of luminescent particles are schematically depicted;

[0161] Figures 2a - 2b schematically depict some additional aspects of luminescent particles;

[0162] Figure 3 A lighting device is schematically depicted;

[0163] Figures 4a - 4b show SEM and TEM images of luminescent particles;

[0164] Figures 5a - 5b show some experimental results in which embodiments of the present invention are compared with prior art luminescent materials;

[0165] Figure 6a - Figure 6b Schematic cross-sectional and top views of a pcLED array are shown respectively;

[0166] Figure 7a A schematic top view of an electronic board on which a pcLED array can be mounted is shown, andFigure 7b Similarly shown is a pcLED array mounted on Figure 7a an electronic board;

[0167] Figure 8a A schematic cross-sectional view of the pcLED array arranged relative to a waveguide and a projection lens is shown. Figure 8b Shown is a Figure 8a arrangement similar to the arrangement of

[0168] Figure 9 An example camera flash system including an adaptive illumination system is schematically shown;

[0169] Figure 10 An example display (e.g., AR / VR / MR) system including an adaptive illumination system is schematically shown.

[0170] Schematic drawings are not necessarily to scale. Detailed Description

[0171] Figure 1 An embodiment of the luminescent particle 100 is schematically depicted. The luminescent particle 100 includes a luminescent core 102, and the luminescent core 102 includes a primer layer 105 on the luminescent core 102. Here, the luminescent core 102 with the primer layer 105 is also referred to as including the primer layer 105 of the luminescent particle 100. The chemical composition of the primer layer 105 is different from that of the core 102. The luminescent core 102 may include, for example, micron-sized luminescent nitride or sulfide phosphor particles, but may also include other (smaller) materials, such as luminescent nanoparticles (see further Fig. 2b).

[0172] The luminescent particle 100 further includes a main ALD coating 120. In the shown embodiment, the main ALD coating 120 includes a multilayer 1120 having three layers 1121 (layer 1121a, layer 1121b, and layer 1121c). The three layers 1121a, 1121b, 1121c particularly have (at least two) different chemical compositions. In particular, the adjacent (and contacting) layers 1121 have different compositions. Additionally, one or more of the layers 1121 of the multilayer 1120 may have a chemical composition that is also different from that of the primer layer 105. In an embodiment, the layer 1121 may include, for example, different oxides of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V. Additionally or alternatively, the layer 1121 may include Si and / or Ge. In particular, one of the layers 1121 may be an alumina layer.

[0173] The luminescent particle 100 further includes a main sol-gel coating 130, which in particular has a chemical composition different from that of one or more layers 1121 of the multilayer 1120. The figure also shows that the main ALD coating 120 is arranged between the primer layer 105 and the main sol-gel layer 130. In particular, adjacent coatings in arrangement / contact may have different compositions. In the depicted figure, layer 1121a in particular has a composition different from that of the main sol-gel layer 130. Layer 1121c in particular has a composition different from that of the primer layer 105. Thus, Figure 1 The hybrid coating of the example in [reference] includes a primer layer 105, a main ALD layer 120, and a main sol-gel coating 130. In a further example, referring to, for example, FIG. 2a, the hybrid coating further includes another ALD coating 140.

[0174] The example of FIG. 2a further includes another ALD coating 140 arranged on the main sol-gel coating 130. In the depicted example, the other ALD coating 140 also includes another multilayer 1140, and the other multilayer 1140 includes two (other sub) layers 1141 (1141a, 1141b) of the other multilayer 1140. However, in other examples, the other ALD coating 140 is (deposited as) a single layer. In FIG. 2a, the thicknesses of the layers are also shown. Note that the thicknesses are not drawn to scale and are only for explaining the meaning of the terms and showing the positions. The primer layer thickness is denoted by the reference numeral d1. The primer layer thickness d1 may be in the range of 0.1 - 5 nm. The ALD coating thickness is denoted by the reference numeral d2. The ALD coating thickness d2 can in particular be in the range of 5 - 250 nm. The thickness of the main sol-gel coating 130 is denoted by the reference numeral d3. The main sol-gel coating thickness d3 is generally greater than the ALD coating thickness d2. The main sol-gel coating thickness d3 is in particular in the range of 50 - 700 nm. The depicted example includes a multilayer 1120 having three layers 1121, and each layer 1121 has a coating thickness d21 in the range of 1 - 20 nm. In the depicted example, the layer coating thicknesses d21 of the three layers 1121 are substantially the same. However, the layer coating thickness d21 may vary between different layers 1121, for example, referring to FIG. 4b. The three layers 1121a, 1121b, and 1121c may depict, for example, alternating Al 2 O 3 layers (as an example 1121b) and Ta 2 O 5 layers (as examples 1121a, 1121c). The (other sub) layer coating thickness of the (other sub) layer 1141 of the other multilayer 1140 (not denoted by a reference numeral) can in particular be in the range described for the layer coating thickness d21 of the layer 1121 of the multilayer 1120.

[0175] FIG. 2a further schematically depicts that the primer layer 105 includes an oxide-containing layer 101 and a primary sol-gel layer 110. The oxide-containing layer 101 is disposed at the surface 67 of the core 102. In this embodiment, the oxide-containing layer 101 and the primary sol-gel layer 110 are continuous and conformal. However, in other embodiments, this may not be the case. For example, the main ALD coating 120 may contact the oxide-containing layer 101 at some positions and may even contact the surface 67 of the core at some more distant positions (while contacting the primary sol-gel layer 110 at other positions).

[0176] FIG. 2a also denotes the surfaces of the respective layers with reference numerals 17, 27, 37, 47, 57, and denotes the surface of the core 102 with reference numeral 67. As described above, the layer thicknesses described herein are especially average layer thicknesses. In particular, at least 50%, and even more particularly at least 80%, of the area of each layer has the indicated layer thickness. Thus, with respect to the thickness d2 between the reference surface 47 and the surface 37, below at least 50% of the surface 37, a layer thickness in the range of, for example, 5 - 250 nm can be found, while another less than at least 50% of the surface area 37 can find a smaller or larger thickness, but the average d2 of the main ALD coating (multi)layer 120 is in the indicated range of 5 - 250 nm. Similarly, this also applies to the other thicknesses described herein. For example, with respect to the thickness d3 between the reference surface 37 and the surface 27, this thickness can be in the range of 50 - 700 nm over at least 50% of the area of the surface 27, while others less than at least 50% of the surface 27 can find a smaller or larger thickness, but the average d1 of the first main sol-gel layer 130 is in the indicated range of 50 - 700 nm (for example, especially 100 - 500 nm).

[0177] FIG. 2b schematically depicts an embodiment in which the luminescent core 102 includes luminescent nanoparticles, here as an example quantum dots 160. The quantum dots in this example include quantum rods having a (semiconductor) core material 161 (such as ZnSe) and a shell 162 (such as ZnS). Of course, other luminescent nanoparticles can also be used. Such luminescent quantum dots 160 can also be provided with a hybrid coating.

[0178] Figure 1 - FIG. 2 schematically depicts a luminescent particle 100 having a single core. Optionally, however, aggregates encapsulated with a hybrid coating can also be formed. This may be particularly applicable to quantum dots as the luminescent particles defining the luminescent core 102.

[0179] The drawings specifically depict an embodiment of the coating structure on the phosphor particles or luminescent nuclei 102 (after applying the corresponding (ALD and sol-gel) coating processes). The phosphor particles 102 can be covered by an oxide layer 101 formed by a washing and baking process. In an embodiment, the primary sol-gel coating 110 includes silicon oxide (SiO 2 ) provided by the (primary) sol-gel coating process. The first SiO 2 layer 110 particularly serves as a nucleation or seed layer for the main ALD coating 120 provided by the atomic layer deposition process. Thus, the (primary layer 105 and) primary sol-gel coating 110 do not need to form a conformal or completely closed coating around each nucleus 102. The primary sol-gel coating 110 (such as the primary SiO 2 layer 110) can also be regarded as a surface treatment that provides OH-groups on the phosphor particles 102. Such OH-groups can help the ALD precursors bind to the surface and thus initiate film growth.

[0180] The main ALD coating 120 particularly includes a multi-layer 1120 of metal oxide (sub-) layers 1121, also referred to as a "nanolaminate" 1120. The nanolaminate 1120 can form a very dense and almost pinhole-free conformal coating on the phosphor particles, and this conformal coating hardly permeates gases such as water vapor and oxygen. In an embodiment, the nanolaminate protective layer 1120 can have a thickness d2 of 20 - 50 nm, and is composed of more than two sub-layers of Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , SnO 2 , ZnO or Ta 2 O 5 . Each layer 1121 can have a thickness d21 in the range of 1 nm - 15 nm. The outer layer 1121, that is, the layer in contact with the main sol-gel coating 130 ( Figure 1 and 1121a in Figure 2a), is a chemically stable layer (such as HfO 2 , ZrO 2 or Ta 2 O 5 ) in an embodiment, which does not corrode when exposed to water or other solvents (such as cyclohexanone).

[0181] The main sol-gel coating 130 can also include silicon oxide (SiO 2), similar to the primary sol-gel coating 110. The primary sol-gel coating 130 can particularly serve as mechanical protection to prevent damage to the underlying barrier coating 120. In the LED manufacturing process, the phosphor particles undergo various process steps such as mixing, sieving, pressing, and shaping. These process steps may cause mechanical stress in the coating. As a result, the coating may be damaged. The primary sol-gel coating 130 provides high robustness against post-treatment and manufacturing steps. In an embodiment, high reliability can be ensured by applying a layer of the primary sol-gel coating 130 on the luminescent particles 100.

[0182] In an embodiment of the present invention, as shown in FIG. 2a, another ALD coating 140 is added to the layer structure. The another ALD coating 140 in this embodiment includes a nano-laminate 1140. The layer 140 or the multi-layers 1140 may include metal oxides such as Al 2 O 3 、TiO 2 、ZrO 2 、HfO 2 、SnO 2 、ZnO or Ta 2 O 5 。The total thickness d4 of the layer 140 is particularly in the range of 10 - 50 nm. The another ALD coating 140 can further stabilize the entire coating structure by filling the pores and pinholes in the primary sol-gel coating 130. In addition, the another ALD coating 140 can inhibit the surface reactivity of the primary sol-gel layer 130. In an embodiment of the LED manufacturing process, this surface reactivity may be beneficial for maintaining the rheology or other properties of certain silicone phosphor slurries.

[0183] Figure 3Schematically depicts a lighting device 20, which includes a light source 10 and a wavelength converter 30. The light source 10 is configured to generate light source radiation 11 (in particular one or more of blue and UV), and the wavelength converter 30 includes a luminescent material 1 having particles 100 as defined herein. The wavelength converter 30 may, for example, include a matrix, such as a silicone or organic polymer matrix as described above, in which the coated particles 100 are embedded. The wavelength converter 30 is configured to convert at least a portion (wavelength) of the light source radiation 11 into wavelength converter light 31. Optionally, the light source radiation 11 may also pass through the wavelength converter 30 (without being converted). The wavelength conversion light 31 at least includes luminescence from the coated particles 100 described herein. However, the wavelength converter 30 may optionally also include one or more other luminescent materials. The wavelength converter 30 (or more particularly the luminescent material 1) may be disposed at a non-zero distance d30, for example, at a distance of 0.1 - 100 mm. However, optionally, the distance d30 may be zero, such as, for example, when the luminescent material is embedded in a dome on an LED die. The distance d30 is the shortest distance between the light-emitting surface of the light source 10 (e.g., an LED die) and the wavelength converter 30 (more specifically the luminescent material 1).

[0184] The light source 10 may be an LED, such that the lighting device 20 is a phosphor-converted LED (“pcLED”). For example, the light source 10 may be a group III nitride LED that emits ultraviolet light, blue light, green light, or red light. LEDs formed of any other suitable material system and emitting light of any other suitable wavelength may also be used. Other suitable material systems may include, for example, group III phosphide materials, group III arsenide materials, and II-VI materials.

[0185] Figure 4a shows an SEM image of the luminescent material 1 including some coated luminescent particles 100. In Figure 4b, a TEM image of the coated luminescent particles 100 is given, which clearly shows a core 102 having an oxide-containing layer 101, a primary (SiO 2 ) sol-gel coating 110, a main ALD coating 120 (including a multilayer 1120 composed of two Al 2 O 3 layers 1121b and two Ta 2 O 5 layers 1121a) and a main (SiO 2 ) sol-gel coating 130.

[0186] Figures 5a - 5b show some experimental results. In the drawings, the coated luminescent particles 100 of the present invention (here containing SrLiAl 3 N 4:Eu) and compared with the corresponding prior art luminescent particles. The prior art luminescent particles also include an ALD coating and a sol-gel coating. However, the sol-gel coating is directly disposed on the surface of the luminescent core 102, and the ALD coating is disposed on the sol-gel coating.

[0187] In FIG. 5a, the (normalized) light output (Y-axis) of individual luminescent particles in silicone as a function of time, particularly in hours (X-axis), is given. During the experiment, the particles were kept at 130° C. and 100% relative humidity. The circular markers represent the luminescent particles 100 of the present invention; the square markers represent the prior art luminescent particles.

[0188] In FIG. 5b, the failure probability of white LEDs with the corresponding luminescent particles is given after keeping the corresponding LEDs at 85° C. and 85% relative humidity for more than 500 hours. The square markers represent the luminescent particles 100 of the present invention; the circular markers represent the prior art luminescent particles. Note that the probability is given as a percentage on the Y-axis on a logarithmic scale. The chromaticity shift, denoted by Δu'v' (sometimes also denoted as “(du'v')” or “duv”), is given on the X-axis. The luminescent particles 100 of the present invention (including the LEDs with the luminescent particles 100) clearly show less chromatic shift (Δu'v' is calculated as the Euclidean distance between a pair of chromaticity coordinates in the (u', v') CIE 1976 color space).

[0189] Accordingly, the present invention relates to a method for improving the barrier properties of phosphor particle coatings. While the present invention is generally applicable to various phosphor particles, due to their high sensitivity to moisture, the present invention is particularly applicable to nitride-based narrow-band red-emitting phosphors, such as aluminate nitrides or oxynitride aluminates.

[0190] FIGS. 6A - 6B respectively show a cross-sectional view and a top view of an array 600 of pcLEDs 610, which can be constructed as the Figure 3 illustrated lighting device 20, which includes a wavelength converter 30 that includes coated luminescent particles 100 contained in phosphor pixels 606 as defined herein, wherein a semiconductor diode 612 is disposed on a substrate 602. Such an array can include any suitable number of pcLEDs arranged in any suitable manner. In the illustrated example, the array is depicted as being formed monolithically on a shared substrate, but alternatively, a pcLED array can be formed from separate individual pcLEDs. The substrate 602 can optionally include CMOS circuitry for driving the LEDs and can be formed of any suitable material.

[0191] Although FIGS. 6A-6B illustrate a three-by-three array of nine pcLEDs, such arrays can include, for example, dozens, hundreds, or thousands of LEDs. Each LED (pixel) can have a width (e.g., side length) in the plane of the array that is, for example, less than or equal to 1 millimeter (mm), less than or equal to 500 micrometers, less than or equal to 100 micrometers, or less than or equal to 50 micrometers. The LEDs in such an array can be separated from each other by streets or lanes having a width in the plane of the array that is, for example, hundreds of micrometers, less than or equal to 100 micrometers, less than or equal to 50 micrometers, less than or equal to 10 micrometers, or less than or equal to 5 micrometers. While the illustrated examples show rectangular pixels arranged in a symmetric matrix, these pixels and arrays can have any suitable shape or arrangement.

[0192] LEDs in the plane of the array having dimensions (e.g., side length) less than or equal to about 50 micrometers are generally referred to as microLEDs, and an array of such microLEDs can be referred to as a microLED array.

[0193] An array of LEDs or portions of such an array can be formed as a segmented monolithic structure, where each LED pixel is electrically isolated from the others by trenches and / or insulating materials, but the electrically isolated segments are physically connected to each other through portions of the semiconductor structure.

[0194] Each LED in the LED array can be individually addressable, addressable as part of a group or subset of pixels in the array, or not addressable. Thus, an array of light-emitting pixels is useful for any application that requires or benefits from fine-grained intensity, spatial, and temporal control of light distribution. These applications can include, but are not limited to, precise special patterning of the emitted light from pixel blocks or individual pixels. Depending on the application, the emitted light can be spectrally distinct, time-adaptive, and / or environment-responsive. Such an array of light-emitting pixels can provide a pre-programmed light distribution in various intensity, spatial, or temporal patterns. The emitted light can be at least partially based on received sensor data and can be used for optical wireless communication. The associated electronics and optics can be distinct at the pixel, pixel block, or device level.

[0195] As shown in FIGS. 7A-7B, a pcLED array 600 can be mounted on an electronic board 700 that includes a power and control module 702, a sensor module 704, and an LED attachment area 706. The power and control module 702 can receive power and control signals from an external source as well as signals from the sensor module 704, and the power and control module 702 controls the operation of the LEDs based on these signals. The sensor module 704 can receive signals from any suitable sensor (e.g., from a temperature or light sensor). Alternatively, the pcLED array 600 can be mounted on a separate board (not shown) from the power and control module and the sensor module.

[0196] Optionally, each pcLED can include a lens or other optical element, or be arranged in combination with a lens or other optical element, which is positioned adjacent to or disposed on the phosphor layer. Such an optical element (not shown in the figures) can be referred to as a "primary optical element". Additionally, as shown in FIGS. 8A-8B, the pcLED array 600 (e.g., mounted on the electronic board 700) can be arranged in combination with a secondary optical element (such as a waveguide, a lens, or both) for use in an intended application. In FIG. 8A, the light emitted by the pcLED 610 is collected by the waveguide 802 and directed to the projection lens 804. For example, the projection lens 804 can be a Fresnel lens. For example, this arrangement can be suitable for use in vehicle headlights. In FIG. 8B, the light emitted by the pcLED 610 is directly collected by the projection lens 804 without using an intervening waveguide. This arrangement can be particularly suitable when the pcLEDs can be spaced close enough to each other, and can also be used in vehicle headlights as well as camera flash applications. For example, microLED display applications can use an optical arrangement similar to the optical arrangements depicted in FIGS. 8A-8B. Generally, depending on the desired application, any suitable arrangement of optical elements can be used in combination with the LED arrays described herein.

[0197] Independently operable LED arrays can be used in combination with lenses, lens systems, or other optical systems (e.g., as described above) to provide illumination suitable for a particular purpose. For example, in operation, such an adaptive lighting system can provide illumination that varies in color and / or intensity over an illuminated scene or object, and / or is aimed in a desired direction. The controller can be configured to receive data indicating the position and color characteristics of an object or person in the scene, and control the LEDs in the LED array based on this information to provide illumination suitable for the scene. Such data can be provided by, for example, an image sensor, an optical (e.g., laser scanning) or non-optical (e.g., millimeter wave radar) sensor. Such adaptive lighting is becoming increasingly important for vehicle, mobile device camera, VR, and AR applications.

[0198] Figure 9 FIG. 900 schematically shows an example camera flash system 900 including an LED array and a lens system 902, which may be similar or identical to the above-described systems. The flash system 900 also includes an LED driver 906 controlled by a controller 904 (e.g., a microprocessor). The controller 904 may also be coupled to a camera 907 and a sensor 908 and operates according to instructions and profiles stored in a memory 910. The camera 907 and the adaptive illumination system 902 may be controlled by the controller 904 to match their fields of view.

[0199] The sensor 908 may include, for example, a position sensor (e.g., a gyroscope and / or an accelerometer) and / or other sensors that may be used to determine the position, velocity, and orientation of the system 900. Signals from the sensor 908 may be provided to the controller 904 for determining an appropriate course of action for the controller 904 (e.g., which LEDs are currently illuminating a target and which LEDs will illuminate the target after a predetermined amount of time).

[0200] In operation, the illumination of some or all pixels of the LED array in 902 may be adjusted - deactivated, operated at full intensity, or operated at an intermediate intensity. Beam focusing or steering of the light emitted by the LED array in 902 may be electronically performed by activating one or more subsets of pixels to allow for dynamic adjustment of the beam shape without moving the optics or changing the focus of the lenses in the illumination device.

[0201] Figure 10 FIG. 1000 schematically shows an example display (e.g., AR / VR / MR) system 1000, which includes an adaptive light emitting array 1010, a display 1020, a light emitting array controller 1030, a sensor system 1040, and a system controller 1050. Control inputs are provided to the sensor system 1040, while power and user data inputs are provided to the system controller 1050. In some embodiments, the modules included in the system 1000 may be compactly arranged in a single structure, or one or more elements may be separately mounted and connected via wireless or wired communication. For example, the light emitting array 1010, the display 1020, and the sensor system 1040 may be mounted on a headset or glasses, where the light emitting controller and / or the system controller 1050 are separately mounted.

[0202] The light emitting array 1010 may include one or more adaptive light emitting arrays, as described above, e.g., which may be used to project light in a pattern of graphics or objects that can support an AR / VR / MR system. In some embodiments, a micro LED array may be used.

[0203] System 1000 may incorporate a variety of optical devices in the adaptive light emitting array 1010 and / or the display 1020, such as coupling the light emitted by the adaptive light emitting array 1010 into the display 1020.

[0204] The sensor system 1040 may include, for example, external sensors such as cameras, depth sensors, or audio sensors that monitor the environment, and internal sensors such as accelerometers or two-axis or three-axis gyroscopes that monitor the position of the AR / VR / MR headset. Other sensors may include, but are not limited to, barometric sensors, stress sensors, temperature sensors, or any other suitable sensors required for local or remote environmental monitoring. In some embodiments, the control input may include detected touches or taps, gesture inputs, or controls based on the position of the headset or display.

[0205] In response to data from the sensor system 1040, the system controller 1050 may send images or instructions to the light emitting array controller 1030. Changes or modifications to the images or instructions may also be made through user data input or automated data input as needed. User data input may include, but is not limited to, data input provided by audio instructions, haptic feedback, eye or pupil positioning, or a connected keyboard, mouse, or game controller.

[0206] In one embodiment, the present invention provides a wet chemical washing (including drying) process for powder phosphors ((multiple) luminescent nuclei) to form an outer oxide particle layer. Additionally, a primary (SiO 2 ) sol-gel layer may be deposited by a (primary) sol-gel process to provide a primary sol-gel layer having a thickness in the range of 0.5 - 5 nm. Next, multiple layers may be deposited by ALD, where in an embodiment the total ALD coating thickness d2 is 20 - 50 nm, and the (sub) layer thickness d21 of the layers 1121 of the multiple layers 1120 is in the range of 1 - 20 nm. The multiple layers 1120 particularly include two or more metal oxides, such as Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , SnO 2 , ZnO, Ta 2 O 5 . Next, a third layer - particularly a primary sol-gel coating 130, such as SiO 2—— can be deposited by a (main) sol - gel process, with a thickness in the range of 100 - 500 nm. In yet another embodiment, the fourth layer 140 can be deposited by an additional ALD process. In an embodiment, another ALD coating 140 can have a total thickness d4 of 5 - 50 nm and can in particular comprise multiple layers with sub - layer thicknesses in the range of 1 - 20 nm. In an embodiment, the multiple layers are composed of one or more metal oxides, such as Al 2 O 3 、TiO 2 、ZrO 2 、HfO 2 、SnO 2 、ZnO、Ta 2 O 5 。

[0207] Experiment

[0208] The effects of the new coating structure of the present invention are tested by forming luminescent particles with the hybrid coatings disclosed herein:

[0209] Polyol washing process:

[0210] 10.3 grams of the raw phosphor powder sample with the composition Sr 0.995 Li 2 Al 1.995 Si 0.005 O 1.995 N 2.005 :Eu 0.005 is mixed with 30.0 grams of ethanol and 30.0 g of triethylene glycol. The suspension shows a total water content in the range of 0.05 - 0.1% in an ultrasonic bath and is then treated at 80 °C for 16 hours in a closed pressure vessel. After cooling to room temperature, the phosphor powder is washed with ethanol and dried at 100 °C in ambient atmosphere.

[0211] Mixed solvent acetic acid washing process:

[0212] 200 - 250 grams of SrLiAl 3 N 4 :Eu 0.007 is stirred in 837 grams of isopropanol. 560 grams of 18.5 wt% acetic acid is slowly added under stirring. The suspension is further stirred until a total time of 40 minutes (including the addition of the acid). After 30 minutes of sedimentation, most of the supernatant is removed by decantation, and then filtered and rinsed with an acetic acid / isopropanol mixture and isopropanol. The washed phosphor is finally dried in vacuo at 50 °C overnight.

[0213] Thin amorphous silica layer (<5 nm):

[0214] In this experiment, a primary sol-gel coating was provided. 200 g of phosphor powder (usually after washing) was stirred in 960 g of ethanol. 3.5 g of tetraethyl orthosilicate was added to the suspension and stirred under ultrasound for 10 minutes. 90 g of 25 wt% ammonia water solution was added and stirring was continued under ultrasound for another 20 minutes. Fine particles including nano-sized silica particles formed as by-products were removed by triple sedimentation and decantation in ethanol. The coated powder was dried overnight in vacuum at 50 °C. After dry sieving (mesh size 100 μm), the coating was cured by heating the powder to 300 °C in vacuum for 10 hours.

[0215] ALD nano-laminate (~25 nm):

[0216] Next, in a Picosun Oy ALD R200 reactor, a main ALD coating containing the ALD nano-laminate was coated on a primer layer containing phosphor particles (containing SrLiAl 3 N 4 :Eu). The precursor materials were trimethylaluminum and H 2 O to form an Al 2 O 3 film, and (tert-butylimino)tris(diethylmethylamino)tantalum(V) and H 2 O to form a Ta 2 O 5 film. The deposition temperature was set at 250 °C. The nitrogen purge time between precursor pulses was 60 seconds. The nano-laminate consisted of 2x Al 2 O 3 / Ta 2 O 5 sub-layers with a total thickness of about 25 nm.

[0217] Thick amorphous silica layer (~170 nm):

[0218] In this experiment, a main sol-gel coating was provided on the luminescent particles. 85 g of powder (usually after ALD coating) was ultrasonically stirred in 672 g of ethanol for 15 minutes. To this suspension, 1) 116 g of 25 wt% ammonia water solution was added rapidly (<30 seconds), and 2) a solution of 68 g of tetraethyl orthosilicate in 408 g of ethanol was added dropwise (~45 minutes). After the addition of the alkoxide precursor was completed, the suspension was stirred for another 30 minutes without ultrasound.

[0219] Fine particles including sub-micron sized silica particles formed as by-products were removed by triple sedimentation and decantation in ethanol. The coated powder was dried overnight in vacuum at 50 °C. After dry sieving (mesh size 63 μm), the coating was cured by heating the powder to 300 °C in vacuum for 10 hours.

[0220] SEM images of some particles are given in Fig. 4a. TEM images of the particles are given in Fig. 4b.

[0221] Comparative tests

[0222] The particles prepared in silicone were subjected to stress tests and compared with control particles (i.e., particles containing a prior art coating structure). In the prior art coating structure, the luminescent particles were initially coated with a relatively thick sol-gel coating and subsequently with a thin ALD coating. In the stress test, the particles were held at a temperature of 130 °C and a relative humidity of 100%, and the change in light output over time was measured.

[0223] The prepared particles were further applied to white LEDs and stressed at 85 °C and 85% relative humidity for over 500 hours. The failure probability of the white LEDs with the luminescent particles according to the present invention was compared with the failure probability of white LEDs (control LEDs) including a prior art coating structure that had undergone the same stress test.

[0224] The results are depicted in Figs. 5a - 5b, which show a significantly improved reduction in light output after a 60-hour stress test, i.e., less than 5% compared to a reduction of over 50% for the control particles. In addition, the color shift (Δu'v') was substantially minimized compared to the control LEDs.

[0225] The term "plurality" refers to two or more.

[0226] Those skilled in the art will understand the terms "substantially" or "essentially" and similar terms herein. The terms "substantially" or "essentially" can also include embodiments with "completely", "fully", "entirely", etc. Thus, in an embodiment, the adjectives substantially or essentially can also be removed. Where applicable, the term "substantially" or the term "essentially" can also refer to 90% or higher, such as 95% or higher, particularly 99% or higher, and even more particularly 99.5% or higher, including 100%.

[0227] The term "comprising" also includes embodiments where the term "comprising" means "consisting of".

[0228] The term "and / or" particularly relates to one or more of the items mentioned before and after "and / or". For example, the phrase "item 1 and / or item 2" and similar phrases can relate to one or more of item 1 and item 2. The term "comprising" can mean "consisting of" in one embodiment, but can also mean "including at least the defined species and optionally one or more other species" in another embodiment.

[0229] In addition, the terms first, second, third, etc. in the specification and claims are used to distinguish between similar elements and are not necessarily used to describe an order or a temporal sequence. It should be understood that the terms so used are interchangeable under appropriate circumstances, and the embodiments of the invention described herein are capable of operating in an order different from that described or illustrated herein.

[0230] During operation, a device, apparatus or system may be described herein, among other things. As will be apparent to those skilled in the art, the invention is not limited to the method of operation, or the device, apparatus or system in operation.

[0231] It should be noted that the above embodiments illustrate rather than limit the invention, and those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

[0232] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

[0233] The use of the verb "comprise" and its variants does not exclude the presence of elements or steps other than those stated in the claim. Throughout the specification and claims, the words "comprise", "comprising", etc. shall be interpreted in an inclusive sense rather than an exclusive or exhaustive sense; that is, in the sense of "including but not limited to".

[0234] The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0235] The present invention can be implemented by means of hardware including several different elements and by means of a suitably programmed computer. In a device claim, an apparatus claim or a system claim listing several components, several of these components may be embodied by the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously.

[0236] The present invention also provides a control system which can control a device, an apparatus or a system, or can execute a method or process described herein. Still further, the present invention also provides a computer program product which, when run on a computer functionally coupled to or included in a device, an apparatus or a system, controls one or more controllable elements of such device, apparatus or system.

[0237] The present invention is also applicable to a device, an apparatus or a system including one or more features described in the specification and / or shown in the accompanying drawings. The present invention also relates to a method or process including one or more features described in the specification and / or shown in the accompanying drawings.

[0238] The various aspects discussed in this patent can be combined to provide additional advantages. In addition, those skilled in the art will understand that the embodiments can be combined, and more than two embodiments can also be combined. In addition, some features can form the basis for one or more divisional applications.

Claims

1. A method for providing a hybrid coating for luminescent particles, the method comprising: (i) providing a particulate luminescent material having a surface; (ii) directly forming a primer layer on at least a portion of the surface, the primer layer comprising an oxide-containing layer and having a thickness greater than or equal to 0.1 nm and less than 5 nm, wherein directly forming the primer layer on at least a portion of the surface comprises performing a primer sol-gel coating process on the particulate luminescent material, the primer sol-gel coating process using a metal alkoxide precursor, wherein the metal alkoxide precursor is a silanolate; (iii) performing a first atomic layer deposition process on the particulate luminescent material having the primer layer to deposit a first ALD layer, the first atomic layer deposition process using a first metal oxide precursor selected from one of the metal oxides comprising Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V; (iv) performing a second atomic layer deposition process to deposit a second ALD layer onto the first ALD layer, the second atomic layer deposition process using a second metal oxide precursor different from the first precursor and selected from one of the metal oxides comprising Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V; and (v) performing a main sol-gel coating process to directly form a main sol-gel coating on the second ALD layer, the main sol-gel coating having a chemical composition different from that of the first ALD layer and the second ALD layer.

2. The method according to claim 1, wherein the primer sol-gel coating process comprises: suspending the particulate luminescent material in an alcohol-ammonia aqueous solution mixture; adding the metal alkoxide precursor to the mixture; stirring the mixture containing the metal alkoxide until the primer layer is formed; washing the particulate luminescent material having the primer layer with alcohol; and drying the particulate luminescent material having the primer layer.

3. The method according to claim 1, further comprising washing the particulate luminescent material in a washing solvent having a pH < 7 before forming the primer layer.

4. The method according to claim 3, wherein the washing solvent comprises an organic acid.

5. The method according to claim 3, wherein the washing solvent comprises a fatty alcohol.

6. The method according to claim 3, wherein the washing solvent comprises a weak acid and water equal to or less than 50% wt / wt, and washing the particulate luminescent material further comprises: continuously drying the particulate luminescent material.

7. The method according to claim 1, wherein the primer layer comprises a primary sol-gel layer provided by applying a primary sol-gel coating process.

8. The method according to claim 1, wherein: (i) the first ALD layer and the second ALD layer form a main ALD coating, and the main ALD coating has a main ALD coating thickness d2 in the range of 5 - 250 nm; and (ii) The main sol-gel coating has a main sol-gel coating thickness d3 in the range of 50 - 700 nm.

9. The method according to claim 1, wherein the first metal oxide precursor is Al, and the second metal oxide precursor is selected from one of the metal oxides including Hf, Ta, Zr, and Ti.

10. The method according to claim 1, wherein the main sol-gel coating process comprises: providing a mixture of an alcohol, ammonia, water, a particulate luminescent material having the primer layer, the first ALD layer, and the second ALD layer, and a metal alkoxide precursor, while stirring the mixture and allowing the main sol-gel coating to form directly on the second ALD layer, the metal alkoxide precursor being a titanium alkoxide, a silicon alkoxide, and / or an aluminum alkoxide; and retrieving the particulate luminescent material having the primer layer, the first ALD layer, the second ALD layer, and the main sol-gel coating from the mixture, and heat-treating the retrieved particulate luminescent material having the primer layer, the first ALD layer, the second ALD layer, and the main sol-gel coating.

11. The method according to claim 1, wherein in the main sol-gel coating process, a silicon alkoxide precursor is used, and the silicon alkoxide precursor is selected from one or more of the following And in the first atomic layer deposition process and the second atomic layer deposition process, a metal oxide first precursor and a metal oxide second precursor selected from one or more of Al(CH 3 ) 3 , HAl(CH 3 ) 2 , Hf(N(CH 3 ) 2 ) 4 , Hf(N(CH 2 CH 3 ) 2 ) 4 , Hf[N(CH 3 )(CH 2 CH 3 )] 4 , TaCl 5 , Ta(N(CH 3 ) 2 ) 5 , Ta{[N(CH 3 )(CH 2 CH 3 )] 3 N(C(CH 3 ) 3 )}, ZrCl 4 , Zr(N(CH 3 ) 2 ) 4 , TiCl 4 , Ti(OCH 3 ) 4 , and Ti(OCH 2 CH 3 ) 4 , and an oxygen source selected from one or more of H 2 O and O 3 .

12. The method according to claim 1, comprises: Provide n additional ALD layers continuously, where 2 ≤ n ≤ 10, between the first ALD layer and the second ALD layer. Each additional ALD layer has an additional ALD layer coating thickness d21 in the range of 1 - 20 nm. One or more of the additional ALD layers include one or more metal oxides selected from the group of HfO 2 、ZrO 2 、TiO 2 、Ta 2 O 5 . One or more of the additional ALD layers include Al 2 O 3 , and the second ALD is composed of one or more metal oxides selected from the group of HfO 2 、ZrO 2 、TiO 2 、Ta 2 O 5 .

13. The method according to claim 1, further comprises: providing another ALD coating on the main sol-gel coating by applying another atomic layer deposition process, in which another metal oxide precursor is selected from one of the metal oxides including Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V, the another ALD coating has another ALD coating thickness d4 in the range of 10 - 50 nm, and the another ALD coating has a chemical composition different from that of the main sol-gel coating.

14. The method according to claim 13, wherein said further ALD coating comprises two or more layers having different chemical compositions, and one or more of said layers comprises one or more metal oxides selected from the group consisting of Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , SnO 2 , ZnO and Ta 2 O 5 , and said two or more layers have a chemical composition different from that of said main sol-gel coating.

15. The method according to claim 1, wherein the surface of the particulate luminescent material comprises an alkaline earth element, aluminum, and an oxide.

16. The method according to claim 15, wherein the alkaline earth element comprises strontium.

17. The method according to claim 1, wherein the particulate luminescent material is selected from one or more of the following: (M1)Li d Mg a Al b N 4 :Eu, where 0 ≤ a ≤ 4, 0 ≤ b ≤ 4, 0 ≤ d ≤ 4, and M1 includes one or more selected from the group consisting of Ca, Sr, and Ba, and a + b + d = 4 and 2a + 3b + d = 10; and (M2)Li 2 Al 2-z Si z O 2-z N 2+z :Eu, where 0 ≤ z ≤ 0.1, and M2 comprises one or more of the group consisting of Sr and Ba.

18. The method according to claim 1, wherein the particulate luminescent material is selected from the group consisting of (i) SrLiAl 3 N 4 :Eu 2+ class and (ii) SrLi 2 Al 1.995 Si 0.005 O 1.995 N 2.005 :Eu 2+ classes.

19. The method according to claim 1, wherein the particulate luminescent material has a number average particle size in the range of 0.1 - 50 μm.

20. A luminescent material comprising luminescent particles obtained by the method according to claim 1.

21. A luminescent material, comprises: a particulate luminescent material having a surface; A primer layer, which is disposed on the surface of the particulate luminescent material and in contact with the surface of the particulate luminescent material, the primer layer being a primer layer metal oxide and having a thickness greater than or equal to 0.1 nm and less than 5 nm, wherein the primer layer metal oxide comprises SiO 2 ; A first ALD layer, which is disposed on any part of the primer layer and the surface of the particulate luminescent material not covered by the primer layer and is in contact with the primer layer and any part of the surface of the particulate luminescent material not covered by the primer layer, the first ALD layer comprising a first oxide of one or more of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V and being different from the primer layer metal oxide; A second ALD layer, which is disposed on the first ALD layer and in contact with the first ALD layer, the second ALD layer comprising a second oxide of one or more of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V and being different from the first oxide, the first ALD layer and the second ALD layer forming a main ALD layer having a thickness in the range of 5 - 250 nm; and A main sol - gel coating disposed on the second ALD layer, wherein the main sol - gel coating has a main sol - gel coating thickness d3 in the range of 50 - 700 nm, and wherein the main sol - gel coating has a chemical composition different from that of the first ALD layer and the second ALD layer.

22. The luminescent material according to claim 21, wherein at least a part of the surface of the particulate luminescent material comprises an oxide.

23. The luminescent material according to claim 22, wherein at least a part of the surface of the particulate luminescent material comprises an alkaline earth element and aluminum.

24. The luminescent material according to claim 23, wherein the alkaline earth element comprises strontium.

25. The luminescent material according to claim 21, wherein the particulate luminescent material is selected from one or more of the following: (M1) Li d Mg a Al b N 4 :Eu, where 0 ≤ a ≤ 4, 0 ≤ b ≤ 4, 0 ≤ d ≤ 4, and M1 includes one or more of the group consisting of Ca, Sr, and Ba, and a + b + d = 4 and 2a + 3b + d = 10; and (M2)Li 2 Al 2-z Si z O 2-z N 2+z :Eu, where 0 ≤ z ≤ 0.1, and M2 comprises one or more of the group consisting of Sr and Ba.

26. The luminescent material according to claim 21, wherein the particulate luminescent material is selected from the group consisting of (i) SrLiAl 3 N 4 :Eu 2+ class and (ii) SrLi 2 Al 1.995 Si 0.005 O 1.995 N 2.005 :Eu 2+ classes.

27. The luminescent material according to claim 21, further comprising another ALD coating disposed on the main sol - gel coating, the another ALD coating having another ALD coating thickness d4 in the range of 10 - 50 nm, the another ALD coating having a chemical composition different from that of the main sol - gel coating, and the another ALD coating comprising one or more oxides of one or more of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V.

28. The luminescent material according to claim 27, wherein the further ALD coating comprises a further multi-layer having two or more layers, the two or more layers having different chemical compositions, and one or more of the layers comprises a metal oxide selected from the group consisting of Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , SnO 2 , ZnO and Ta 2 O 5 , and the two or more layers have chemical compositions different from the chemical composition of the main sol-gel coating.

29. The luminescent material according to claim 21, wherein the first ALD layer comprises Al 2 O 3 , and the second ALD layer comprises one or more metal oxides selected from the group consisting of HfO 2 , ZrO 2 , TiO 2 , Ta 2 O 5 .

30. The luminescent material according to claim 21, further comprising n additional ALD layers, where 2 ≤ n ≤ 10, between the first ALD layer and the second ALD layer, each additional ALD layer having an additional ALD layer coating thickness d21 in the range of 1 - 20 nm, and one or more of the additional ALD layers comprising one or more metal oxides selected from the group consisting of 2 HfO 2 ZrO 2 TiO 2 Ta 5 O of the group.

31. A lighting device, comprising a light source configured to generate light source radiation and a wavelength converter comprising the luminescent material according to claim 21, the wavelength converter being configured to convert at least part of the light source radiation into wavelength converter light.

32. The lighting device according to claim 31, wherein the particulate luminescent material comprises an alkaline earth aluminate, and the wavelength converter comprises silicone.

33. A display system, comprising: A light - emitting diode array, the light - emitting diode array comprising a plurality of phosphor - converted light - emitting diodes, each phosphor - converted light - emitting diode comprising a wavelength converter comprising the luminescent material according to claim 21; A display; and A lens or a lens system, which is spaced apart from the light - emitting diode array and is arranged to couple light from the light - emitting diode array into the display.

34. A mobile device, comprising: A camera; and A flash illumination system, comprising: a light emitting diode array including a plurality of light emitting diodes, each light emitting diode including a wavelength converter containing the light emitting material described in claim 21.

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