Thin-film wavelength converters and methods for their manufacture

Abstract

Thin film wavelength converter comprising: a substrate; a first thin film layer, wherein the first thin film layer comprises at least a first wavelength conversion material; a conductive layer; and a second thin film layer deposited on the conductive layer, the second thin film layer comprising at least a second wavelength conversion material; where: the first thin-film layer is configured to convert incident primary light from a light source in a first wavelength range into secondary light in a second wavelength range; and the second thin film layer is configured to convert at least one of the primary light and the secondary light into tertiary light in a third wavelength range, wherein the second wavelength range is different from the third wavelength range.

Description

FIELD OF INVENTION

[0001] The present application relates to thin-film wavelength converters and, in particular, to methods for fabricating thin-film wavelength conversion structures. GENERAL STATE OF THE ART

[0002] The following publications describe wavelength converters: US 2004 / 173806 A1, WO 2001 / 024283 A1, US 8093610 B2, WO 2009 / 014707 A2, EP 2270884 A1, WO 2013 / 025264 A1. The publication US 2013 / 187122 A1 describes photonic components with embedded nanostructures.

[0003] Solid-state light sources such as light-emitting diodes (LEDs) generate visible or invisible light in a specific region of the electromagnetic spectrum. For example, an LED can emit light in the blue, red, green, or UV regions of the electromagnetic spectrum, depending on the LED's material composition. If it is desired to construct an LED light source that produces light of a color different from the LED's output color, this is achieved by downconverting the emitted radiation ("primary light") from an LED source into radiation of a longer wavelength ("secondary light" and "tertiary light," as needed) by a luminescent material via the process of photoluminescence.

[0004] Photoluminescence generally involves the absorption of higher-energy radiation (photons) and the emission of radiation with longer wavelengths by a wavelength-converting material ("conversion material") such as a phosphor or a mixture of phosphors. This process may be referred to as "wavelength conversion." An LED combined with a wavelength-converting structure containing a conversion material such as a phosphor to produce secondary or tertiary light may be referred to as a "phosphor-converted LED" or "wavelength-converted LED" light source.

[0005] In one common configuration, an LED die, such as a III-nitride die, is positioned in a reflector shell package. To partially or completely convert primary light from an LED into secondary light, a wavelength-converting material must be included in a light source design. This material could be in the form of powder or a self-supporting "sheet," such as a ceramic or single-crystalline sheet. The sheet can be attached directly to the LED die by bonding, sintering, gluing, etc. Such configurations can be referred to as "chip-level conversion" or "CLC." "Chip-level conversion" also includes direct deposition of a conversion material on the LED chip or deposition of a composite material consisting of particles of conversion materials dispersed in silicone. Alternatively, the sheet can be positioned remotely from the LED.Such a configuration can be understood as a “remote conversion”.

[0006] Furthermore, it is increasingly desirable to use wavelength-converting materials that can partially or completely convert the primary light emitted by an LED into secondary and / or tertiary light to produce light with a desired correlated color temperature. In particular, there has been growing interest in fabricating wavelength-converting structures to produce "warm white" light sources, meaning that the light generated by the light source is white and has a color temperature in the range of approximately 2500-3500 K. Although warm white LED lamps have been developed using wavelength-converting structures containing one or more phosphor powders dispersed in a polymeric binder (e.g., silicone), such converters have many disadvantages.For example, the powdered phosphor in silicone can impose limitations on the thermal management of an LED lamp, which can negatively impact the lamp's performance and lifetime.

[0007] Thus, there is a need in the art for wavelength-converting structures that can generate secondary and / or tertiary light with desired optical characteristics and that can avoid some or all of the limitations of a powder phosphor in a silicone converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Reference is now made to the following detailed description, which should be read in conjunction with the following figures: Fig. 1A and Fig. 1B illustrate exemplary light sources with a wavelength converter positioned for chip-level conversion and remote conversion, respectively, according to the present disclosure. Fig. 2A-2D illustrate step-by-step an exemplary process for forming an all-inorganic wavelength converter according to the present disclosure. Fig. 3 is a flowchart illustrating exemplary operations for forming an all-inorganic wavelength converter according to Fig. 2D illustrated. Fig. 4A-4G illustrate step-by-step another exemplary process for forming an all-inorganic wavelength converter according to the present disclosure. Fig. 5 is a flowchart illustrating exemplary operations for forming an all-inorganic wavelength converter according to Fig. 4A-4G illustrates. Fig. 6A-6D illustrate step-by-step another exemplary process for forming another all-inorganic wavelength converter according to the present disclosure. Fig. 7 is a flowchart illustrating exemplary operations for forming an all-inorganic wavelength converter according to Fig. 6D illustrates. Fig. 8A-8G illustrate step-by-step another exemplary process for forming another all-inorganic wavelength converter according to the present disclosure. Fig. 9 is a flowchart illustrating exemplary operations for forming an all-inorganic wavelength converter according to Fig. 8A-8G illustrates. DETAILED DESCRIPTION

[0009] As used herein, the terms “about” and “substantially,” when used in connection with a numerical value or range, mean + / -5% of the recited numerical value or range.

[0010] Occasionally, one or more aspects of the present disclosure may be described using a numerical range. Unless otherwise stated herein, any recited range should be construed to include iterative values between stated endpoints, as if such iterative values were expressly recited. Such ranges should also be construed to include any and all ranges that fall within or between such iterative values and / or stated endpoints, as if such ranges were expressly recited herein.

[0011] For the purposes of this disclosure, the term “primary light” refers to light emitted by a light emitting diode in a light source.

[0012] The term “secondary light” as used herein means light produced by photoluminescence conversion of primary light by at least one first wavelength conversion material.

[0013] The term "tertiary light" is intended herein to mean light generated by photoluminescence conversion of primary and / or secondary light by at least one second wavelength conversion material. In some embodiments, the second wavelength conversion material is located behind the first wavelength conversion material (e.g., as part of a layer distal from a source of primary light). Alternatively or additionally, the second wavelength conversion material may be homogeneously or heterogeneously mixed with (or otherwise distributed within) the first wavelength conversion material, or a combination thereof. (Higher-order conversion material such as quaternary wavelength conversion material may be defined similarly.) Secondary wavelength conversion material may be a combination of two different red-emitting materials or red / orange-emitting materials.

[0014] The term "output light" is used herein to mean light emitted from a lamp referred to as a light source, that is, light emitted from a lamp in a region distal to a wavelength converter. Output light may include primary light, secondary light, tertiary light, combinations thereof, and the like. Without limitation, output light according to the present disclosure preferably has a color temperature in the range of about 2000 K to about 4500 K, such as about 3000 K. Of course, output light having other color temperatures may be used and is contemplated by the present disclosure.

[0015] References to the color of a phosphor, LED, or conversion material generally refer to its emission color unless otherwise stated. Thus, a blue LED emits blue light, a yellow phosphor emits yellow light, etc.

[0016] One aspect of the present disclosure relates to wavelength converters for solid-state light sources. Generally, the wavelength converters of the present disclosure include at least one first conversion material for converting primary light emitted by a solid-state light source into secondary light. Furthermore, the wavelength converters described herein include at least one second conversion material for converting at least a portion of unconverted primary light and / or secondary light from the first conversion material into tertiary light.

[0017] As may be appreciated, tertiary light produced by a second phosphor material will (by definition) have different spectral characteristics than secondary light produced by a first phosphor material. Thus, the color temperature of the output light from a lamp can be adjusted by controlling the type or characteristic and relative concentration of the first and / or second phosphor. For example, if the characteristics of a first phosphor material are held constant, control of the correlated color temperature of the output light from a lamp can be achieved by adjusting the type, characteristic, and / or concentration of the second conversion material.Although any type of wavelength converter may be used according to the present disclosure, in non-limiting preferred embodiments, the wavelength converters described herein are in the form of a wavelength-converting plate containing one or more layers (e.g., thin films) of conversion material. For clarity, a wavelength converter of this type is referred to herein as a "thin-film converter." In some embodiments, wavelength converters of the present disclosure are in the form of a thin-film converter containing one or more layers of at least a first wavelength conversion material and one or more layers of at least a second wavelength conversion material.

[0018] It will now be Fig. 1A and Fig. 1B, which schematically illustrate the structure of two exemplary lamp configurations according to the present disclosure. In Fig. 1A, an LED light source 100 includes an LED 102 located on an unlabeled upper surface of a carrier 101. The LED light source 100 further includes a wavelength converter 103, which in this case is located on an unlabeled light-emitting surface of the LED 102. For simplicity and ease of understanding, the converter 103 is shown in Fig. 1A and Fig. 1B as a single structure. However, as discussed later, the converter 103 includes multiple layers (e.g., thin films) of different materials, including at least one layer of a first conversion material, a conductive layer, and at least one layer of a second conversion material. Because the converter 103 abuts a surface of the LED 102, it can be understood that the LED light source 100 in Fig. 1A has a CLC structure (Chip Level Conversion).

[0019] How to continue in Fig. 1A, at least a portion of the primary light 104 emitted by the LED 102 may impinge on and be absorbed by the converter 103. The absorption of primary light 104 may excite first and / or second conversion materials within the converter 103 to a higher energy state. When such conversion materials relax to a lower energy state, they may emit unlabeled secondary and / or tertiary light. Output light 105 distal from (i.e., behind) the converter 103 may be emitted by the LED light source 100 and may include a combination of secondary and tertiary light. If not all of the primary light 104 is converted by the converter 103, the output light 105 may also include unconverted primary light.The ratio of primary, secondary and tertiary light in the output light 105 can be determined by the effective conversion efficiency of the conversion materials forming the converter 103.

[0020] Fig. 1B contains the same elements as Fig. 1A, and thus the nature and function of such elements are not repeated. In contrast to Fig. 1A however, the converter 103 is in Fig. 1B is placed at a certain distance away from a light-emitting surface of the LED 102. Because the converter 103 is "spaced" from the LED 102, Fig. 1B can be understood to represent an LED light source with a “removed phosphor” configuration.

[0021] In the interest of clarity and to facilitate understanding, the Fig. 1A and Fig. 1B illustrates the structure of the LED light source 100 in simplified form. It should be understood that the LED light source 100 may include any number of other components that may be included in a lamp. Such components may include, for example, drive electronics, reflectors, a housing, one or more heat sinks, one or more diffusers, combinations thereof, and the like.

[0022] The LED 102 is in Fig. 1A and Fig. 1B as a single structure for clarity. While this configuration is useful, it should be understood that the LED 102 may include multiple LEDs arranged in a pattern or array. Such structures are referred to herein as an "LED core." The number and distribution of LEDs in an LED core can vary widely. For example, the LED cores described herein may include more than 1 to about 100 LEDs or more. In some embodiments, the LED cores include from about 2 to about 75 LEDs, about 3 to about 50 LEDs, about 4 to about 30 LEDs, about 5 to about 25 LEDs, or even about 10 to about 20 LEDs. Of course, LED cores having any number of LEDs are contemplated by the present disclosure and may be used in accordance with the light sources described herein.

[0023] The LED 102 (or a corresponding LED core) may be any known LED, including, but not limited to, a III-V nitride LED such as an InGaN LED. The LED 102 is a source of primary light. In some embodiments, the LED 102 is an LED core that includes one or more blue LEDs, that is, LEDs that emit primary light in the blue portion of the visible region of the electromagnetic spectrum (e.g., from about 450 to about 500 nm). Of course, LEDs that emit in other regions of the electromagnetic spectrum may also be used. For example, in some embodiments, the LED 102 may be an LED core that includes a combination of blue and red LEDs.

[0024] Taking the above into account, one aspect of the present disclosure relates to thin-film converters containing multiple layers of wavelength conversion materials. In particular, one aspect of the present disclosure relates to thin-film converters containing at least one layer of at least one first wavelength conversion material and at least one layer of at least one second wavelength conversion material. Without limitation, the layers of the first and second wavelength conversion materials are preferably in the form of one or more fully inorganic thin films.

[0025] As described in detail below, the layers of first and second wavelength conversion materials can provide desired primary and / or secondary light conversion characteristics while mitigating or avoiding some or all of the limitations of phosphor powder and / or ceramic phosphor embedded in silicone. In particular, the wavelength conversion materials can be selected and / or deposited to possess wavelength conversion characteristics to enable a light source to produce output light with desired optical properties.

[0026] In some embodiments, exemplary wavelength converters according to the present disclosure may convert primary light having a first spectral characteristic into secondary and tertiary light having a second and third spectral characteristic, respectively, to obtain the generation of output light having a desired fourth spectral characteristic. For example, the first wavelength-converting materials described herein may be configured to convert primary light having a first wavelength distribution (e.g., blue light in the range of about 450 to about 500 nm) into secondary light having a second wavelength distribution (i.e., light in the range of 450-700 nm). Furthermore, the second wavelength-converting materials may be configured to convert primary and / or secondary light into tertiary light having a third wavelength distribution (e.g.,green, orange, amber, yellow, and / or red light in the range of about 600 to about 760 nm). Of course, such wavelength ranges are merely exemplary, and any suitable wavelength ranges may be used. Indeed, as described below, the optical characteristics of the at least one first and second wavelength-converting layer can be adjusted in various ways, such as by controlling their composition, their thickness, the manner in which they are deposited, and combinations thereof.

[0027] The thin-film converters of the present disclosure may optionally include a substrate. If used, the substrate may perform the function of supporting one or more layers of conversion material thereon. In this regard, the substrates described herein may be capable of supporting one or more layers of wavelength-converting and / or other materials on their surface(s). In some embodiments, substrates according to the present disclosure are generally planar and have a first (top) and second (bottom) surface, one of which may each support one or more thin films of a first and / or second wavelength-conversion material.

[0028] Any suitable materials may be used to form the substrates described herein. Non-limiting examples of suitable substrate materials include single crystals or polycrystalline materials formed into a rigid plate structure using known ceramic thin-film deposition or crystal growth techniques. Non-limiting examples of useful single-crystal substrate materials include phosphor ceramics such as YAG:Ce (cerium-doped yttrium aluminum garnet) (100), LuAG:Ce (cerium-doped lutetium aluminum garnet), sapphires such as c-sapphire (0001) and r-sapphire (1102), gallium nitride, aluminum gallium nitride (AlGaN), and indium gallium nitride (InGaN). Non-limiting examples of useful polycrystalline substrate materials include YAG, rare earth doped YAG, rare earth doped LuAG, nitride phosphor ceramics such as M2Si5N8:Eu 2+, where M=Ca, Sr, Ba, oxynitride phosphor ceramics such as MSi2O2N2:Eu 2+ , where M=Ca, Sr, Ba, transparent alumina (Al2O3), phosphor ceramics, aluminum nitride (AlN), yttria-stabilized zirconia (YSZ), zirconium oxides, gallium nitride, aluminum gallium nitride (AlGaN), and indium gallium nitride (InGaN). Of course, such materials are only exemplary, and the substrates described herein may be formed on other monocrystalline or polycrystalline materials (e.g., GaN, quartz, silicate phosphor ceramics, etc.), as known to those skilled in the art.

[0029] As previously noted, the wavelength converters described herein need not include a substrate such as those described above. Indeed, in some embodiments, the surface of a light-emitting diode may serve as a substrate for the wavelength conversion layers described herein. Alternatively or additionally, one or more layers of a first and / or second wavelength conversion material may be used as a substrate upon which other conversion layers and / or conductive layers may be deposited. Without limitation, in some embodiments, one or more layers of first wavelength conversion materials are preferably used as a substrate for the subsequent deposition of additional layers of first wavelength conversion materials, conductive material, and / or second wavelength conversion materials.

[0030] In some embodiments, the thin-film wavelength converters of the present disclosure include a substrate capable of withstanding high temperatures that may be used during the deposition and / or post-processing of one or more layers of first and / or second wavelength conversion materials. For example, in some embodiments, the substrates described herein may be capable of withstanding temperatures greater than or equal to 400°C, 600°C, 800°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, 1900°C, or even 2000°C, to which it may be exposed during the deposition and / or post-processing of one or more layers of wavelength conversion material.Such high temperature resistance may be desirable in cases where one or more of the thin films deposited on the substrate may be exposed to high temperatures after processing, such as high-temperature annealing. Sapphire and quartz are non-limiting examples of suitable high-temperature substrate materials, although other materials with high temperature resistance may also be used.

[0031] In further embodiments, the substrates of the present disclosure may correlate to one or more portions of a lamp and / or a solid-state light source such as an LED. For example, the substrates of the present disclosure may be in the form of an LED, as may be useful in chip-level conversion configurations. Alternatively or additionally, the substrates of the present disclosure may be in the form of a carrier coupled to a body (e.g., a reflector body) of a lamp, such that all or part of a wavelength-converting structure formed thereon may be positioned over a solid-state light source, as may be useful in a remote conversion configuration.

[0032] The substrates of the present disclosure may be at least partially transparent to incident primary, secondary, and / or tertiary light. For example, the substrates described herein may be configured to transmit greater than or equal to about 50% of the incident primary, secondary, and / or tertiary light. In some embodiments, the substrates described herein may transmit more than 50% to about 100%, such as greater than or equal to about 60% to about 100%, greater than or equal to about 70% to about 100%, greater than or equal to about 80% to about 100%, greater than or equal to about 90% to about 100%, or even greater than or equal to about 95% to about 100% of the incident primary, secondary, and / or tertiary light. Without limitation, the substrates of the present disclosure preferably exhibit such transmission characteristics for each of the incident primary, secondary, and tertiary light.

[0033] As previously noted, the thin-film wavelength converters of the present disclosure may include one or more layers of at least one first wavelength conversion material. In general, the layer or layers of at least one first wavelength conversion material may function to convert all or a portion of the primary light from a solid-state light source into secondary light. For example, in some embodiments, the layer or layers of at least one first wavelength conversion material may be configured to convert primary light in a first wavelength range (e.g., from about 380 to about 500 nm) into secondary light in a second wavelength range (e.g., from about 380 to about 800 nm).

[0034] In this regard, any suitable conversion material or combination of conversion materials may be used to form the one or more layers of at least one first conversion material. Exemplary materials suitable for use as first wavelength conversion materials include, but are not limited to, phosphors such as oxide garnet phosphors or oxynitride phosphors. In some embodiments, the first conversion material contains or is formed from one or more phosphors selected from: garnets such as Y3Al5O 12 : Ce 3+ , Lu3Al5O 12 :Ce 3+ , Tb3Al5O 12 :Ce 3+ ; Nitrides such as M2Si5N8:Eu 2+ , where M=Ca, Sr, Ba; oxynitrides such as MSi2O2N2:Eu 2+ , where M=Ca, Sr, Ba; silicates such as BaMgSi4O 10 :Eu 2+ , M2SiO4:Eu 2+, where M=Ca, Ba, Sr; combinations thereof, and the like. Alternatively or additionally, the one or more layers of at least one first conversion material may also contain or be formed from one or more of the following materials: MAlSiN3:Eu, where M is a metal selected from Ca, Sr, Ba; A2O3:RE 3+ , where A is selected from Sc, Y, La, Gd, Lu and RE 3+ a trivalent rare earth ion such as Eu 3+ ; and other tertiary and higher metal oxides doped with divalent or trivalent rare earth ions such as Eu 3+ , Ce 3+ , Eu 2+ , Tb 3+etc., including functional groups such as molybdates, niobates, or tungstates. Of course, other conversion materials known to those skilled in the art may also be used to form the one or more layers of at least one first conversion material. Without limitation, the thin-film converters of the present disclosure preferably contain at least one layer of Y3Al5O 12 :Ce 3+ as a first conversion material.

[0035] Thickness is a factor that can influence the amount of primary light that can be converted into secondary light by the layer or layers of first conversion material. Accordingly, the layer or layers of first conversion material can have a thickness selected to achieve a desired degree of primary-to-secondary light conversion. In some embodiments, the thickness is in the range of about 10 nanometers (nm) to about 20 micrometers (µm), such as about 50 nm to about 20 µm, about 500 nm to about 20 µm, or even about 1 µm to about 5 µm.

[0036] The particle size of the phosphor(s) in the one or more layers of at least one first wavelength conversion material may also affect the optical properties of such layers. For example, the particle size of phosphors in the one or more layers of at least one first wavelength conversion material may affect the degree to which such layers scatter incident primary, secondary, and / or tertiary light. Without limitation, the phosphors of the one of more layers of at least one wavelength conversion material may be deposited such that such layers do not significantly scatter primary, secondary, and / or tertiary light. That is, such phosphors may be deposited such that the one or more layers of first conversion material contain less than or equal to about 5% (e.g.≤ 2.5%, ≤ 1%, ≤ 0.5%, or even 0%) of the incident primary, secondary, and / or tertiary light. In other words, the phosphors of the one or more layers can be deposited such that they have a particle size that does not significantly impede the forward propagation of primary light, secondary light, or a combination thereof into a subsequent layer of conversion material.

[0037] Accordingly, the phosphor(s) in the layer(s) of first conversion material in the thin-film converters of the present disclosure may have a particle size distribution selected to achieve desired optical properties, such as, among others, a desired degree of scattering. In some embodiments, the phosphor(s) included in the layer(s) of first conversion material have a particle size distribution in a range from about 100 nm to about 8 µm, such as about 100 nm to about 1 µm, about 100 nm to about 700 nm, about 100 nm to about 500 nm, or even about 100 to about 450 nm. Without limitation, the particle size of the phosphor(s) of the layer(s) of first conversion material is preferably less than or equal to the wavelength of the incident primary light, e.g., to reduce the scattering of incident primary light.If the incident primary light is in a wavelength range of about 450 to about 500 nm, the particle size of the phosphor(s) of the layer(s) of first conversion material is preferably less than or equal to about 450 nm, such as about 100 to about 400 nm.

[0038] The layer or layers of at least one first conversion material may be deposited or otherwise formed on a substrate or other support in any suitable manner. For example, the layer or layers of at least one first conversion material may be deposited using a first deposition process, such as, but not limited to, physical vapor deposition, chemical vapor deposition, sputtering, pulsed laser deposition, electrophoretic deposition, or any other deposition technique. Without limitation, the one or more layers of at least one first conversion material are formed by pulsed laser deposition (PLD). As will be understood, PLD may be capable of depositing thin films of highly stoichiometric materials with a complex phosphor composition, each layer having a controlled thickness, e.g.of about 20 µm or any other desired thickness. Of course, deposition of the first conversion material by PLD is not required. Indeed, in other preferred embodiments, the layer or layers of first conversion materials may be deposited using electrophoretic deposition, e.g., on a luminescent substrate or other substrate.

[0039] After deposition, the layer or layers of at least one first conversion material may be subjected to post-processing, including, but not limited to, thermal post-processing such as annealing. For example, the layer or layers of at least one first conversion material may be annealed, e.g., to encourage grain growth or for other purposes. Without limitation, the layer or layers of first conversion material are preferably annealed after deposition at a temperature in the range of about 400°C to about 2000°C, such as about 600°C to about 2000°C, about 800°C to about 2000°C, about 1000°C to about 1900°C, about 1200°C to about 1800°C, or even about 1400°C to about 1700°C. In some embodiments, the layer or layers of first conversion materials are annealed at about 1600°C. Annealing can be carried out in air or in another environment such as an inert gas environment (e.g.Helium, neon and argon) in a vacuum, in an oxygen environment, in a nitrogen environment or in a forming gas environment (e.g. 1-10% hydrogen, balance nitrogen).

[0040] In some embodiments, the layer or layers of at least one first conversion material can be processed after deposition into a pattern or other structure. For example, the layer or layers of at least one first conversion material can be processed into a plurality of phosphor "islands" that are in contact with a surface of a substrate or one or more sublayers on the surface of a substrate. In this way, a layer of first conversion material can be processed into "pixels" (e.g., three-dimensional islands with a height, a width, and a gap distance), upon which other layers / materials can be deposited. Such processing can be performed, for example, by subjecting a deposited layer of at least one first conversion material to an etching process, such as, but not limited to, photolithography.

[0041] In cases where photochemical etching is used, a photoresist mask may be deposited (e.g., by spin coating) on a first layer of at least one first conversion material. The photoresist mask may be fully or partially exposed to light to form an exposed structure within the mask. Depending on the mask, the exposed or unexposed portions of the photoresist may then be removed using a developing solution known in the art, thereby exposing portions of the layer of first wavelength conversion material(s) while others remain protected by the photoresist mask. The resulting structure may then be exposed to a wet or dry etchant, which may remove portions of the first wavelength conversion material(s) in areas not protected by the photoresist mask. The photoresist mask may then (e.g.,with a solvent) or retained, after which the structure can be further processed as discussed below.

[0042] The thin-film wavelength converters of the present disclosure may also include one or more layers of at least one second wavelength conversion material. As previously noted, the layer or layers of at least one second wavelength conversion material may function to convert all or part of the incident primary (e.g., unconverted primary light from a solid-state light source) and / or secondary light emitted by the layer or layers of at least one first wavelength conversion material into tertiary light. The tertiary light may include light in a different wavelength range than the primary and secondary light. Alternatively or additionally, the tertiary light may include light in a wavelength range encompassed by the second wavelength range of the secondary light, but with a different (e.g.,higher) concentration than the secondary light generated by the layer or layers of first wavelength conversion material.

[0043] For example, the layer or layers of the first wavelength conversion material(s) may convert all or part of the incident primary light into output light. Although the output light may include light in various portions of the visible region of the electromagnetic spectrum, the intensity of light may be relatively lower at certain portions of that region than at others. For example, the output light may include relatively large amounts of light in the blue portion of the visible region, but relatively small amounts of light in the green, orange, yellow, and / or red portions of the visible region. As a result, the color temperature of the output light may be relatively cool, e.g., in a range of about 5000 K to about 10,000 K.

[0044] In such cases, the layer or layers of the second wavelength conversion material(s) can generate tertiary light with a relatively high light intensity in the green, orange, yellow, and / or red portion of the visible range. In particular, they can be configured to generate additional light in the red portion of the electromagnetic spectrum to "warm up" the output light from a lamp. Non-limiting examples of such materials include yellow-green phosphors such as cerium-doped garnets, such as Lu3Al5O. 12 :Ce 3+ and Tb3Al5O 12 :Ce 3+ etc.; red / amber nitrides such as M2Si5N8:Eu 2+ , where M=Ca, Sr, Ba; red / amber oxynitrides such as MSi2O2N2:Eu 2+ , where M=Ca, Sr, Ba; and red / yellow / green emitting silicates such as BaMgSi4O 10 :Eu 2+ and M2SiO4:Eu 2+, where M=Ca, Ba, Sr. Without limitation, the materials used to form the layer or layers of the second wavelength conversion material(s) are preferably different from the materials used to form the layer or layers of the first wavelength conversion material(s). Without limitation, the layer or layers of the second wavelength conversion material(s) preferably contain or are formed from a europium-activated strontium silicon nitride or a strontium silicon oxynitride phosphor, such as those identified above.

[0045] In some embodiments, the layer or layers of second wavelength conversion materials may be configured to generate tertiary light having a color temperature in the range of about 2000 K to about 3500 K, such as about 2700 K to about 3200 K. In some embodiments, the tertiary light generated by the layer or layers of at least one second wavelength conversion material is configured such that the output light behind the converter has a color temperature in the range of about 2500 K to about 4000 K, such as about 3000 K to about 3500 K, or even about 3000 K.

[0046] Like the layer or layers of first wavelength conversion materials, the thickness of the layer or layers of at least one second wavelength conversion material can affect the optical performance. For example, the thickness of the layer or layers of the second wavelength conversion material can affect the degree to which such layer or layers can convert primary and / or secondary light into tertiary light. Accordingly, the thickness of the layer or layers of second wavelength conversion materials can be selected to achieve the desired optical properties.In some embodiments, the thickness of the layer or layers of second wavelength conversion materials may range from about 10 nanometers (nm) to about 20 micrometers (µm), such as about 50 nm to about 20 µm, such as about 500 nm to about 20 µm, or even such as about 1 µm to about 5 µm.

[0047] The particle size of one or more phosphors in the layer(s) of at least one second wavelength conversion material may also affect the optical properties of one or more such layers. For example, the particle size of the phosphor(s) in the layer(s) of at least one second wavelength conversion material may affect the degree to which such layer(s) scatter incident primary and / or secondary light. Without limitation, the phosphors of the layer(s) of at least one second wavelength conversion material may be deposited such that such layers do not substantially scatter incident primary or secondary light. That is, the layer(s) of at least one second wavelength conversion material may be deposited such that they scatter less than or equal to about 5% of the incident primary and / or secondary light.In other words, the layer or layers of second conversion material can be deposited in such a way that they do not substantially impede the forward transmission of incident primary and / or secondary light into a subsequent conversion layer.

[0048] Accordingly, the phosphor(s) in the layer(s) of second wavelength conversion material(s) may have a particle size selected to achieve desired optical properties, such as, among other things, a desired degree of scattering. In some embodiments, the phosphor(s) contained in the layer(s) of second wavelength conversion material(s) have a particle size in the range of about 100 nm to about 8 µm, such as about 100 nm to about 1 µm, about 100 nm to about 700 nm, about 100 nm to about 500 nm, or even about 100 to about 400 nm. Without limitation, the particle size of the phosphor(s) of the layer(s) of second wavelength conversion material(s) is less than or equal to the wavelength of incident primary and / or secondary light.If the incident primary light is in a wavelength range from about 450 nm to about 500 nm, the particle size of the phosphor(s) of the layer(s) of the second wavelength conversion material(s) is preferably less than or equal to about 450 nm, such as about 100 to about 400 nm.

[0049] The layer or layers of second wavelength conversion material may be deposited or otherwise formed on a substrate or other support (e.g., on or over a layer of first wavelength conversion material) in any suitable manner. For example, the layer or layers of the second wavelength conversion material may be deposited using physical vapor deposition, chemical vapor deposition, sputtering, pulsed laser deposition, electrophoretic deposition, or any other deposition technique.

[0050] As will be understood, at least one second wavelength conversion material may include or be present in the form of a green, yellow, or red phosphor having a relatively complex stoichiometry. Due to this stoichiometric complexity, it may be difficult to deposit such phosphors using techniques such as physical vapor deposition, sputtering, and pulsed laser deposition. For example, in the case of sputtering, it may be difficult to obtain suitable sputtering targets from which to deposit a layer of second wavelength conversion material. The physical vapor deposition of the second wavelength conversion material(s) can also be complex, requiring careful control of numerous feed gases to obtain layers with a desired chemistry.Thus, without limitation, the layer or layers of second wavelength conversion material are preferably deposited using electrophoretic deposition.

[0051] For example, in cases where nitride phosphors are used as the second wavelength conversion material, electrophoretic deposition of such phosphors may occur by introducing nitride phosphor particles into a bath containing a solvent (e.g., isopropyl alcohol or another suitable solvent) containing dissolved nitrate salts and water. The nitrate salts may dissociate to some extent in the solvent, thereby yielding ions that can positively or negatively charge the phosphor particles. The deposition of phosphor particles may proceed by immersing an electrode and a workpiece (e.g., a substrate with one or more layers of a first wavelength conversion material thereon) in the bath and applying a voltage to electrically bias the workpiece relative to the electrode.For example, if the phosphor particles are positively charged, deposition can be achieved by negatively precharging the workpiece and positively precharging the electrode, thereby driving the positively charged phosphor towards the negatively biased workpiece.

[0052] To facilitate the electrophoretic deposition of the layer or layers of the second wavelength conversion material(s), one or more conductive layers may be used. In use, the conductive layer or layers may be deposited on all or part of the workpiece (at this point, a portion of a thin-film converter). For example, where one or more layers of one or more first wavelength conversion materials have been deposited on a first side of a planar substrate, a conductive layer may be deposited on the layer or layers of the first wavelength conversion material(s), on a second side of the planar substrate, or a combination thereof.As will be understood, the conductive layer may facilitate the electrical biasing of the workpiece and thus the electrophoretic deposition of the layer or layers of the second wavelength conversion material(s).

[0053] Any suitable conductive material may be used to form conductive layers according to the present disclosure. Examples of such materials include, but are not limited to, metals (e.g., gold, copper, aluminum, etc.), indium tin oxide (ITO), aluminum-doped zinc oxide (ZnO:Al), gallium-doped zinc oxide, niobium-doped strontium titanium oxide (SrTiO3:Nb), indium gallium zinc oxide (IGZO), doped tin oxide, graphene, lead zirconate titanate (PZT), combinations thereof, and the like. Without limitation, the conductive layers of the present disclosure are preferably transparent and formed from indium tin oxide.

[0054] The conductive layers of the present disclosure are preferably configured to transmit desired amounts of primary, secondary, and tertiary light. For example, the conductive layers may be configured to transmit greater than or equal to about 50%, such as greater than or equal to about 60%, 70%, 80%, 90%, 95%, 99%, or even 100% of the primary, secondary, and tertiary light.

[0055] After deposition, the layer or layers of the second wavelength conversion material(s) may be subjected to post-processing, including, but not limited to, thermal post-processing such as annealing. The processing parameters suitable for use in the thermal post-processing of the layer or layers of the second wavelength conversion material(s) are the same as those specified above for the layer or layers of the first wavelength conversion material(s) and are not repeated for brevity.

[0056] In some embodiments, the layer or layers of the second wavelength conversion material may be deposited directly on the surface of a layer of first wavelength conversion material or directly on a surface of a conductive layer present on a surface of a layer of first wavelength conversion material. Accordingly, the thin-film wavelength converters may have a layer structure S:A:B or S:A:C:B, where S corresponds to a substrate, A corresponds to one or more layers of a first wavelength conversion material, B corresponds to one or more layers of a second wavelength conversion material, and C corresponds to one or more layers of a conductive material. Alternatively or additionally, the thin-film wavelength converters may have a layer structure A:S:B or A:S:C:B, where A, B, C, and S are as defined above.In any case, the layers can be repeated one or more times on one or both sides of the substrate. Thus, the thin-film wavelength converters described above can, for example, have a layer structure S:A:B:A:B:A:B...S:A:C:B:A:C:B...A:S:C:B:C:B:C:B, where A, B, C, and S are as defined above.

[0057] In some embodiments, the layer or layers of the second wavelength conversion material(s) may be processed into a pattern or structure after deposition. For example, the layer or layers of the second wavelength conversion material(s) may be processed into a plurality of phosphor "islands" that may be in contact with a surface of a layer of a first wavelength conversion material or a conductive material. In this way, a layer of second conversion material may be processed into "pixels" (e.g., three-dimensional islands having a height, a width, and a gap spacing). Such processing may be performed, for example, by subjecting a deposited layer of a second wavelength conversion material to an etching process, such as, but not limited to, photolithography.The manner in which such processing can be performed is the same as that specified above for the layer or layers of the first wavelength conversion material(s) and thus will not be repeated. By patterning the layer or layers of the second wavelength conversion material(s), it may be possible to control the amount of tertiary light added to the output light of a light source. Consequently, the color temperature of the output light can be controlled by appropriately etching / patterning the layer or layers of the second wavelength conversion material(s).

[0058] For illustrative purposes, the present disclosure will now proceed to describe exemplary thin-film wavelength converters according to the present disclosure, as well as exemplary methods of fabricating them. It should be understood that such examples are for illustrative purposes only, and that other thin-film converter configurations and fabrication methods may be used and are contemplated by the present disclosure.

[0059] In view of the above, we now turn to the Fig. 2A-2D, which sequentially illustrate the formation of an example of a thin-film converter according to the present disclosure. The sequential illustration in Fig. 2A-2D generally agree with the various Fig. 3, which is a flowchart illustrating operations performed according to an exemplary method for forming a thin-film converter according to the present disclosure. Accordingly, where possible, the operations performed in Fig. 3 outlined operations in connection with the sequential representation of Fig. 2A-2D.

[0060] As in Fig. 2A-D, the production of a thin-film converter 103' according to the present disclosure may begin with the provision of a substrate 201. As shown, the substrate 201 may be generally planar and include a top and bottom surface (not labeled), one of which may support one or more thin films of wavelength conversion material. For the sake of illustration, Fig. 2A-D sequentially illustrate the production of a thin-film converter 103' including two layers of wavelength conversion material on its upper (first) surface. However, it should be understood that any number of layers of conversion material may be used, and that such conversion layers may be present on either or both of the upper and lower surfaces of the substrate 201.

[0061] Substrate 201 may be formed from any material that provides a stable structure upon which one or more layers 202 of at least one first wavelength conversion material can be deposited. Suitable materials include those previously described. Without limitation, substrate 201 is preferably a sapphire substrate, which may be planar or non-planar.

[0062] After the substrate 201 has been provided or otherwise made available, the production of the thin film converter (e.g., according to box 302 of Fig. 3) by depositing a layer of a first wavelength conversion material 202 on an upper (first) surface of the substrate 201. Suitable materials for forming the first wavelength conversion material 202 include those previously identified as suitable first wavelength conversion materials. Without limitation, the first wavelength conversion material 202 is preferably made of Y3Al5O 12 :Ce 3+ trained. While the Fig. 2A-2D depict a first wavelength conversion material 202 as a conformal coating, such a structure is not required. Indeed, as previously noted, the first layer of first wavelength conversion material 202 may be deposited or processed into islands or pixels of first wavelength conversion material, e.g., using photochemical etching and / or a selective deposition process.

[0063] The deposition of the first wavelength conversion material 202 may be performed using any suitable deposition process, such as those previously described as suitable for depositing first wavelength conversion materials. Without limitation, the first wavelength conversion material is preferably deposited on the substrate 201 using pulsed laser deposition (PLD) or electrophoretic deposition.

[0064] In some embodiments, the first wavelength conversion material 202 may be subjected to one or more post-processing processes (e.g., according to optional block 303 of Fig. 3). For example, the first wavelength conversion material may be subjected to a heat treatment, e.g., for grain growth or for other purposes. In some embodiments, the substrate 201 and the first wavelength conversion material 202 are subjected to a heat treatment at approximately 1400 to 1600°C.

[0065] After the first wavelength conversion material 202 has been deposited and optionally post-processed, the production of the thin film converter (e.g., according to block 304 of Fig. 3) by depositing the conductive layer 203 on the exposed surface of the first wavelength conversion material 202, as in Fig. 2C. The conductive layer 203 may be formed from any suitable conductive material, as previously described. Without limitation, the conductive layer 203 is formed from indium tin oxide, graphene, or a combination thereof. In cases where the first wavelength conversion material 202 is deposited as a conformal coating, the conductive layer 203 may also be deposited as a conformal coating, as shown in Fig. 2C. Alternatively or additionally, the conductive layer 203 may be selectively deposited or processed into islands of conductive material, as described later in connection with another embodiment of the present disclosure.

[0066] Any suitable process may be used to deposit the conductive layer 203 on the first wavelength conversion material 202. Without limitation, the conductive layer 203 is preferably deposited on the conversion material 202 using sputtering or another physical deposition technique.

[0067] After the conductive layer 203 has been deposited, the production of the thin film converter (e.g., according to block 305 of Fig. 3) by depositing the second wavelength conversion material 204 on the exposed (e.g., top) surface of the conductive layer 203. The second wavelength conversion material 204 may be formed from any suitable wavelength conversion material and preferably includes or is formed from different wavelength conversion materials than the first wavelength conversion material 202. Suitable materials for forming the second wavelength conversion material 204 include those previously described. Without limitation, the second wavelength conversion material 204 is preferably formed from a europium-activated strontium nitride or oxynitride phosphor.

[0068] Any suitable deposition technique may be used to deposit the second wavelength conversion material 204, as previously noted. Without limitation, the second wavelength conversion material 204 is preferably deposited using electrophoretic deposition. Such deposition may be performed, for example, by immersing the Fig. 2C into a bath containing a solvent, one or more salts, and charged particles of the second wavelength conversion material, as generally described above.

[0069] After the second wavelength conversion material 204 has been deposited, it may (according to optional block 306 of Fig. 3) be subjected to post-processing, e.g. heat treatment, tempering, subsequent coating processes, etc. After such post-processing is completed (or if no post-processing is carried out), the method can be continued according to block 307 of Fig. 3 ends.

[0070] It will now be Fig. 4A-4G, which sequentially illustrate the formation of another exemplary thin-film converter according to the present disclosure. The sequential representation in Fig. 4A-4G generally agrees with the Fig. 5, which is a flowchart illustrating operations performed according to an exemplary method for forming a thin-film converter according to the present disclosure. Accordingly, where possible, the Fig. 5 outlined operations in connection with the sequential representation of Fig. 4A-4G described.

[0071] As in Fig. 4A-4C and blocks 501-504 of Fig. 5, the production of a thin-film converter 103'' according to the present disclosure may begin with the provision of a substrate 201, the deposition of a first wavelength conversion material 202, and the deposition of the conductive layer 203. The nature of these layers and the manner in which they are formed is the same as described above in connection with the elements 201-203 and the blocks 301-304 of the Fig. 2A-2D and 3. Thus, for the sake of brevity, the nature and production of such elements will not be repeated.

[0072] Now with reference to the Fig. 4D-4E and Block 505 of Fig. 5, the production of the thin-film converter 103'' may proceed by depositing a layer of photoresist 401, e.g., via dip coating, spraying, or another suitable deposition technique. After the photoresist 401 has been deposited, it may be processed to form a patterned photoresist 401', e.g., using photochemical etching, photolithography, or other methods known in the art. As shown in Fig. 4E, the patterned photoresist 401' forms a mask that may include islands of photoresist that protect underlying portions of the conductive layer 203 while leaving other portions of the conductive layer 203 exposed.

[0073] At this point, the production of the thin film converter 103'' (according to block 506 of Fig. 5) by depositing the second wavelength conversion material 204 on the exposed portions of the conductive layer 203, as in Fig. 4F. According to the description of the Fig. 2D and Fig. 3, the deposition of the second wavelength conversion material 204 may be performed in any suitable manner. Without limitation, electrophoretic deposition is preferably used to deposit the second wavelength conversion material 204 on the exposed portions of the conductive layer 203.

[0074] After the second wavelength conversion material 204 has been deposited on the exposed portions of the conductive layer 203, the production of the thin film converter 103'' may optionally (e.g., according to optional block 507 of Fig. 5) by removing the patterned photoresist 401', leaving islands of second wavelength conversion material 204 on the conductive layer 203, as in Fig. 4G. Before or after removing the patterned photoresist 401', the second wavelength conversion material 204 may be subjected to post-processing, such as heat treatment, annealing, etc., as generally described above. At block 509, the method ends.

[0075] It will now be Fig. 6A-6D, which sequentially illustrate the formation of another exemplary thin-film converter according to the present disclosure. The sequential representation in Fig. 6A-6D generally agree with the Fig. 7, which is a flowchart illustrating operations performed according to an exemplary method for forming a thin-film converter according to the present disclosure. Accordingly, where possible, the Fig. 7 outlined operations in connection with the sequential representation of Fig. 6A-6D.

[0076] As in Fig. 6A and blocks 701-703 of Fig. 7, the production of a thin-film converter 103''' according to the present disclosure may begin with the provision of a substrate 201 and the deposition of the first wavelength conversion material 202. These operations are generally the same as those described above in connection with elements 201-202 and blocks 301-303 of the Fig. 2A, Fig. 2B and Fig. 3, except that the first wavelength conversion material 202 is deposited on a second (bottom) surface of the substrate 201 instead of a first (top) surface of the substrate 201. Thus, for brevity, the nature and production of such elements will not be repeated in detail. In some embodiments, pulsed laser deposition or electrophoretic deposition may be used to form the first wavelength conversion material 202 on the second (bottom) surface of the substrate 201. Referring now to Fig. 6C and Block 704 of Fig. 7, the production of the thin-film converter 103''' may proceed by depositing the conductive layer 203 on a first (top) surface of the substrate 201. The nature and deposition of the conductive layer 203 is the same as previously described in connection with previous embodiments, except that it is formed on a surface of the substrate 201 opposite the surface on which the first wavelength conversion material 202 was deposited. Accordingly, the nature and production of the conductive layer 203 is not repeated.

[0077] As in Fig. 6D and according to blocks 705 and 706 of Fig. 7, the production of the thin-film converter 103''' may proceed by depositing the second wavelength conversion material 204 on the exposed surface of the conductive layer 203. According to previous descriptions, the deposition of the second wavelength conversion material 204 may be performed in any suitable manner. Without limitation, electrophoretic deposition is preferably used to deposit the second wavelength conversion material 204 on the exposed portions of the conductive layer 203. The deposited second conversion material 204 may optionally be post-processed (e.g., according to block 706 of Fig. 7). The procedure ends at block 707.

[0078] It will now be Fig. 8A-8G, which sequentially illustrate the formation of another exemplary thin-film converter according to the present disclosure. The sequential representation in Fig. 8A-8G generally agrees with the Fig. 9, which is a flowchart illustrating operations performed according to an exemplary method for forming a thin-film converter according to the present disclosure. Accordingly, where possible, the Fig. 9 outlined operations in connection with the sequential representation of Fig. 8A-8G described.

[0079] As in Fig. 8A-8C and blocks 901-904 of Fig. 9, the production of a thin-film converter 103'''' according to the present disclosure may begin with the provision of a substrate 201, the deposition of a first wavelength conversion material 202 on a second (bottom) surface of the substrate 201, and the deposition of the conductive layer 203 on a first (top) surface of the substrate 101. The nature of these layers and the manner in which they are formed is the same as described above in connection with elements 201-203 and blocks 701-704 of the Fig. 6A-6C and 7. Thus, for the sake of brevity, the nature and production of such elements will not be repeated.

[0080] Now with reference to the Fig. 8D-8E and Block 905 of Fig. 9, the production of the thin-film converter 103'''' may proceed by depositing a layer of photoresist 401, e.g., via dip coating, spraying, or another suitable deposition technique. After the photoresist 401 has been deposited, it may be processed to form a patterned photoresist 401', e.g., using photochemical etching, photolithography, or other methods known in the art. As shown in Fig. 8E, the patterned photoresist 401' forms a mask that may include islands of photoresist that protect underlying portions of the conductive layer 203 while leaving other portions of the conductive layer 203 exposed.

[0081] At this point, the production of the thin film converter 103'''' (according to block 906 of Fig. 9) by depositing the second wavelength conversion material 204 on the exposed portions of the conductive layer 203, as in Fig. 8F. According to previous descriptions, the deposition of the second wavelength conversion material 204 may be performed in any suitable manner. Without limitation, electrophoretic deposition is preferably used to deposit the second wavelength conversion material 204 on the exposed portions of the conductive layer 203.

[0082] After the second wavelength conversion material 204 has been deposited on the exposed portions of the conductive layer 203, the production of the thin film converter 103'''' may optionally (e.g., according to optional block 907 of Fig. 9) by removing the patterned photoresist 401', leaving islands of second wavelength conversion material 204 on the conductive layer 203, as in Fig. 8F. Before or after removing the patterned photoresist 401', the second wavelength conversion material 204 may be subjected to post-processing, such as heat treatment, annealing, etc., as generally described above. At block 909, the method ends.

[0083] While the Fig. 2A-9 describe the formation of wavelength converters in which one or more phosphor layers and conductive layers are deposited on a substrate 201, it should be understood that the use of the substrate 201 is not required. In fact, in the embodiments of Fig. 2A-8G, the substrate 201 may be omitted and the first wavelength conversion material 202 may be used as a substrate for the subsequent deposition of the conductive layer or layers, the second wavelength conversion material layer(s) and the photoresist layer or layers (where applicable).

[0084] The following examples describe thin film converters according to the present disclosure and are for illustrative purposes only.

[0085] Example 1 - Deposition of the first wavelength conversion material. YAG:Ce thin films were grown on c-sapphire, r-sapphire, quartz, and phosphor ceramic substrates. The YAG:Ce films were deposited using PLD in an oxygen atmosphere at 3 mTorr. The laser pulse repetition rate was varied from 5 to 50 hertz (Hz). The substrate temperature during deposition varied from room temperature to approximately 1000°C. After deposition, the samples were annealed using a belt furnace at temperatures ranging from 1400–1600°C in an H2N2 atmosphere.

[0086] Example 2 - Deposition of the Conductive Layer. Conductive layers were deposited on the samples prepared according to Example 1. Specifically, RF sputtering was performed using a KJ Lesker 2" sputtering gun to produce thin conductive films of indium tin oxide (ITO) on the samples. Before sputtering, the samples were cleaned in an acetone-isopropanol ultrasonic bath. A 2-inch ITO target (10 wt% SnO2) was used for deposition. The base pressure of the system was 1×10 -7 Torr. ITO sputtering was performed at a pressure of 5–20 mTorr in an argon-oxygen atmosphere. The applied RF power varied from 50–200 W. Sputtering was carried out for approximately 10 minutes at approximately 400°C and resulted in the production of 300 nm thick ITO layers on the samples from Example 1. After deposition, the samples were annealed for approximately 2 hours in an oxygen atmosphere at 400°C.

[0087] Example 3 - Deposition of the second wavelength conversion material. Layers of the second wavelength conversion material (M2Si5N8:Eu 2+ , where M=Ca, Sr, Ba) were deposited on the conductive layers of the samples prepared according to Example 2. In particular, electrophoretic deposition was used to prepare a Sr2Si5N8:Eu 2+-phosphor on the conductive layers of the samples prepared according to Example 2. Electrophoretic deposition was carried out using a suspension bath containing the nitride phosphor particles, isopropyl alcohol, dissolved nitrate salts, and water. The nitrate salts dissociated slightly to provide ions that charged the nitride phosphor particles. An electrode and the samples from Example 2 were immersed in the bath. A voltage of about 10 V to about 800 V was applied to the electrode and the conductive layers of the samples from Example 2 to cause the charged nitride particles to adhere to the surface of the conductive layers. The deposition time varied between 5 seconds and 100 seconds, with the longer time resulting in a greater thickness of up to about 20 µm.

Claims

[1] Thin film wavelength converter comprising: a substrate; a first thin film layer, wherein the first thin film layer comprises at least a first wavelength conversion material; a conductive layer; and a second thin film layer deposited on the conductive layer, the second thin film layer comprising at least a second wavelength conversion material; where: the first thin-film layer is configured to convert incident primary light from a light source in a first wavelength range into secondary light in a second wavelength range; and the second thin film layer is configured to convert at least one of the primary light and the secondary light into tertiary light in a third wavelength range, wherein the second wavelength range is different from the third wavelength range. [2] The thin film wavelength converter of claim 1, wherein the first wavelength conversion material is selected from the group consisting of garnet phosphors, oxynitride phosphors, nitride phosphors, silicate phosphors, and combinations thereof. [3] The thin film wavelength converter of claim 1, wherein the first thin film layer has a thickness in the range of about 10 nanometers (nm) to about 20 micrometers (µm). [4] Thin film wavelength converter according to claim 1, wherein the at least one second wavelength conversion material is selected from Y3Al5O 12 :Ce 3+ , Lu3Al5O 12 :Ce 3+ , Tb3Al5O 12 :Ce 3+ , M2Si5N8: Eu 2+ , MSi2O2N2:Eu 2+ , BaMgSi4O 10 :Eu 2+ , M2SiO4: Eu 2+ , MAlSiN3:Eu 2+ and combinations thereof, wherein M is selected from calcium, barium, strontium and combinations thereof. [5] The thin film wavelength converter of claim 1, wherein the second thin film layer comprises islands of the at least second wavelength conversion material on the conductive layer. [6] The thin film wavelength converter of claim 1, wherein the substrate comprises an upper and lower surface, and the first thin film layer is deposited on the upper surface and the conductive layer is deposited on the first thin film layer. [7] The thin film wavelength converter of claim 1, wherein the substrate comprises an upper and lower surface, and the first thin film layer is deposited on the lower surface and the conductive layer is deposited on the upper surface. [8] The thin-film wavelength converter according to claim 1, wherein the substrate is formed of a material selected from the group consisting of sapphire, at least one phosphor ceramic, polycrystalline transparent alumina, aluminum nitride, yttria-stabilized zirconia (YSZ), zirconium oxides, gallium nitride, aluminum gallium nitride (AlGaN), and indium gallium nitride (InGaN). [9] The thin film wavelength converter according to claim 1, wherein the conductive layer consists of at least one of the following: a metal film, indium tin oxide (ITO), aluminum-doped zinc oxide (ZnO:Al), gallium-doped zinc oxide, niobium-doped strontium titanium oxide (SrTiO3:Nb), indium gallium zinc oxide (IGZO). [10] A method of forming a thin film wavelength converter comprising: Depositing a first thin film layer of at least one first wavelength conversion material on a substrate using a first deposition process; depositing a conductive layer using a second deposition process; and Depositing a second thin film layer of at least one second wavelength conversion material on the conductive layer using an electrophoretic deposition process; where: the first thin-film layer is configured to convert incident primary light from a light source in a first wavelength range into secondary light in a second wavelength range; and the second thin film layer is configured to convert at least one of the primary light and the secondary light into tertiary light in a third wavelength range, wherein the second wavelength range is different from the third wavelength range. [11] The method of claim 10, wherein the first deposition process is selected from the group consisting of physical vapor deposition, electrophoretic deposition, chemical vapor deposition, epitaxy, sputtering, pulsed laser deposition, and combinations thereof. [12] The method of claim 10, wherein the first wavelength conversion material is selected from the group consisting of garnet phosphors, oxynitride phosphors, nitride phosphors, silicate phosphors, and combinations thereof. [13] The method according to claim 10, wherein the at least one second wavelength conversion material is selected from Y3Al5O 12 : Ce 3+ , Lu3Al5O12 : Ce 3+ , Tb3Al5O 12 : Ce 3+ , M2Si5N8:Eu 2+ , MSi2O2N2:Eu 2+ , BaMgSi4O 10 :Eu 2+ , M2SiO4:Eu 2+ , MAlSiN3:Eu 2+ and combinations thereof, wherein M is selected from calcium, barium, strontium and combinations thereof. [14] The method of claim 10, further comprising applying a photoresist mask to the conductive layer prior to depositing the second thin film layer, the photoresist mask having a pattern that exposes portions of the conductive layer. [15] The method of claim 14, wherein the second thin film layer is structured to form islands of the at least second wavelength conversion material on the conductive layer. [16] The method of claim 10, wherein the substrate comprises a top and bottom surface and the first thin film layer is deposited on the top surface and the conductive layer is deposited on the first thin film layer. [17] The method of claim 10, wherein the substrate comprises a top and bottom surface and the first thin film layer is deposited on the bottom surface and the conductive layer is deposited on the top surface.

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