Method for producing structure, structure and optoelectronic component

Abstract

A method for producing a structure is specified. According to one embodiment, the method comprises: providing a nanocrystal configured to convert primary radiation to secondary radiation; and forming an encapsulation surrounding the nanocrystal using the coordination complex, wherein the encapsulation comprises an oxide. In addition, structures and optoelectronic devices are specified.

Description

[0001] Methods for producing structures, structures and optoelectronic devices are described in detail.

[0002] It is an object to provide methods for producing structures with good quantum yield. It is another object to provide structures and optoelectronic devices with improved efficiency.

[0003] Methods for producing structures are described in detail. The structures can comprise different elements, components or parts with specific, in particular different, properties.

[0004] According to one embodiment, the method for producing a structure comprises providing a nanocrystal configured to convert primary radiation into secondary radiation. In other words, the nanocrystal converts electromagnetic radiation of a first wavelength range (primary radiation) into electromagnetic radiation of a second wavelength range (secondary radiation). In particular, the nanocrystal absorbs electromagnetic radiation of the first wavelength range, converts the electromagnetic radiation of the first wavelength range into electromagnetic radiation of the second wavelength range and emits the electromagnetic radiation of the second wavelength range. For example, the second wavelength range is in the visible wavelength range or in the IR wavelength range. For example, the second wavelength range is 500 nm to 2000 nm, including the two end values. In particular, the second wavelength range is 500 nm to 1000 nm, including the two end values.

[0005] In particular, the nanocrystal is a particle having a diameter of 1 nm to 100 nm and including 1 nm and 100 nm, for example 2 nm to 20 nm and including 2 nm and 20 nm. Due to its size, the nanocrystal has different properties than a bulk material formed of the same material. For example, the nanocrystal is spherical, rod-shaped or cuboid. The surface of the nanocrystal can be uniform or non-uniform.

[0006] For example, the nanocrystal comprises or consists of a nanoparticle, a phosphor particle or a quantum dot. A nanoparticle is generally defined as a particle of a substance having a diameter of 1 nanometer to 100 nanometers. The nanoparticle can be silver, silicon dioxide, zinc oxide, titanium dioxide, diamond, copper, cobalt oxide, boron nitride, zirconium dioxide, tungsten, aluminum oxide, boron, palladium, calcium carbonate and calcium sulfonate.

[0007] The phosphor can be a ceramic phosphor. The phosphor can be in the form of a phosphor particle. The phosphor particle preferably comprises a crystal, for example a ceramic, in the main crystal lattice of which a foreign element is introduced as an activator element. For example, the phosphor can be a ceramic material. Preferably, the ceramic phosphor comprises a garnet phosphor. In particular preferably, the garnet phosphor is a YAG phosphor having the chemical formula Y3(Al,Ga)5O12:Ce or a LuAG phosphor having the chemical formula Lu3(Al,Ga)5O12:Ce. 12 :Ce or a LuAG phosphor having the chemical formula Lu3(Al,Ga)5O12:Ce. 12: Ce-doped LUAG phosphors. In addition, the ceramic phosphors can also include nitride and / or oxynitride phosphors. The nitride or oxynitride phosphors can be, for example, an alkaline earth metal silicon oxynitride, an oxynitride, an aluminum oxynitride, a silicon nitride, or a sialon.

[0008] In addition, the nanocrystals comprise or consist of a semiconductor material. The semiconductor material is, for example, a III-V compound semiconductor material, a II-VI compound semiconductor material, or a II-III-V compound semiconductor material. The III-V compound semiconductor material comprises at least one element of group 13 of the periodic table (e.g. B, Al, Ga, In) and at least one element of group 15 of the periodic table (e.g. N, P, As). The II-VI compound semiconductor material comprises at least one element of group 2 or 12 of the periodic table (e.g. Zn, Cd, Mg) and at least one element of group 16 of the periodic table (e.g. O, S, Se, Te). The II-III-V compound semiconductor material comprises at least one element of group 2 or 12 of the periodic table, at least one element of group 13 of the periodic table, and at least one element of group 15 of the periodic table. For example, the nanocrystals comprise or consist of a sulfide, a selenide, a nitride, or a phosphide.

[0009] According to at least one embodiment, the method comprises using a coordination complex to form an encapsulation surrounding the nanocrystal. The encapsulation can comprise different layers and / or constituents. The encapsulation can be configured or designed as a passivation layer for electronic passivation and / or as a protection layer for protecting the components, e.g. the nanocrystal of the structure, from deterioration. In particular, the encapsulation completely surrounds the nanocrystal. The encapsulation can be in direct contact with the nanocrystal. Alternatively, a further layer can be arranged between the nanocrystal and the encapsulation.

[0010] The coordination complex is a catalyst and is a chemical compound consisting of a central atom or ion, which is usually metallic and is referred to as the coordination center, and a surrounding series of bound molecules or ions, which are in turn referred to as ligands or complexing agents. Many metal-containing compounds, especially those containing transition metals, are coordination complexes. The coordination complex utilizes the catalysis of the deposition on and around the nanocrystal to form the encapsulation. Advantageously, the coordination complex can act as both an acid and a base, and thus the coordination complex can catalyze hydrolysis and polymerization. The coordination complex is preferably added to the total reaction volume in a ratio of 0.05 weight / weight % to 8.5 weight / weight %, including both endpoints.

[0011] According to at least one embodiment, the encapsulation comprises an oxide. The oxide can be, for example, an inorganic oxide or preferably a metal oxide.

[0012] The coordination complex can decompose in the reaction, allowing the central atom (so-called metal) to be incorporated into the encapsulant, resulting in tunable mixed metal oxide stacks with reduced pinhole defects. The coordination complex undergoes hydrolysis and can form an encapsulant, resulting in the possibility of fabricating structures with preferred mixed metal oxides and layered metal oxides. Advantageously, the use of the coordination complex acts to slow down the hydrolysis, thus allowing for conformal oxide growth that encloses the nanocrystals.

[0013] According to at least one embodiment, the method for producing a structure comprises: providing a nanocrystal, the nanocrystal being configured to convert primary radiation into secondary radiation; forming an encapsulant enclosing the nanocrystal using a coordination complex, wherein the encapsulant comprises an oxide.

[0014] The concept of the present application is to provide a method for producing a structure, wherein the structure comprises a nanocrystal encapsulated by a metal oxide encapsulant without significantly impairing the photoluminescence quantum yield (PLQY) of the nanocrystal. The photoluminescence quantum yield, as one criterion for a successful down-converter, is significantly and positively affected during the oxide encapsulation using the method described herein.

[0015] Furthermore, the lifetime under conditions such as LED operating conditions is improved.

[0016] Furthermore, the encapsulant provides improved protection during stress testing when compared to non-encapsulated nanocrystals. This can further improve the quality of the encapsulant by tuning its chemical composition and chemical properties.

[0017] Furthermore, the method described herein slows down the hydrolysis of the oxide, resulting in a conformal encapsulant enclosing the nanocrystal for optimal barrier protection.

[0018] According to at least one embodiment, the nanocrystal comprises or consists of a semiconductor material, and the semiconductor material is a II-VI compound semiconductor material or a III-V compound semiconductor material. Preferably, the nanocrystal is free of cadmium.

[0019] According to at least one embodiment, the nanocrystal comprises a core and at least one shell. In particular, the nanocrystal is a quantum dot comprising a core and at least one shell. The core and / or the shell can comprise at least one semiconductor material. In particular, the core comprises a different semiconductor material than the shell. For example, the at least one shell is epitaxially grown on the core. The nanocrystal can comprise further shells and / or layers. For example, the nanocrystal comprises a quantum well structure. For example, the nanoparticle is a core-shell quantum dot or a core-shell-shell quantum dot. Preferably, the quantum dot is free of cadmium.

[0020] In a preferred embodiment, the quantum dots are III-V compound semiconductor materials.

[0021] According to at least one embodiment, the metal of the coordination complex is selected from the group of: an alkali metal, an alkaline earth metal, a transition metal, or a post-transition metal. Post-transition metals are located in the periodic table between the transition metals on the left and the chemically weak, non-metallic metalloids on the right. These metals are soft, have poor mechanical strength, and generally have a lower melting point than transition metals. In other words, the metal of the coordination complex is selected from the group of: an alkali metal, an alkaline earth metal, a transition metal, and / or Al, Ga, In, Tl, Sn, Pb, Bi, Po. Preferably, the metal of the coordination complex is selected from Al, Zr, Cu, and Ti. The coordination complex comprises a metal coordinated by at least one ligand. The ligands can be different from each other. The metal of the coordination complex can form an encapsulant as a metal oxide. In other words, the metal of the coordination complex forms an oxide of the encapsulant.

[0022] According to another embodiment, the method for forming an encapsulant surrounding nanocrystals further comprises using an oxide precursor selected from: tetraethyl orthosilicate; tetramethyl orthosilicate; tetrabutyl orthosilicate; or tetrapropyl orthosilicate; a silane having an amino, a mercapto, a phosphonic acid, an isocyanate, an aldehyde, or a carboxyl head group; and combinations thereof. The silane having an amino, a mercapto, a phosphonic acid, an isocyanate, an aldehyde, or a carboxyl head group can also be a silane-containing ligand on the nanocrystal for a conformal encapsulant. This means that on the surface, the nanocrystal comprises an intermediate layer comprising the silane having an amino, a mercapto, a phosphonic acid, an isocyanate, an aldehyde, or a carboxyl head group.

[0023] Preferably, the Si-metal of the oxide precursor forms an oxide of the encapsulant. For example, the oxide precursor is tetraethyl orthosilicate, and this oxide precursor forms a Si-oxide encapsulating the nanocrystals.

[0024] According to at least one embodiment, the coordination complex is a hydrolysis and polymerization catalyst for forming siloxanes. This enables the oxide precursor (e.g. tetraethyl orthosilicate) to be converted into silicon dioxide while largely maintaining the photoluminescence quantum yield of the nanocrystals. Advantageously, only little harmful interaction between the coordination complex and the nanocrystals occurs.

[0025] According to another embodiment, the oxide is selected from the group consisting of: mixed metal oxides and / or metal oxides, wherein the metal is derived from the metal of the coordination complex and / or the metal is derived from the oxide precursor. This means, for example, that the oxide is a metal oxide or a mixed metal oxide. The mixed metal oxide can be obtained from the metal of the coordination complex and the metal of the oxide precursor. Alternatively, the mixed metal oxide can be obtained from at least two coordination complexes which differ in their metal or at least two oxide precursors which differ in their metal.

[0026] In other words, if the oxide precursor is, for example, tetraethyl orthosilicate and the coordination complex is an aluminum complex, the mixed metal oxide can be an aluminosilicate. For example, the metal of the oxide differs from the metal of the coordination complex. For example, the oxide is selected from the group consisting of: silicon dioxide (Si02), aluminum oxide (AI2O3), titanium dioxide (Ti02), zirconium oxide (Zr02), aluminosilicates, and combinations thereof.

[0027] According to at least one embodiment, the ligand of the coordination complex is selected from the group consisting of: alkoxy, acetylacetonate ligand (acac), ammine ligand, diketone, hydride ligand, aquo ligand, ethylacetoacetate ligand, acetylacetonate derivative, and combinations thereof. Preferably, the ligand is a bidentate ligand. For example, the coordination complex comprises a metal and at least one ligand, wherein the ligands can differ from each other, for example.

[0028] According to at least one embodiment, the coordination complex is a late transition metal diketone.

[0029] According to one preferred embodiment, the coordination complex is an acetylacetonato metal. Preferably, the coordination complex is an aluminum acetylacetonate (AI(acac)3).

[0030] Advantageously, the acetylacetonato metal utilizes catalytic nanocrystals (e.g., quantum dots) on and deposition (e.g., silica deposition) around the nanocrystals (e.g., quantum dots) to form an encapsulant. The current understanding of how acetylacetonato metals catalyze hydrolysis and polymerization relies on their ability to act as both an acid and a base. This is different from other bases used to deposit encapsulants (e.g., silica) on and around nanocrystals.

[0031] Furthermore, the acetylacetonato metal undergoes hydrolysis or alcoholysis and forms an encapsulant comprising a metal oxide, resulting in the possibility of fabricating structures with preferred mixed metal oxides and layered metal oxides. Advantageously, the use of acetylacetonato metals acts to slow down the hydrolysis, thus allowing for the growth of conformal metal oxides around the nanocrystals.

[0032] According to at least one embodiment, an intermediate layer is arranged between the encapsulant and the nanocrystal. The intermediate layer is selected from the group consisting of a silane-terminated ligand, a hydroxide-terminated ligand, or a combination thereof. In other words, the intermediate layer comprises a silane-terminated ligand as well as a hydroxide-terminated ligand. The intermediate layer serves to functionalize the surface of the nanocrystal for obtaining a more conformal encapsulant. The head group of the material of the intermediate layer attached to the surface of the nanocrystal can include an amino group, a mercapto group, a phosphonic acid group, an isocyanate group, an aldehyde group, or a carboxylic acid group.

[0033] According to at least one embodiment, the encapsulant individually encapsulates the nanocrystal. This means that each nanocrystal is covered by one encapsulant. The encapsulant is preferably free of pinholes or pathways. The encapsulant almost completely surrounds the nanocrystal. Preferably, the encapsulant completely surrounds the nanocrystal. Individually encapsulated nanocrystals can be obtained by adding a surfactant such as AOT or Igepal via micelle formation. For example, the surfactant is added to the nanocrystal and to the coordination complex.

[0034] According to at least one embodiment, the encapsulant comprises a plurality of sub-layers forming a shell surrounding the nanocrystal. The plurality of sub-layers can comprise the same metal oxide. Preferably, the plurality of sub-layers comprises different metal oxides and / or mixed metal oxides. In other words, the oxide sub-layer deposition can be repeated many times, resulting in sub-layers that are more effective barriers than a single thick layer. This includes, for example, the initial coordination complex catalyzed material providing improved stability.

[0035] According to another embodiment, at least two adjacent sub-layers comprise different oxides. For example, one sub-layer comprises or consists of SiO2, while the adjacent sub-layer comprises or consists of a metal oxide (e.g. AI2O3). In other words, one of the sub-layers is formed from an oxide precursor, and one of the sub-layers is formed from a metal of the coordination complex. For example, at least one sub-layer of the encapsulant comprises silicon dioxide. It is also possible that one sub-layer comprises or consists of a mixed metal oxide (e.g. aluminosilicate).

[0036] According to at least one embodiment, one of the sub-layers is formed from a coordination complex, and / or one of the sub-layers is formed from an oxide precursor. This means that the oxide of the sub-layer comprises the same metal as the metal of the coordination complex and / or the metal of the oxide precursor. For example, the metal of the coordination complex is aluminum and the oxide of the sub-layer is aluminum oxide, and / or the metal of the oxide precursor is Si and the oxide of the sub-layer is Si02. Furthermore, this preferably creates a pathway to manufacture mixed metal oxide sub-layers, as the coordination complex itself is prone to hydrolysis and subsequently incorporates into the oxide encapsulate. The use of, for example, multiple acac coordination complexes with different acac ligands enables the formation of a stack of layers for preventing pinholes or pathways through the encapsulate.

[0037] According to at least one embodiment, the encapsulate has a thickness in the range of 0.5 nm to 500 nm, including the two end values. Preferably, the encapsulate has a thickness in the range of 5 nm to 50 nm, including the two end values.

[0038] According to at least one embodiment, at least two nanocrystals are surrounded by the same encapsulate. This means that an aggregate of several nanocrystals can be encapsulated by the same encapsulate. Then, the aggregate is preferably completely covered by the encapsulate. For example, the ratio of solvent, the ratio of coordination complex and nanocrystals can be adjusted to get a single nanocrystal or an aggregate (a cluster of several nanocrystals) in the encapsulate.

[0039] According to at least one embodiment, the formation of the encapsulate surrounding the nanocrystal also uses water. The content of water in the reaction mixture can vary anywhere between 0.001 weight / weight % and 20 weight / weight %, including the two end values. In one preferred embodiment, the content of water is 0.001 weight % to 10 weight %.

[0040] According to at least one embodiment, the formation of the encapsulate surrounding the nanocrystal is initially water-free. The initial catalytic reaction can not be a hydrolysis reaction (e.g. an alcoholysis), but the initial reaction produces water as a byproduct, which can then proceed as a hydrolysis reaction, resulting in an increase in the weight / weight % of water as the reaction proceeds.

[0041] According to at least one embodiment, the formation of the encapsulate surrounding the nanocrystal also uses a solvent in which the nanocrystal and the coordination complex are soluble. The solvent can be a solvent in which all reagents (this means the coordination complex, the nanocrystal, the optional water and the optional oxide precursor) are completely soluble, or a solvent of several mixed but miscible solvents with mixed polarity. The solvent can include cyclohexane, acetone, toluene, acetonitrile, ethanol, isopropanol, methanol, butanol, tetrahydrofuran, or dimethylformamide. In one preferred embodiment, the solvent can be selected from: cyclohexane, acetone, acetonitrile, an alcohol or a combination thereof.

[0042] According to at least one embodiment, the method is carried out in air or it can be carried out in a flow or static inert gas environment, such as argon, nitrogen, etc., under an air-free atmosphere. Furthermore, the method can be carried out at elevated temperatures below the boiling point of the solvent system.

[0043] According to at least one embodiment, the method is carried out in an inert gas environment at a temperature of 25 °C to 100 °C, including the two end values. Preferably, the method is carried out at a temperature of 25 °C to 45 °C, including the two end values. In a preferred embodiment, the method is carried out in an inert atmosphere at a temperature of 35 °C.

[0044] For example, the encapsulation is produced as follows: A nanocrystal or a plurality of nanocrystals is suspended in a solvent and, optionally, in water, to form a first solution. A surfactant and, subsequently, a coordination complex and, optionally, an oxide precursor are added to the first solution to initiate oxide growth on the surface of the nanocrystal, thereby forming the encapsulation.

[0045] Furthermore, the structure is specified. In particular, the method for producing the structure described herein produces the structure. Therefore, embodiments, features and advantages described in connection with the method for producing the structure also apply to the structure and vice versa.

[0046] According to at least one embodiment, the structure comprises a nanocrystal configured to convert primary radiation into secondary radiation, and the encapsulation at least partially surrounding the nanocrystal encapsulation comprises an oxide. Advantageously, the structure has a good photoluminescence quantum yield and improved lifetime under conditions such as LED operating conditions. The encapsulation protects the nanocrystal during stress tests.

[0047] According to at least one embodiment, the encapsulation comprises a plurality of sub-layers. In other words, the plurality of sub-layers forms the encapsulation. The plurality of sub-layers can be, for example, a mixed metal oxide and / or a metal oxide. The mixed metal oxide is, for example, an aluminosilicate and the metal oxide is, for example, Si02or AI2O3. Other oxides are alkali metal oxides, alkaline earth metal oxides, transition metal oxides or post-transition metal oxides or combinations thereof. The mixed metal oxide can be obtained by a combination of the metal of the oxide precursor and the metal of the coordination complex. The metal oxide can be obtained by the metal of the oxide precursor and / or by the metal of the coordination complex.

[0048] According to at least one embodiment, at least two adjacent sub-layers comprise different oxides. This means that each sub-layer can have a different oxide.

[0049] According to at least one embodiment, the encapsulation comprises traces of substances from the coordination complex. This means that the structure comprises traces of substances from the coordination complex. The traces of substances can be detected with conventional analytical methods.

[0050] Advantageously, the coordination complex slows down the hydrolysis of the metal oxide, which leads to a conformal encapsulation surrounding the nanocrystals for optimal barrier protection.

[0051] Furthermore, optoelectronic devices are described in detail. In particular, the optoelectronic devices comprise at least one structure described herein. Therefore, the embodiments, features and advantages described in connection with the structure and the method for producing the structure also apply to the optoelectronic devices and vice versa.

[0052] According to one embodiment, the optoelectronic device comprises a semiconductor chip configured to emit primary radiation. In other words, the semiconductor chip is configured to emit electromagnetic radiation in a first wavelength range. In particular, the primary radiation has a wavelength in the ultraviolet to blue spectral region.

[0053] According to at least one embodiment, the optoelectronic device comprises a conversion element comprising at least one structure described herein, in particular a plurality of structures. In particular, the conversion element is configured to convert at least a portion of the primary radiation into secondary radiation. In other words, the conversion element converts electromagnetic radiation in a first wavelength range into electromagnetic radiation in a second wavelength range. For example, the first wavelength range and the second wavelength range are at least partially different. For example, the second wavelength range comprises wavelengths having a lower energy compared to the wavelengths in the first wavelength range. In particular, the ability of the conversion element to convert electromagnetic radiation is due to the structures comprising nanocrystals that convert the primary radiation into secondary radiation.

[0054] According to at least one embodiment, the optoelectronic device comprises a semiconductor chip configured to emit primary radiation and a conversion element comprising at least one structure disclosed herein.

[0055] Advantageously, the optoelectronic devices described herein have an improved efficiency, in particular an increased operating lifetime under corrosive conditions, due to the encapsulated nanocrystals. In this way, the conversion element can maintain its conversion efficiency for a longer period of time compared to a conversion element comprising structures without encapsulation. Furthermore, the photoluminescence quantum yield of the encapsulated nanocrystals is advantageously not significantly affected.

[0056] According to at least one embodiment, the semiconductor chip is a micro-LED. Herein and hereinafter, LED is an abbreviation of the term "light-emitting diode". The micro-LED can have a width, length, thickness and / or diameter of less than or equal to 100 micrometers, in particular less than or equal to 70 micrometers, for example less than or equal to 50 micrometers. In particular, the edge length of the light-emitting surface of the micro-LED, for example in a plan view of the layers of the layer stack, is less than or equal to 70 micrometers, for example less than or equal to 50 micrometers. For example, the micro-LED is a light-emitting diode, wherein the growth substrate is removed, such that the thickness of the micro-LED is for example 1.5 micrometers to 10 micrometers, and including 1.5 micrometers and 10 micrometers. For example, the micro-LED is provided on a wafer having releasable holding structures. The micro-LED can be separated from the wafer in a non-destructive manner.

[0057] According to at least one embodiment, the conversion element comprises a matrix material and at least one structure, in particular a plurality of structures, embedded in the matrix material. For example, the matrix material is silicone, polysiloxane, or epoxy resin. In this case, the conversion element is formed as a layer or a cast body. The at least one structure is preferably uniformly distributed in the matrix material.

[0058] According to at least one embodiment, the conversion element consists of a structure comprising nanocrystals and encapsulants, wherein the structure is embedded in a matrix material. In this case, the conversion element is formed as a layer or a cast body.

[0059] According to at least one embodiment, the optoelectronic component is used in augmented reality and / or virtual reality applications, in automotive applications, in down-converters, in sensors, for illumination, and / or in other applications.

[0060] Advantageous embodiments and developments of the method for producing a structure, the structure and the optoelectronic component will become apparent from the exemplary embodiments described below in conjunction with the attached drawings.

[0061] In the drawings, like reference numerals generally refer to like parts throughout the various views. The drawings are not necessarily to scale, with emphasis generally being placed upon illustrating the principles of the disclosure. In the following description, various aspects of the disclosure are described in reference to the drawings, in which:

[0062] Figure 1 A schematic diagram of a method for producing a structure according to one exemplary embodiment is shown;

[0063] Figure 2 , Figure 3 and Figure 4 Each shows a schematic diagram of a method for producing a structure according to a different exemplary embodiment;

[0064] Figure 5 , Figure 6 and Figure 7 each shows a schematic of a structure according to a different exemplary embodiment;

[0065] Figure 8 and Figure 9 each shows a schematic of an optoelectronic device according to a different exemplary embodiment; and

[0066] Figure 10 shows photoluminescence quantum yields of structures according to one exemplary embodiment and comparative examples.

[0067] In the exemplary embodiments and figures, like or similarly acting structural parts are provided with the same reference signs. The dimensions of the elements shown in the figures and their mutual dimensional relationships should not be considered as being true to scale. Rather, the individual elements can be represented in an enlarged dimension for the purpose of better representability and / or for the purpose of better understanding.

[0068] Figure 1 shows a schematic of a method for producing a structure 1 according to one exemplary embodiment. A coordination complex 4 and a nanocrystal 2 are provided and a reaction mixture is formed. The nanocrystal 2 is configured to convert primary radiation into secondary radiation. Further, water 9, a solvent 13 and an oxide precursor 7 are optionally part of the reaction mixture. An encapsulant 3 is formed that surrounds the nanocrystal 2, wherein the encapsulant 3 comprises an oxide. The nanocrystal 2 can be, for example, a nanoparticle, a phosphor or a quantum dot. Preferably, the nanocrystal 2 comprises or consists of a semiconductor material, and the semiconductor material is a II-VI compound semiconductor material or a III-V compound semiconductor material. For example, the semiconductor material does not contain cadmium. The coordination complex 4 consists of at least one metal 5 and at least one ligand 6. The metal 5 is selected from the group of an alkali metal, an alkaline earth metal, a transition metal or a post-transition metal. The ligand 6 of the coordination complex 4 is selected from the group of an alkoxy group, an acetylacetonate ligand (acac), an ammine ligand, a diketone, a hydride ligand, a water ligand, an ethylacetoacetate ligand, an acetylacetonate derivative and combinations thereof.

[0069] Preferably, the coordination complex 4 is an acetylacetonato metal. Particularly preferably, the coordination complex 4 is an acetylacetonato aluminum. The oxide precursor 7 is selected from the group of tetraethyl orthosilicate; tetramethyl orthosilicate; tetrabutyl orthosilicate; tetrapropyl orthosilicate; a silane having an amino, a mercapto, a phosphonic acid group, an isocyanate group, an aldehyde group, or a carboxyl head group; and combinations thereof.

[0070] Coordination complex 4 serves as a catalyst for catalyzing the formation of structure 1. Coordination complex 4 itself hydrolyzes to form encapsulation 3, which is a metal oxide. Furthermore, coordination complex 4 may also form mixed metal oxides and layered metal oxides surrounding nanocrystal 2. The oxides are selected from mixed metal oxides and / or metal oxides, wherein the metal is derived from metal 5 of coordination complex 4 and / or the metal is derived from oxide precursor 7. An intermediate layer (not shown) may be formed between nanocrystal 2 and encapsulation 3. The intermediate layer is selected from silane-terminated ligands, hydroxide-terminated ligands, or combinations thereof. Encapsulation 3 encapsulates a single nanocrystal 2. Encapsulation 3 has a thickness ranging from 0.5 nm to 500 nm, including two end values. The method is carried out in an inert gas atmosphere at a temperature of 25°C to 45°C.

[0071] Figure 2 A schematic diagram of a method for producing structure 1 according to an exemplary embodiment is shown. Water 9, tetraethyl orthosilicate as oxide precursor 7, nanocrystals 2, and acetylacetone-based metal (M(acac)3) as coordination complex 4 are mixed together. The reaction is carried out in an airless environment and under flowing or still inert gas conditions (argon, nitrogen, etc.). This can be carried out at a temperature below the boiling point of the solvent system. In a preferred embodiment, it is carried out at a temperature of 35°C under an inert atmosphere. Furthermore, a solvent 13 selected from cyclohexane, acetone, toluene, acetonitrile, ethanol, isopropanol, methanol, butanol, tetrahydrofuran, or dimethylformamide is added. Coordination complex 4 catalyzes the reaction and forms an encapsulation 3 surrounding the nanocrystals 2. In this exemplary embodiment, the encapsulation 3 is SiO2 or can be a mixed metal oxide, such as aluminosilicate. An intermediate layer (not shown here) may be formed between the nanocrystals 2 and the encapsulation 3.

[0072] The coordination complex 4 comprises a metal 5 selected from the group consisting of alkali metals, alkaline earth metals, transition metals, or post-transition metals. Furthermore, the coordination complex 4 comprises a ligand 6 selected from the group consisting of alkoxy groups, acetylacetone ligands (acac), amino ligands, diketones, hydrogen ligands, aqueous ligands, ethylacetoacetic acid ligands, acetylacetone derivatives, and combinations thereof. Figure 2 In an exemplary implementation, the ligand is an acetylacetone ligand or a diketone.

[0073] Figure 3 A schematic diagram of a method for producing structure 1 according to an exemplary embodiment is shown. Figure 3 and Figure 2 The difference lies in that the encapsulation 3 covers three nanocrystals 2. In other words, at least two nanocrystals 2 are surrounded by the same encapsulation 3. In this case, the encapsulation 3 can be SiO2.

[0074] Figure 4 A schematic diagram of a method for producing a structure 1 is shown according to one exemplary embodiment. Figure 4 In contrast to Figure 2 and Figure 3 The structure 1 comprises nanocrystals 2 and at least two sub-layers 8. The encapsulation 3 comprises a plurality of sub-layers 8 forming a shell around the nanocrystals 2. At least two adjacent sub-layers 8 comprise different oxides. One oxide of the sub-layers 8 is formed from a metal 5 of the coordination complex 4, and one oxide of the sub-layers 8 is formed from an oxide precursor 7. In particular, the nanocrystals 2, preferably quantum dots, are surrounded by SiO2, such that the first sub-layer 8 is SiO2, the second sub-layer 8 is a metal oxide sub-layer 8 and can be formed from the coordination complex 4, and the third sub-layer 8 is SiO2, a metal oxide or a mixed metal oxide.

[0075] Figure 5 A schematic diagram of a structure 1 is shown according to one exemplary embodiment. The structure 1 comprises nanocrystals 2 configured to convert primary radiation into secondary radiation and an encapsulation 3 at least partially surrounding the nanocrystals 2, and wherein the encapsulation 3 comprises an oxide. The nanocrystals 2 can be quantum dots and can comprise a core and a shell. The core and / or the shell comprise at least one semiconductor material. The semiconductor material is for example a III-V compound semiconductor material or a II-VI compound semiconductor material. In particular, the core comprises a different semiconductor material than the shell. The nanocrystals 2 can comprise further shells and / or layers. For example, the nanocrystals 2 comprise a semiconductor material that does not contain cadmium, and the encapsulation 3 is SiO2. The SiO2 encapsulation 3 is formed from an oxide precursor 7.

[0076] Figure 6 A schematic diagram of a structure 1 is shown according to one exemplary embodiment. The structure 1 comprises nanocrystals 2 and an encapsulation 3. The encapsulation 3 is in contact with the nanocrystals 2 and covers the nanocrystals 2 almost completely. The encapsulation 3 comprises a plurality of sub-layers 8. At least two adjacent sub-layers 8 comprise different oxides. A first sub-layer 8 closer to the nanocrystals 2 is SiO2, a second sub-layer 8 between the first sub-layer 8 and a third sub-layer 8 is a metal oxide, for example aluminum oxide, and the third sub-layer 8 is SiO2, a metal oxide or a mixed metal oxide, for example an aluminosilicate. The encapsulation 3 has a thickness in the range of 0.5 nm to 500 nm, including the two end values. The exact layering, order and number of layers are only exemplary embodiments, and many other combinations are possible.

[0077] Figure 7A schematic diagram of a structure 1 described herein is shown according to one exemplary embodiment. The structure 1 comprises a plurality of nanocrystals 2 and an encapsulant 3 surrounding the plurality of nanocrystals 2. The encapsulant 3 is identical for the plurality of nanocrystals 2. The encapsulant 3 can be SiO2and the nanocrystals 2 are cadmium-free quantum dots. If the coordination complex 4 is Al(acac)3, then the encapsulant 3 can be AI2O3or aluminosilicate.

[0078] Figure 5 Figure 6 and Figure 7 SiO2is included as encapsulant 3 or as sublayer 8, but other metal oxides are possible, either as homogeneous mixture and as dispersed, or as layered structure.

[0079] Figure 8 A schematic diagram of an optoelectronic device 10 described herein is shown according to a first exemplary embodiment. The optoelectronic device 10 comprises a semiconductor chip 11 configured to emit primary radiation of a first wavelength range. The semiconductor chip 11 can be a micro-LED, for example with the first wavelength range being in the blue spectral region. A conversion element 12 is arranged on a radiation exit surface of the semiconductor chip 11. The conversion element 12 can be arranged directly on the radiation exit surface or at a distance from the radiation exit surface. The conversion element 12 can be in the form of a layer or a cast. The conversion element 12 converts the primary radiation into secondary radiation of a second wavelength range. The conversion element 12 comprises or consists of at least one structure 1 described herein.

[0080] For example, the conversion element 12 comprises at least one structure 1 as shown in connection with Figure 5 Figure 6 and Figure 7 In particular, the at least one structure 1 can be embedded in a matrix material such as silicone, polysiloxane or epoxy resin.

[0081] Figure 9 A schematic diagram of an optoelectronic device 10 described herein is shown according to a second exemplary embodiment. The second exemplary embodiment essentially corresponds to the first exemplary embodiment shown in Figure 8 In comparison to the first exemplary embodiment, the semiconductor chip 11 and the conversion element 12 are arranged in a recess of a housing. The conversion element 12 comprises a structure 1 in the form of a cast surrounding the semiconductor chip 11 as shown in connection with Figure 8

[0082] Figure 10 A schematic diagram of an optoelectronic device 10 described herein is shown according to a third exemplary embodiment. The third exemplary embodiment essentially corresponds to the first exemplary embodiment shown in Figure 5 ​​​Photoluminescence quantum yield, PLQY, of Structure 1 of the exemplary embodiments and comparative examples shown in the figures. The comparative examples describe Structure 1 without encapsulant 3. In more detail, the comparative examples are Structure 1 comprising quantum dots.

[0083] In Figure 10 the figures, the photoluminescence quantum yield is plotted against the running time t in minutes. Curve 10-1 shows the photoluminescence quantum yield as a function of time for Structure 1 comprising quantum dots and encapsulant 3. Curve 10-2 shows the photoluminescence quantum yield as a function of time for a comparative example of a structure without encapsulant 3. As can be seen in Figure 10 , the luminescence of Structure 1 comprising encapsulant 3 (curve 10-1) can be maintained longer than the luminescence of the structure without encapsulant 3 (curve 10-2). Without encapsulant 3, the photoluminescence quantum yield decreases rapidly after a short amount of time (curve 10-2), while the photoluminescence quantum yield of Structure 1 with encapsulant 3 decreases only slightly over a significantly longer period of time (curve 10-1). These measurements were obtained with a blue light irradiation of 60 mW / cm 2 .

[0084] In the table listed below, the initial photoluminescence quantum yield of one exemplary embodiment is shown in relation to a comparative example. Furthermore, two different encapsulation methods are compared. The Structure 1 of the exemplary embodiment comprises nanocrystals 2 and encapsulant 3. The coordination complex 4 used for the synthesis is Al(acac)3, and the oxide of the encapsulant 3 is SiO x . The Structure 1 of the comparative example comprises nanocrystals 2 and SiO x encapsulant 3, while the encapsulant 3 is obtained by a coordination complex-free method. It can be shown that the PLQY retention and the powder PLQY of the Structure 1 of the exemplary embodiment are much higher compared to the Structure 1 of the comparative example. Furthermore, it can be seen that a Structure 1 according to one exemplary embodiment with one SiO x sublayer 8 and a Structure 1 according to one exemplary embodiment with two SiO x sublayers 8 show almost the same PLQY.

[0085]

[0086] According to further exemplary embodiments, the features and exemplary embodiments described in connection with the figures can be combined with each other, even if not all combinations are explicitly described. Furthermore, the exemplary embodiments described in connection with the figures can have alternative or additional features as described in the general part.

[0087] As used herein, the ordinal adjectives “first,” “second,” “third,” etc. merely designate different instances of a similar object, and do not imply that the objects so designated must be in a given order, in time, in space, in

[0088] The present disclosure is not limited to the described example embodiments by virtue of the description based on the example embodiments. Rather, the present disclosure encompasses any novel feature and also encompasses any combination of features, particularly any combination of features in the patent claims and in the example embodiments, even if that feature or combination is not expressly stated in the patent claims or in the example embodiments.

[0089] This patent application claims priority to U.S. Patent Application 63 / 580,716, the disclosure of which is hereby incorporated by reference.

[0090] Legend of reference signs

[0091] 1 structure

[0092] 2 nanocrystal

[0093] 3 encapsulant

[0094] 4 coordination complex

[0095] 5 metal

[0096] 6 ligand

[0097] 7 oxide precursor

[0098] 8 sublayer

[0099] 9 water

[0100] 10 optoelectronic device

[0101] 11 semiconductor chip

[0102] 12 conversion element

[0103] 13 solvent

[0104] 10-1 comparative example curve

[0105] 10-2 example embodiment curve

Claims

1. A method for producing a structure (1), comprising: providing nanocrystals (2) configured to convert primary radiation into secondary radiation, forming an encapsulation (3) surrounding the nanocrystals (2) using a coordination complex (4), wherein the encapsulation (3) comprises an oxide.

2. The method according to the preceding claim, wherein the nanocrystals (2) comprise or consist of a semiconductor material, and the semiconductor material is a II-VI compound semiconductor material or a III-V compound semiconductor material.

3. The method according to one of the preceding claims, wherein the metal (5) of the coordination complex (4) is selected from the group of: an alkali metal, an alkaline earth metal, a transition metal, or a post-transition metal.

4. The method according to one of the preceding claims, wherein forming the encapsulation (3) surrounding the nanocrystals (2) further comprises using an oxide precursor (7) selected from: tetraethyl orthosilicate; tetramethyl orthosilicate; tetrabutyl orthosilicate; tetrapropyl orthosilicate; a silane having an amino, a mercapto, a phosphonic acid, an isocyanate, an aldehyde, or a carboxyl head group; and combinations thereof.

5. The method according to one of the preceding claims, wherein the oxide is selected from: a mixed metal oxide and / or a metal oxide, wherein the metal originates from the coordination complex (4) and / or the metal originates from the oxide precursor (7).

6. The method according to one of the preceding claims, wherein the ligand (6) of the coordination complex (4) is selected from: an alkoxy, an acetylacetonate ligand (acac), an ammine ligand, a diketone, a hydride ligand, a water ligand, an ethylacetoacetate ligand, an acetylacetonate derivative, and combinations thereof.

7. The method according to one of the preceding claims, wherein the coordination complex (4) is an acetylacetonato metal.

8. The method according to one of the preceding claims, wherein an intermediate layer is formed between the encapsulation (3) and the nanocrystal (2), and the intermediate layer is selected from: a silane-terminated ligand, a hydroxide-terminated ligand, or a combination thereof.

9. The method according to one of the preceding claims, wherein the encapsulation (3) encapsulates one nanocrystal (2) individually.

10. The method according to one of the preceding claims, wherein the encapsulation (3) comprises a plurality of sub-layers (8) forming a surrounding of the nanocrystal (2).

11. The method according to the preceding claim, wherein at least two adjacent sub-layers (8) comprise different oxides.

12. The method according to one of the preceding claims, wherein one of the sub-layers (8) is formed from the coordination complex (4), and / or one of the sub-layers (8) is formed from the oxide precursor (7).

13. The method according to one of the preceding claims, wherein at least two nanocrystals (2) are surrounded by the same encapsulation (3).

14. The method according to one of the preceding claims, wherein the encapsulation (3) surrounding the nanocrystal (2) is also formed using water (9) and / or a solvent (13) in which the nanocrystal (2) and the coordination complex (4) are soluble.

15. The method according to one of the preceding claims, wherein the method is carried out in an inert gas atmosphere at a temperature of 25 °C to 100 °C.

16. A structure (1) comprising: - a nanocrystal (2) configured to convert primary radiation into secondary radiation, and - an encapsulation (3) at least partially surrounding the nanocrystal (2), and wherein the encapsulation (3) comprises an oxide.

17. The structure (1) according to the preceding claim, wherein the encapsulation (3) comprises a plurality of sub-layers (8).

18. The structure (1) according to one of the preceding claims, wherein at least two adjacent sub-layers (8) comprise different oxides.

19. The structure (1) according to one of the preceding claims, wherein the encapsulation (3) comprises at least trace amounts of substances from the coordination complex (4).

20. An optoelectronic device (10) comprising: - a semiconductor chip (11) configured to emit primary radiation; and - a conversion element (12) comprising at least one structure (1) according to one of claims 16 to 19. ​

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