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Definitions

• the present disclosure relates to an optoelectronic component and a method for producing an optoelectronic component.
• LED light-emitting diode
• laser diode laser diode
• crosstalk refers to how much light, generated by one pixel, spreads through a conversion element to neighboring pixels. Further requirements on conversion elements of pixelated lighting applications are, for example, color uniformity and thermal stability.
• Phosphor-in-silicone, phosphor-in-glass, and phosphor- on-glass down-converting elements can accommodate multiple phosphor compositions, i.e. phosphor blends, with some restrictions, but the phosphor-in/on-glass options require a glue layer with the disadvantages mentioned above.
• nitride hosts nitride hosts.
• the nitrides are easily damaged when exposed to elevated temperatures in air. Even the lowest melting glasses require hundreds of degrees Celsius to make them flowable, so it is not straightforward to include a nitride phosphor in glass without at least some damage being done to the
• red phosphors are easily mixed into standard silicone matrixes, those matrixes are not stable under the high heat and flux conditions needed.
• Micro-pixelated lighting applications with a pixel size of approximately 300 ym require conversion elements to be very thin, i.e. £ 20 ym. Such a low thickness creates
• an optoelectronic component comprises a semiconductor chip comprising a multiplicity of pixels, each pixel emitting electromagnetic primary radiation from a radiation exit surface, wherein on at least a part of the radiation exit surfaces conversion layers are applied, wherein the
• conversion layers comprise a crosslinked matrix having a three-dimensional siloxane-based network and at least one phosphor embedded in said matrix, wherein the conversion layers have a thickness of £ 30 ym, preferably £ 20 ym.
• the electromagnetic primary radiation may be a visible radiation or an invisible radiation. According to one
• the electromagnetic primary radiation is a visible radiation, for example with wavenlengths in the blue
• the pixels of the semiconductor chip may emit the same electromagnetic primary radiation.
• the conversion layer is to be understood as a layer that absorbs, at least partially, the electromagnetic primary radiation and then emits an electromagnetic secondary radiation.
• the wavelength ranges of the primary and the secondary radiation can be distinct from each other or there could be a significant overlap between the absorbed and the emitted wavelengths.
• the absorption and the emission of wavelength is performed by the at least one phosphor incorporated in the conversion layer.
• the electromagnetic secondary radiation comprises wavelengths being longer than the wavelength of the
• conversion layer is a down-conversion layer.
• the conversion layer may according to one embodiment be made separately on a substrate, for example, and then incorporated into the optoelectronic component in a subsequent step.
• it is produced in situ on each pixel of the semiconductor chip of the optoelectronic component .
• the pixels of the semiconductor chip are to be understood as individually controllable portions of the semiconductor chip, each emitting electromagnetic primary radiation. According to one embodiment all pixels emit blue radiation.
• the conversion layers being applied on at least a part of the radiation exit surfaces are, according to one embodiment, in direct mechanical contact to the semiconductor chip.
• Each conversion layer comprises a size conforming to the size of one pixel, i.e., to the cross-section of one pixel.
• each conversion layer is in mechanical contact with only one pixel of the semiconductor chip.
• the optoelectronic component is a micro-pixelated optoelectronic component.
• each pixel may have a size of £ 300 ym in length.
• the conversion layer of the optoelectronic component fulfils all of the requirements for the application in a pixelated, especially a micro-pixelated, light source.
• it has a thickness of £ 30 ym, preferably £ 20 ym, and is placed directly on the radiation exit surface of the semiconductor chip. Further, it provides a broad spectrum of emitted wavelength providing a color-on-demand by the possibility to incorporate one phosphor or a blend of phosphors. Its
• the crosstalk between the pixels is minimized compared to a situation where a converter layer has to be glued on a semiconductor chip.
• the color uniformity from pixel-to-pixel is also improved with this conversion layer. Allowable differences in color points from pixel-to-pixel could vary by application and pixel resolution, but as with other light sources, it is desired that most people would not be able to tell the difference between the colors of the light generated by different pixels. A rough guideline would be that all the pixels within the device should have color points that fit within a three-step MacAdam ellipse. This is challenging for conversion layers, especially down conversion layers,
• the pixels comprise a pixel- to-pixel period of £ 125 ym.
• component may be a micro-pixelated lighting application.
• the crosslinked matrix comprises an organic content of less than 40 wt% of the conversion layer.
• the organic content is less than or equal to 20 wt% of the conversion layer.
• the organic content is about 15 wt%.
• the reduced organic content can be obtained by an increased number of crosslinks in the matrix and a reduced number of side chains by using a (poly) siloxane that is based, primarily, on T-unit bonding.
• D-unit and T-unit refer to the relative number of oxygen and carbon atoms bonded to each silicon atom in the (poly) siloxane .
• a D-unit describes the bonding situation where the silicon atom is bonded to two oxygens and two carbons.
• a T-unit describes the bonding situation where the silicon atom is bonded to three oxygens and one carbon.
• the thermal stability may be a long-term temperature stability even at temperatures of more than 200
• R 1 and R 2 are - independently from each other - chosen from a group consisting of alkyl, alkoxy, aryl, aryloxy, alkenyl, substituted alkyl, substituted alkoxy, substituted aryl, substituted aryloxy, substituted alkenyl, and combinations thereof,
• R 11 , R 12 and R 13 are - independently from each other - chosen form a group consisting of H, alkyl, alkoxy, aryl, aryloxy, alkenyl, substituted alkyl, substituted alkoxy, substituted aryl, substituted aryloxy, substituted alkenyl, and
• R 3 and R 4 are - independently from each other - chosen from a group consisting of alkoxy, vinyl, hydroxyl, carboxylic acid, ester, H, alkyl, aryl, substituted alkoxy, substituted carboxylic acid, substituted ester, substituted vinyl, substituted alkyl, substituted aryl, and combinations
• R 1 and R 2 and R 11 , R 12 and R 13 comprise an alkoxy content being in the range from 10 wt% to 50 wt% of the total formula.
• the precursor material for the crosslinked matrix comprises a substituted polysiloxane precursor or a substituted polysilazane precursor.
• the backbone of the polysiloxane precursor comprises alternating silicon and oxygen atoms
• the backbone of the polysilazane precursor comprises alternating silicon and nitrogen atoms.
• the precursor is a liquid at room temperature if it is a polysiloxane. In some cases, a small amount of solvent is needed for the polysilazane precursor for it to be in liquid- type form.
• the three-dimensional network is formed from the liquid or solution-based precursor. When cured, the material is a highly cross-linked network, primarily made up of siloxane bonds.
• R 1 and R 2 and, respectively, R 11 , R 12 and R 13 are according to one embodiment chosen from a group consisting of methyl, methoxy, ethyl, ethoxy, phenyl, phenoxy, vinyl, and trifluoropropyl .
• R 1 and R 2 and, respectively, R 11 , R 12 and R 13 are independently from each other methyl and methoxy.
• R 1 and R 2 and, respectively, R 11 , R 12 and R 13 comprise an alkoxy content, for example a methoxy content, in the range of from 10 wt% to 50 wt%, advantageously in the range of 15 wt% to 45 wt%, even more advantageously in the range of 20 wt% to 40 wt%.
• a repeating unit of a precursor may comprise the generic formula, wherein the number of repeat units n can vary and an exemplary methoxy content is about 32 wt%:
• polysilazane backbone with alkyl, for example methyl, and alkoxy, for example methoxy, side groups is possible as well.
• alkyl for example methyl
• alkoxy for example methoxy
• side groups there could be a silicon atom being substituted with two methyl groups or two methoxy groups as long as the total alkoxy content of all precursor compounds in the precursor material falls within the above-mentioned ranges to have enough reactive groups for building the cross-linked matrix .
• the precursor material can also be partially reacted and comprise an exemplary structure as shown in the generic formula :
• the dangling bonds could indicate a continuation of the structure or a terminal group. In a partially reacted
• the methoxy content will be lower than for the unreacted precursor, and the viscosity can thus be higher.
• terminal groups of the polysiloxane precursor and the polysilazane precursor i.e. R 3 and R 4 , comprise according to an embodiment independently from each other chemically reactive groups such as for example alkoxy, vinyl, hydroxyl, carboxylic acid, ester, or any other of the reactive
• terminal groups known from organic chemistry field.
• the terminal groups could be less
• reactive such as hydrogen, methyl, ethyl or any other alkyl or aryl groups .
• the properties of the matrix and, thus, of the conversion layer can be tuned by modifying the precursor material.
• the reactive group is an alkoxy group which can be equally represented by R 1 , R 2 , R 11 , R 12 , and/or R 13 .
• the terminal groups R 3 and R 4 can be varied as well as the number of repeating units n. Even with this number n, the properties of the matrix material can be changed. For example, a lower n will generally lead to a lower viscosity and a higher n will lead to a higher viscosity of the
• the repeating number n is according to one embodiment chosen such that the viscosity of the precursor is in the range of 1 to 150 mPas, advantageously in the range of 1 to 60 mPas, and even more advantageously in the range of 2 to 40 mPas .
• the viscosity of the precursor is in the range of 1 to 150 mPas, advantageously in the range of 1 to 60 mPas, and even more advantageously in the range of 2 to 40 mPas .
• methyl methoxy polysiloxane may be less than 40 mPas .
• low molecular weight precursors are provided.
• n might be chosen to be ⁇ 10. Due to the relatively low viscosity of the precursor a high
• T 1 and T 2 represent terminal groups being equal to R 3 and R 4 of the above-shown generic formula.
• P 1 , P 2 , P 3 and P 4 are side groups.
• the P-groups and T-groups could all be the same, e.g. a methyl group.
• each functional group could be a different group.
• some of the groups could be the same and some could be different.
• one of the groups could be made up of more than one functional group. All the definitions for substituents and properties correspond to the definitions and properties as mentioned with respect to the generic formulae of the precursor material shown above.
• P 2 is either a methyl, a phenyl or a combination of the two
• P 1 is ethyl, with an ethoxy content of 10 to 50 wt%, but more preferably 20 to 30 wt%, and a viscosity in the range of 30 to 70 mPas .
• a small amount of solvent may be present in this embodiment.
• P 2 is a combination of methyl and phenyl
• P 1 is a methyl group.
• a methoxy content of 10 to 20 wt% is preferred, along with a viscosity of 50 to 150 mPas .
• the crosslinked matrix comprises a three-dimensional siloxane-based network having the generic formula
• each R is - independently from each other - chosen from a group consisting of a group listed for R 1 , R 2 , R 3 , R 4 , R 11 , R 12 , R 13 , or any combination thereof, and the dangling bonds are - independently from each other - representative of a continuation of the network or one of the groups listed for R 1 , R 2 , R 3 , R 4 , R 11 , R 12 , R 13 .
• the material may result independently if a polysiloxane precursor or a polysilazane precursor is used to form the matrix material.
• the three-dimensional siloxane-based network is a cured material.
• the precursor material is any material that is easy to visualize, but it is not meant to be technically accurate.
• the methoxy groups would result in crosslinking, for example. Some of them might remain intact and some of them might be replaced by silanol groups.
• the precursor material is any material that is easy to visualize, but it is not meant to be technically accurate.
• the methoxy groups would result in crosslinking, for example. Some of them might remain intact and some of them might be replaced by silanol groups.
• the precursor material is any material that is easy to visualize, but it is not meant to be technically accurate.
• the methoxy groups would result in crosslinking, for example. Some of them might remain intact and some of them might be replaced by silanol groups.
• At least one additive that is chosen from a group consisting of catalysts, nanoparticles, metal- organic compounds, organic molecules, organic polymers, inorganic polymers, and combinations thereof.
• the precursor material generally is a liquid
• the additives can serve different purposes, such as controlling the viscosity during the fabrication, providing crack resistance and enhanced mechanical strength, tuning the refractive index or increasing the thermal connectivity.
• the catalyst comprises a titanium alkoxide, for example tetra-n-butyl titanate. This is a typical catalyst for the curing of a precursor to a
• crosslinked matrix additionally to water or humidity.
• the tetra-n-butyl titanate may not be strictly necessary since the presence of liquid water or gaseous humidity is sometimes sufficient for the curing step to get a crosslinked matrix depending on the embodiment.
• a typical amount of the catalyst being added to the precursor material may be from 0.5 wt% to 5 wt% .
• additives can be added to the precursor material in order to influence the processability of the precursor and/or the final properties of the highly crosslinked matrix and, thus, of the conversion layer.
• the nanoparticles can be chosen from a group consisting of oxides, like silicon dioxide
• SiCy zirconium dioxide
• ZrCy zirconium dioxide
• TiCy titanium dioxide
• AI2O3 aluminum oxide
• ZnO zinc oxide
• nitrides like aluminum nitride (AIN) , silicon nitride (SZ3N4) , or boron nitride (BN) , carbon-based nanoparticles, like carbon
• nanotubes, graphene or their derivatives heteropoly acides like 12-tungstophosphoric acid (H3PW12O40) and 12- tungstosilicic acid (H4SZW12O40) and any combinations thereof.
• heteropoly acides like 12-tungstophosphoric acid (H3PW12O40) and 12- tungstosilicic acid (H4SZW12O40) and any combinations thereof.
• fumed silica additionally comprises fumed silica.
• the content of fumed silica may be in the range of 5 wt% to 40 wt%, preferably between 15 wt% and 35 wt%. The given ranges are to be
• fumed silica may be added as additive, in order to thicken the slurry of precursor and phosphor after the addition of the at least one phosphor.
• Other nanoparticles may be added to change the refractive index or thermal conductivity, for example .
• the surfaces of the inorganic nanoparticles are modified with capping agents to make them miscible with the precursor compound.
• the metal-organic compounds are chosen from a group consisting of titanium alkoxides,
• zirconium alkoxides aluminum alkoxides, silicon alkoxides, halfnium alkoxides, and any combination thereof.
• the organic molecules are chosen from a group consisting of adhesion promotors, plasticizers, de-foamers, thickeners, or thinners .
• the organic polymers and the inorganic polymers are chosen from a group consisting of poly (dimethyl siloxane) , poly (methylphenyl siloxane) , poly (diphenyl siloxane), poly (silphenylene-siloxane) , polyphosphazenes , polysilazane, perhydropolysilazane .
• precursor may depend on criteria like the size of the
• the precursor material additionally comprises some D-unit type bonding, wherein the content of the D-unit bonding is between 0 mol% and 30 mol% of all the siloxane units.
• D-unit bondings where a silicon atom is bonded to two oxygen atoms may be present.
• the precursor material has a molecular weight of less than 3000 g/mol, preferably less than 100 g/mol.
• the at least one phosphor is chosen from a group consisting of (REi_ x Ce x) 3 (Al 4-y A' y) 5O12 with 0 ⁇ x £ 0.1 and 0 £ y £ 1, (REi_ x Ce x) 3 (Al 5- 2 y Mg y Si y) O12 with 0 ⁇ x £ 0.1 and 0 £ y £ 2, (REi_ x Ce x) 3Al 5-y Si y Oi2- y N y with 0 ⁇ x £ 0.1 and 0 £ y £ 0.5, (REi_ x Ce x) 2CaMg 2 Si30i2 : Ce 3+ with 0 ⁇ x £ 0.1, (AEi_ x Eu x) 2Si5Ns with 0 ⁇ x £ 0.1, (AEi_ x Eu x) AlSiN3 with 0 ⁇ x £ 0.1, (AEi_ x Eu x) 2
• the phosphor may be added to the precursor material in the form of a powder.
• concentration of the phosphor or the phosphor blend may be equal to or smaller than 90 wt% of the mixture, for example in the range of 15 wt% to 75 wt%, of the phosphor-in-polysiloxane or phosphor-in-polysilazane
• top surface facing away from the semiconductor chip and a bottom surface facing the semiconductor chip, wherein the top surface and/or the bottom surface is
• Structured means in this context that the surface is modified, for example to improve the outcoupling of light.
• the structured surface comprises random roughness, a microlense, a microlense array, a micro optic, a photonic crystal, a plasmonic array, a meta lense, aperiodic nanostructured arrays, a dielectric film, a stack of dielectric films, or a graded index anti-reflective coating.
• the stack of dielectric films comprises for example anti-reflective coatings, dichroic filters, and wavelength or angle-dependent pass filters.
• the surface modifications may be imparted to the conversion layer during its production either by starting with a
• the optoelectronic component is an LED or a laser diode.
• the method comprises the steps of providing a semiconductor chip with a
• each pixel emitting electromagnetic primary radiation from a radiation exit surface, preparing a starting mixture comprising at least one phosphor and a precursor material, wherein the precursor material comprises a precursor having a structure that is chosen from one of the generic formulae
• R 1 and R 2 are - independently from each other - chosen from a group consisting of alkyl, alkoxy, aryl, aryloxy, alkenyl, substituted alkyl, substituted alkoxy, substituted aryl, substituted aryloxy, substituted alkenyl, and combinations thereof,
• R 11 , R 12 and R 13 are - independently from each other - chosen form a group consisting of H, alkyl, alkoxy, aryl, aryloxy, alkenyl, substituted alkyl, substituted alkoxy, substituted aryl, substituted aryloxy, substituted alkenyl, and
• R 3 and R 4 are - independently from each other - chosen from a group consisting of alkoxy, vinyl, hydroxyl, carboxylic acid, ester, H, alkyl, aryl, substituted alkoxy, substituted carboxylic acid, substituted ester, substituted vinyl, substituted alkyl, substituted aryl, and combinations
• n is chosen such that the viscosity of the precursor is in the range of 1 to 150 mPas
• R 1 and R 2 and R 11 , R 12 and R 13 comprise an alkoxy content being in the range from 10 wt% to 50 wt%
• a conversion layer being applied on at least a part of the radiation exit surfaces, comprising a crosslinked matrix comprising the phosphor dispersed in said matrix, wherein the conversion layer is applied in a thickness of £ 30 ym, preferably £ 20 ym.
• the method is suitable to produce an optoelectronic component according to the above-mentioned embodiments.
• This method is an inexpensive process which is conductable at room temperature to produce an optoelectronic component with a conversion layer.
• the starting mixture can be applied directly on the pixels of the semiconductor chip and thus the conversion layer is produced in situ on each pixel or on the desired pixels of the semiconductor chip. "Applying the starting mixture onto at least a part of the radiation exit surfaces of the pixels” is to be understood that the starting mixture is applied separately on each pixel of the semiconductor chip, namely on the radiation exit surface of each pixel or on the radiation exit surface of the pixels where a conversion layer is desired.
• the starting mixture is applied on a temporary substrate, cured on the temporary substrate, and glued to the radiation exit surface of at least one of the pixels of the semiconducting chip, wherein, after gluing, the temporary substrate is removed.
• the starting mixture is applied on a temporary substrate and cured to form a conversion layer with a thickness of £ 30 ym.
• This conversion layer is glued on the radiation exit surface of at least one pixel of the semiconductor chip and could be glued to as many as all of the pixels of a given pixelated semiconductor chip and, after gluing, the temporary substrate is removed.
• a solvent can be used or a solvent-free approach can be performed.
• at least one phosphor is mixed into the precursor material.
• a solvent may or may not be added to the starting mixture. If a solvent is needed, many organic solvents will work, such as for example xylene or butyl acetate.
• At least one additive is added to the starting mixture, said additive being chosen from a group consisting of catalysts, nanoparticles, metal- organic compounds, organic molecules, organic polymers, inorganic polymers and combinations thereof.
• the additives may be chosen from additives mentioned above with respect to the optoelectronic component.
• the application of the starting mixture onto at least a part of the radiation exit surfaces of the pixels or on the temporary substrate takes place by a method chosen from a group consisting of screen printing, stencil printing, spray coating, and ink jetting. With these methods an exact application of the conversion layer material onto the single pixels is possible.
• the portions of the semiconductor chip where no starting mixture is to be applied can be coated with a photoresist or capped with a patterned cover, for example.
• a local application of the starting mixture is even possible.
• the curing takes place at room temperature or at elevated temperatures.
• the curing time can be reduced by exposing the starting mixture to elevated temperatures for a few hours.
• the curing takes place when exposing the starting mixture to water or humidity.
• During the curing alcohol may be produced as a by-product leading to a densification of the matrix material .
• the application of the starting mixture onto at least a part of the radiation exit surfaces is repeated at least once.
• Figure 1 shows a schematic cross-section of an optoelectronic component
• Figure 2 shows a schematic top view on an optoelectronic component
• Figure 3 shows thermogravimetric analysis profiles of a comparative matrix material and matrix material of a
• Figure 1 shows a schematic cross-section of an optoelectronic component having a substrate 30, a semiconductor chip 20 being pixelated and conversion layers 10.
• the pixel-to-pixel period may be £ 125 ym.
• the size of a pixel may be in the range of 300 ym.
• the optoelectronic component may be an LED package or a laser diode-based light source. Not explicitly shown in Figure 1 are the active layer sequence of the semiconductor chip 20 and additional elements like a housing or a reflective sealing material surrounding the semiconductor chip 20.
• the semiconductor chip emits a primary electromagnetic radiation, for example, in the near-UV to blue spectrum. Each pixel of the semiconductor chip 20 is individually
• the conversion layer 10 absorbs the primary electromagnetic radiation at least partially and converts it to a secondary radiation being different from the primary radiation.
• the emission of light of each pixel is composed of the combination of primary and secondary radiation.
• the wavelength of the secondary radiation depends on the phosphor or blend of phosphors embedded in the matrix of the conversion layer.
• Each conversion layer may have a different secondary radiation, i.e. the emission of light from each pixel may be different from other pixels.
• the conversion layers 10 are applied on the radiation exit surface of the pixels of the semiconductor chip, the
• a methoxymethyl polysiloxane is made or purchased as a precursor material.
• the methoxy content should be in the order of 10 to 50 wt%, preferably in the range of 15 to 45 wt%, even more preferably in the range of 30 to 40 wt%.
• the molecular weight should be such that the viscosity is in the range of 1 to 50 mPas, but preferably in the range of 2 to 40 mPas .
• Other polysiloxanes or polysilazanes with various substituents as mentioned above are possible as well.
• a YAG:Ce-type phosphor would be chosen as a down conversion material to be incorporated into the precursor material to prepare a starting mixture.
• the phosphor mixture could be a blend of cerium-activated, lutetium aluminum garnet (Lui- x Ce x) 3AI5O12, where 0 ⁇ x £ 0.2, and an europium- activated, calcium aluminum silicon nitride (Cai_ x Eu x) AlSiN3 where 0 ⁇ x £ 0.2 may be provided as phosphor powders to be incorporated to the liquid precursor material.
• other phosphors or blends of phosphors as mentioned above are possible as well, depending on the application and color targets .
• the concentration, and ratio of the phosphors depends on the cerium and europium concentrations, the phosphors absorbances and quantum efficiencies, the target thickness of the
• the ratio of garnet to nitride phosphor is typically within the range of 2.5:1 to 4.5:1.
• additives may be added to the starting mixture comprising the precursor and the phosphor blend or the phosphor blend.
• a solvent may be added or fumed silica may be added if a thickening of the slurry is desired.
• Other additives may be added additionally or alternatively in order to change the refractive index or thermal conductivity.
• a hardener such as a titanium alkoxide may be added in the range of 0.5 wt% to 5 wt%.
• the slurry comprising the starting mixture, is sprayed onto the pixelated semiconductor chip 20 where the phosphor concentration and layer thickness are chosen to hit the target color point, but the final thickness of the conversion layer must remain at or below the 30 ym height limit.
• the starting mixture may be cured at room temperature or elevated temperatures to form a highly cross-linked matrix with the phosphors embedded therein.
• the curing can take place after the exposure to water or humidity.
• the spraying is performed separately, i.e. the pixels of the semiconductor chip 20 are provided with a conversion layer 10 separately from each other .
• the application of the starting material onto the pixels of the semiconductor chip 20 generally can be performed by methods like screen printing, stencil printing, spray coating or ink jetting.
• Figure 2 refers to a top view of an optoelectronic component where the top surfaces of the conversion layers 10 are shown.
• One of the conversion layers 10 is applied onto a pixel of the semiconductor chip 20, wherein this central pixel is on. This pixel is indicated by hatches in Figure 2.
• the semiconductor chip 20 comprises a 7x7 array of micro-pixels. Crosstalk among the pixels of the semiconductor chip is measured by how much light can be detected at
• the desired value of crosstalk is accomplished, that is the brightness measured at a pixel with a distance of two pixels between this pixel and the hatched pixel is not greater than 200 times less than the brightness of the hachted pixel.
• This low crosstalk is realized by the low thickness of £ 30 ym of the conversion layer 10 as well as its direct application on the semiconductor chip 20.
• Figure 3 shows a thermogravimetric analysis profile of a comparative methyl-based silicone (II) in comparison to a methyl-based polysiloxane (I) .
• the x-axis shows the
• the standard silicone reference (II) loses almost 60% of its weight indicating a large organic content.
• the polysiloxane material (I) loses less than 20% of its weight indicating a significantly lower organic content. This leads to the enhanced thermal stability of the conversion layer in comparison to analogous materials based on standard optical silicone matrixes.

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