CONVERTER ELEMENT, METHOD FOR PRODUCING A CONVERTER ELEMENT AND RADIATION EMITTING DEVICE

Abstract

A converter element is provided, comprising a first conversion region comprising a first phosphor, a second conversion region comprising a second phosphor, wherein the first phosphor has upon excitation a faster radiation decay lifetime than the second phosphor, wherein at least one of the first and second phosphor is embedded in a matrix material, wherein the matrix material comprises a three-dimensionally crosslinked polysiloxane having an organic content of less than 40 wt %. Further, a method for producing a converter element and a radiation emitting device are provided.

Claims

1. A converter element, comprising: a first conversion region comprising a first phosphor, a second conversion region comprising a second phosphor, wherein the first phosphor has upon excitation a faster radiation decay lifetime than the second phosphor, wherein at least one of the first and second phosphor is embedded in a matrix material, wherein the matrix material comprises a three-dimensionally crosslinked polysiloxane having an organic content of less than 40 wt %.

2. The converter element according to claim 1, wherein the three-dimensionally crosslinked polysiloxane comprises repeating units of the formula [RSiO.sub.3/2].sub.x[R.sub.2SiO].sub.y[R.sub.3SiO.sub.1/2].sub.z wherein x+y+z=1, 0<x≤1, 0≤y<1, 0≤z<1, and each R is independently from each other chosen from an organic functional group having a carbon atom as bonding atom.

3. The converter element according to claim 1, wherein one of the first and the second phosphor is embedded in the matrix material and wherein the other one of the first and the second phosphor is one of a ceramic phosphor, a single crystal phosphor and a phosphor-in-glass.

4. The converter element according to claim 1, wherein the second phosphor is embedded in the matrix material and the first phosphor is one of a ceramic phosphor, a single crystal phosphor and a phosphor-in-glass.

5. The converter element according to claim 1, wherein the first conversion region and/or the second conversion region comprises a first phase being free of phosphor and a second phase comprising the phosphor.

6. The converter element according to claim 1, wherein the first conversion region and the second conversion region comprise a common boundary or wherein the first conversion region and the second conversion region are glued together.

7. The converter element according to claim 1, wherein the first conversion region is a first conversion layer and the second conversion region is a second conversion layer, wherein the first and second conversion layers are stacked.

8. The converter element according to claim 1, wherein the first conversion region is a first conversion layer comprising at least one recess, wherein the second conversion region is arranged in the at least one recess.

9. The converter element according to claim 8, wherein the recess comprises at least one of a hole and a partial groove.

10. The converter element according to claim 1, wherein the first conversion region comprises a multiplicity of loose portions which are embedded in the second conversion region.

11. The converter element according to claim 1, wherein the first conversion region and/or the second conversion region comprise structured surfaces.

12. A method for producing a converter element comprising the steps of: preparing a first conversion region comprising a first phosphor, preparing a second conversion region comprising a second phosphor, and combining the first and the second conversion region, wherein the first phosphor has upon excitation a faster radiation decay lifetime than the second phosphor, wherein at least one of the first and the second conversion region is prepared by providing a polysiloxane precursor, embedding the first or the second phosphor in the polysiloxane precursor to create a mixture, curing the mixture, wherein a matrix material comprising a three-dimensionally crosslinked polysiloxane having an organic content of less than 40 wt % and the first or the second phosphor being embedded therein is produced.

13. The method according to claim 12, wherein the polysiloxane precursor comprises repeating units of the formula [(R)(OR)SiO].sub.x[R.sub.2SiO].sub.y[R.sub.3SiO.sub.1/2].sub.z wherein x+y+z=1, 0<x≤1, 0≤y<1, 0≤z<1, and each R is independently from each other chosen from an organic functional group having a carbon atom as bonding atom, wherein an alkoxy content is in a range of 10 wt % to 50 wt % and/or wherein the precursor comprises a number of repeating units such that a viscosity of the precursor is less than 150 mPas.

14. The method according to claim 12, wherein preparing the first conversion region and preparing the second conversion region are successively conducted.

15. The method according to claim 14, wherein combining the first conversion region and the second conversion region comprises gluing.

16. The method according to claim 12, wherein before curing the mixture is applied on a surface by a method chosen from spraying, tape-casting, doctor-blading, spin coating, dispensing, and casting.

17. The method according to claim 12, wherein preparing the first conversion region comprises forming a first conversion layer and wherein preparing a second conversion region comprises forming a second conversion layer.

18. A radiation emitting device, comprising: a semiconductor chip which, during operation, emits electromagnetic radiation in a first wavelength range from a radiation exit surface, and a converter element according to claim 1 on the radiation exit surface converting the electromagnetic radiation of the first wavelength range into an electromagnetic radiation of a second wavelength range.

19. The radiation emitting device according to claim 18, wherein the first conversion region of the converter element is closer to the semiconductor chip than the second conversion region.

20. The radiation emitting device according to claim 18, wherein the converter element is glued to the semiconductor chip or wherein the converter element is applied in a remote configuration to the semiconductor chip.

Description

[0079] Advantageous embodiments and developments of the converter element, the method for producing the converter element, and the radiation emitting device will become apparent from the exemplary embodiments described below in conjunction with the figures.

[0080] FIGS. 1 to 6 show schematic cross sectional views of converter elements according to various embodiments.

[0081] FIGS. 7a and 7b show schematic cross sectional views of radiation emitting devices according to various embodiments.

[0082] FIG. 8 shows the relative power loss of an exemplary embodiment and reference examples.

[0083] FIG. 9 shows a spectral power distribution of an exemplary embodiment and a reference example.

[0084] FIG. 10 shows a spectral power distribution of an exemplary embodiment and a reference example.

[0085] FIG. 11 shows thermogravimetric analysis profiles of an exemplary embodiment and a reference example.

[0086] In the exemplary embodiments and figures, similar or similarly acting constituent parts are provided with the same reference symbols. The elements illustrated in the figures and their size relationships among one another should not be regarded as being true to scale. Rather, individual elements may be represented with an exaggerated size for the sake of better representability and/or for the sake of better understanding.

[0087] FIG. 1 shows a schematic cross sectional view of a converter element 1 containing a first conversion region 10 and a second conversion region 20. In this exemplary embodiment both conversion regions 10 and 20 are formed as layers that are stacked. At least one of the conversion regions 10, 20 comprises a matrix material being a three-dimensionally crosslinked polysiloxane and a phosphor embedded therein. One of the conversion regions 10 and 20 can be an inorganic conversion region being formed of a ceramic phosphor, a single crystal phosphor or a phosphor-in glass.

[0088] In the following the first conversion region 10 will be described as an inorganic first conversion region 10 comprising a ceramic first phosphor 11, and the second conversion region 20 will be described as containing a second phosphor 21 being embedded in the matrix material 22. However, this is not to be understood as limiting. Rather, even both conversion regions 10, 20 can comprise the matrix material 22 with an embedded phosphor or the second conversion region 20 can comprise a ceramic phosphor while the first conversion region 10 comprises the matrix material 22 with an embedded first phosphor 11. Independently of the composition of the conversion regions 10 and 20, the first phosphor 11 in the first conversion region 10 has a faster radiation decay lifetime upon excitation than the second phosphor 21 contained in the second conversion region 20.

[0089] FIG. 2 shows the converter element 1 of FIG. 1 in more detail. First conversion region 10 is formed of the first phosphor 11, which is in this exemplary embodiment a ceramic phosphor, for example a Ce-doped ceramic phosphor which has a one or to orders of magnitude faster radiation decay lifetime than an Eu-doped phosphor. Second conversion region 20 comprises the matrix material 22 in which the second phosphor 21, for example an Eu-doped phosphor, is embedded. The second phosphor 21 is a phosphor powder comprising particles, which are embedded in the matrix material 22. The second phosphor 21 could also be a blend of different phosphors, all having a slower radiation decay lifetime than the first phosphor 11. For example, the second phosphor 21 is an Eu-doped phosphor which provides a high spectral flexibility of the converter element 1. The converter element 1 is a hybrid converter element.

[0090] FIG. 3 shows a schematic cross sectional view of another exemplary embodiment of the converter element 1. While second conversion region 20 corresponds to second conversion region 20 of FIG. 2, first conversion region 10 is formed of a composite material with a luminescent second phase 13 being formed of the ceramic first phosphor 11, for example a Ce-doped phosphor, and a non-luminescent first phase 12, both phases being a dense sintered body. The non-luminescent phase 12 comprises silica, alumina, or any oxide garnet, spinel, or silicate. Any other inorganic material that has a relatively high thermal conductivity but low absorption in the visible region of the spectrum can be chosen as well.

[0091] FIG. 4 shows a schematic cross sectional view of another exemplary embodiment. In contrast to the FIGS. 1 to 3, where first and second conversion regions 10, 20 are in direct mechanical contact, here, the first conversion region 10 and the second conversion region 20 are glued to each other. Thus, bonding layer 30 is between the first and second conversion regions 10 and 20. The bonding layer 30 comprises or consists of a glue like silicone, filled silicone, siloxane, or filled siloxane.

[0092] In FIGS. 1 to 4 the first and the second conversion regions 10, 20 are formed as layers. FIGS. 5a and 5b show exemplary embodiments where the first conversion region 10 is formed as a layer but comprises structures, and the second conversion region 20 is arranged in the structures. According to FIG. 5a the first conversion region 10 comprises two holes 14 ranging from one surface of the first conversion region 10 to the opposite surface of the first conversion region 10. The second conversion region 20 is arranged in the holes 14 so that one compact converter element 1 is formed. According to FIG. 5b partial grooves 15 are formed in the first conversion region 10 and the second conversion region 20 is arranged in the partial grooves 15. Thus, the second conversion region 20 is not necessarily continuously formed in one piece.

[0093] FIG. 6 shows a cross sectional view of another exemplary embodiment. Here, second conversion layer 20 is formed as a layer and comprises the matrix material 22 and the second phosphor 21. Additionally, it comprises loose portions of first conversion regions 10 being in this example formed of the ceramic first phosphor 11. The loose portions are larger than the phosphor particles 21 but smaller than a non-crushed first conversion region 10.

[0094] In the following the production of an exemplary embodiment of a converter element 1 is explained. In this example the converter element 1 is formed for using it in high CRI (color rendering index) warm-white applications.

[0095] As first conversion region 10 a layer of the ceramic phosphor 11 of (Lu.sub.1-xCe.sub.x).sub.3(Al.sub.1-yGa.sub.y).sub.5O.sub.12 where 0<x≤0.1 and 0≤y≤1 is made according to any known method for making ceramic layers of such a material. For the second conversion region 20 a second phosphor powder 21 of (Sr.sub.yCa.sub.1-x-yEu.sub.x)AlSiN.sub.3 where 0<x≤0.1 and 0≤y≤1-x is provided. For producing the matrix material 22, a polysiloxane precursor, in this example methyl methoxy polysiloxane with a methoxy content between 10% and 50%, preferably between 30% and 40%, is provided and mixed with the second phosphor 21. Before curing this mixture, fumed silica may be added in a range of up to 30 wt % with respect to the total precursor material. The precursor material should be chosen such that it comprises more than 85%, more preferably 100% T-unit type functional monomers. The second phosphor powder 21, the methyl methoxy polysiloxane, and optionally fumed silica are thoroughly mixed together, and a small amount of catalyst or hardener, i.e. 0.05 to 5 wt % with respect to the precursor material, is added. A wide range of hardeners can be applied, in particular titanium alkoxides, amine-containing bases, or combinations thereof.

[0096] The so prepared mixture is applied to one surface of the ceramic first conversion region 10 by spraying, or some other suitable method such as tape-casting, doctor blading, spin coating, casting, or dispensing. The applied mixture is allowed to cure in ambient conditions for several hours up to several days, before the second conversion region 20 and, thus, the converter element 1, is finished. The converter element 1 can in a further step incorporated into a radiation emitting device.

[0097] The total thickness of the converter element 1 should be between 30 μm to 500 μm inclusive, for example 30 μm and 300 μm inclusive, in particular the thickness should be less than 200 μm. The ceramic first conversion region 10 should make up between 20% and 95% of the total thickness of the converter element 1, in particular between 50% and 90%.

[0098] The converter element 1 is incorporated in a radiation emitting device 100, in particular it is arranged on a radiation exit surface of a semiconductor chip 40 of the device. To reduce saturation and optimize thermal management, the ceramic first conversion region 10 should be the region or layer being closer to the semiconductor chip 40 so that the first phosphor 11 having the faster radiation decay lifetime is closer to the semiconductor chip 40 than the second phosphor 21. The ceramic first conversion region 10, in particular if made of Ce-doped materials, can sustain higher fluxes and also helps dissipate heat.

[0099] The exemplary embodiment of the method for producing the converter element 1 is suitable to produce the converter element 1 as shown in FIG. 1 or 2, for example. Upon slight modifications of the method any other converter element as shown in 3 to 6 can be produced similarly.

[0100] Further, various other materials can be used for the production of the converter element 1. As first or second phosphor one or more phosphors as listed above can be chosen. Instead of a ceramic the first phosphor can be a single crystal phosphor or a phosphor-in-glass. The polysiloxane precursor does not necessarily have methyl side groups, but any combination of alkyl and aryl groups are possible as well, as long as the alkoxy content ranges from 10 wt % to 50 wt % in order to get a matrix material 22 having less than 40 wt %, preferably less than 20 wt % organic content. Further the number of siloxane monomer units of the polysiloxane precursor should be in a range such that the viscosity is less than 150 mPas, preferably less than 40 mPas.

[0101] Further, additives may be added to the precursor material in order to change a property such as the viscosity of the mixture or the refractive index, the thermal conductivity or the mechanical hardness of the cured matrix material 22.

[0102] FIGS. 7a and 7b show schematic cross sectional views of radiation emitting devices 100 according to exemplary embodiments. Both figures show a housing 50 with a recess in which a semiconductor chip 40 is arranged. In FIG. 7a the converter element 1 is directly arranged on the semiconductor chip 40 and, thus, on the radiation exit surface 41. Converter element 1 and chip 40 are optionally surrounded by a encapsulant 60, being a transmissive, non-absorbing material, that even fills the recess. FIG. 7b shows a remote configuration where converter element 1 is arranged on top of the housing 50 and optionally the encapsulant 60 and, thus, with a certain distance to the semiconductor chip 40 and the radiation exit surface 41. The semiconductor chip 40 is according to an example a blue emitting LED chip. Any converter element 1 as described with respect to FIGS. 1 to 6 can be applied to the radiation emitting device 100.

[0103] Independently of the configuration of the radiation emitting device 100, the converter element 1 should be applied to the semiconductor chip 40 and the radiation exit surface 41 such that the first conversion region 10 is closer to the chip 40 than the second conversion region 20. Thus, saturation of the second phosphor 21 can be reduced and the thermal management through the converter element 1 can be optimized.

[0104] FIG. 8 shows the relative power loss P of a known Ce-doped ceramic Ce:LuAG 2 (solid circle), an Eu-doped phosphor Eu:β-SiAlON 3 in the matrix material (hollow squares) and a hybrid converter element 1 (hollow diamonds) combining the Ce-doped ceramic in a first conversion region 10 and the Eu-doped phosphor in a second conversion region 20. Current I in A versus the power loss P relative to the ceramic 2 is shown. It can be observed that despite the converter element 1 contains an Eu-doped phosphor having a slow radiation decay lifetime, the loss at high currents I is just 2% higher than in the pure ceramic 2. Compared to this the Eu-doped phosphor in matrix material drops its emission 19% to 20% at about 3 A due to saturation losses. This shows that saturation can be reduced by combining the second conversion region 20 with a ceramic first conversion region 10 and by choosing a phosphor with fast radiation decay lifetime as the first phosphor being closer to the excitation source, i.e. the semiconductor chip 40.

[0105] FIG. 9 shows spectra of the ceramic 2 and the converter element 1 of FIG. 8. Wavelength λ in nm versus spectral power distribution SPD in a.u. is shown. The inset shows an optical image of a cross section of the converter element 1 which is 1.5 mm wide and 250 μm thick. The first and second conversion regions 10,20 are separated by bonding layer 30 between them. By adding more or less of each material the spectra of the converter element 1 and of the ceramic 2 can be tuned to be narrower and thus increase the lumen equivalent value.

[0106] FIG. 10 shows the spectral power distribution SPD in a.u. in dependence of wavelength λ in nm for a ceramic phosphor 2′ which is Ce:YAG emitting cold white light and for a converter element 1 comprising in this example an Eu-doped red-emitting nitride and the matrix material. By using such a converter element 1 it is possible to obtain a device that emits a warmer white (lower CCT, correlated color temperature) while keeping the Ce-doped material close to the excitation source, i.e. the semiconductor chip 40, and thus reducing the effects of saturation. This example shows, that by combining different phosphors in the converter element 1 a high spectral flexibility can be realized while saturation can be reduced.

[0107] FIG. 11 shows thermogravimetric analysis profiles of a cured methyl-based silicone reference D (based on D-units) along with a cured methyl-based polysiloxane T (based on T-units) as used for the here described matrix material. The reference D was cured using the vendors recommended method, and the example T was likewise cured according to the recommended method. Each sample was analyzed by thermogravimetric analysis (TGA) the plots of which are shown in FIG. 11, showing the wt % in dependence of temperature Temp in ° C. The reference sample D lost about 60% of its mass, which corresponds to its organic content. The example T, i.e. the here described matrix material, lost less than 20% of its mass indicating a significantly lower organic content. This large difference in organic content is an important factor as to why the reference sample is not suitable for use in high temperature applications, but the here described matrix material is more thermally stable.

[0108] The features and exemplary embodiments described in connection with the figures can be combined with each other according to further exemplary embodiments, even if not all combinations are explicitly described. Furthermore, the exemplary embodiments described in connection with the figures may have alternative or additional features as described in the general part.

[0109] The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.

REFERENCES

[0110] 1 converter element

[0111] 2 Ce:LuAG ceramic

[0112] 2′ Ce:YAG ceramic

[0113] 3 Eu:β-SiAlON in matrix material

[0114] 10 first conversion region

[0115] 11 first phosphor

[0116] 12 first phase

[0117] 13 second phase

[0118] 14 hole

[0119] 15 partial groove

[0120] 20 second conversion region

[0121] 21 second phosphor

[0122] 22 matrix material

[0123] 30 bonding layer

[0124] 40 semiconductor chip

[0125] 41 radiation exit surface

[0126] 50 housing

[0127] 60 encapsulant

[0128] 100 radiation emitting device

[0129] I current

[0130] P power loss

[0131] λ wavelength

[0132] SPD spectral power distribution

[0133] Temp temperature

[0134] wt % weight percent

[0135] T T-unit based example

[0136] D D-unit based reference