Converter system

Abstract

The invention relates to a converter system, for instance for a light emitting device, comprising: a first material, which comprises, preferably essentially consists of an emitting material, emitting a color of interest, and is essentially free of sensitizer material, a second sensitizer material, which is essentially free of the first material and absorbs light (is excitable) in the wavelength range of interest and its emission spectrum overlaps at least partly with one or more excitation bands of the first material.

Claims

1. A converter system comprising: a first material, which comprises an emitting material, adapted to emit a color of interest, wherein the first material is essentially free of a sensitizer material; and a second sensitizer material, which is essentially free of the first material and is excitable in the wavelength range of interest and its emission spectrum overlaps at least partly with one or more excitation bands of the first material, wherein the emitting material of the first material comprises one or more of the ions of the group comprising Eu.sup.3+, Tb.sup.3+ and Mn.sup.4+, and wherein the second sensitizer material comprises one or more ions selected out of the group Eu.sup.2+, Pb.sup.2+, Bi.sup.3+ and Ce.sup.3+, wherein the emitting material and the second sensitizer material are disposed in different host lattices, and wherein the converter system is adapted to radiatively excite the second sensitizer material.

2. The converter system according to claim 1, wherein the first material and second sensitizer material are so arranged to each other to allow energy transfer from the second sensitizer material to the light emitting material in the first material.

3. The converter system according to claim 1, wherein the first material comprises a red emitting material.

4. The converter system according to claim 1, wherein the first material is provided as a nanophosphor.

5. The converter system according to claim 1, wherein the first material is provided as nanoparticles.

6. The converter system according to claim 1, wherein the first material is provided as nanoparticles and the average diameter of the nanoparticles is 1 nm and 50 nm.

7. The converter system according to claim 1, wherein the second sensitizer material is excitable in the wavelength range between 380 and 580 nm.

8. The converter system according to claim 1, wherein the second sensitizer material is excitable in the UV-A (between 315 and 400 nm), violet (between 400 and 440 nm), blue (between 440 and 480 nm) or green (between 510 and 560 nm) wavelength range.

9. The converter system according to claim 1, wherein the color of interest of the emitting material is in a higher wavelength range than the wavelength range of interest of the second sensitizer material.

10. The converter system according to claim 1, wherein the second sensitizer material is provided as a nanophosphor.

11. The converter system according to claim 1, wherein the converter system is obtainable by a process comprising dissolving the first material and the second sensitizer material in a solvent, and evaporating the solvent.

12. The converter system according to claim 11, wherein the process involves removing ligands from the first material and/or the second sensitizer material prior to the dissolving.

13. A light emitting device comprising a converter system according to claim 1 and a blue light emitting semiconductor material.

14. A system comprising a converter system according to claim 1, the system being one or more of the following: office lighting systems, household application systems, shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, decorative lighting systems, portable systems, automotive applications, and green house lighting systems.

Description

(1) Further details, features and advantages of the object of the present invention can be obtained from the subclaims and from the following description of the accompanying drawings, in whichby way of exampleseveral embodiments of the device according to the invention are shown, as well as with respect to the examples, which are to be considered as purely illustrative and not limiting. In the drawings:

(2) FIG. 1 shows a first embodiment of a converter system according to the present invention;

(3) FIG. 2 shows a second embodiment of a converter system according to the present invention;

(4) FIG. 3 shows a very schematical cross-sectional view through a nanoparticle according to a third embodiment of the present invention;

(5) FIG. 4 shows a very schematical cross-sectional view through a nanoparticle according to a third embodiment of the present invention;

(6) FIG. 5 shows a very schematical cross-sectional view through a nanoparticle according to a third embodiment of the present invention; and

(7) FIG. 6 shows a very schematical cross-sectional view through a nanoparticle according to a third embodiment of the present invention.

(8) FIG. 7 shows the emission spectrum of a converter system according to the invention and a mixture for comparison purposes when excited by UV light at a wavelength of 300 nm.

(9) Hereinafter the invention is explained by way of examples, which are to be considered purely as illustrative and not as limiting.

(10) FIG. 1 showsvery schematicallya first embodiment of a converter system according to the present invention, in with both the first material 10 and the sensitizer material 20 are provided in the form of nanoparticles. As can be seen from FIG. 1 the surface-to-surface distance between the particles is small enough to allow for energy transfer from the sensitizer material 20 to the first material 10.

(11) However, the undesired charge-transfer quenching usually does not or only seldom occur because here the distance between the sensitizer material and the Eu.sup.3+ of the first material is usually too large.

(12) FIG. 2 showsvery schematicallya second embodiment of a converter system according to the present invention. In this embodiment, the sensitizer material 20 is provided as a bulk material with the first material 10 provided as nanoparticles surrounding the sensitizer material. This approach has been shown to be especially promising if the emission of the sensitizer is also desired in the spectrum of the device, e.g., if the sensitizer material comprises YAG:Ce or the like.

(13) FIGS. 3 to 6 show very schematical cross-sectional views through nanoparticles according to the third to sixth embodiment of the present invention.

(14) In FIG. 3 the nanoparticle has a core formed out of an undoped material 30 with the first material 10 forming a shell around it. It goes without saying that also an alternative embodiment where the sensitizer material forms the shell is an embodiment of the present invention.

(15) In FIG. 4 the sensitizer material 20 forms the core with the first material 10 provided as a shell around the core, in FIG. 5 it is the other way around i.e. the first material 10 forms the core, the sensitizer material 20 the shell.

(16) The embodiment of FIG. 6 shows a more complex structure with the first material 10 forming another shell around the particle of the embodiment of FIG. 5. It goes without saying that also here the roles may be reversed (i.e. the sensitizer material forming the core and the outer shell with the first material in between) or also topologies where undoped material is forming a shell or the core also are a part of the present invention.

(17) In an exemplary embodiment, the sensitizer material may be a blue-excitable yellow-/green-emitting material, while the first material may be a Eu.sup.3+ containing material. The sensitizer and first materials may be combined together to form a mixture, preferably as taught herein above, or are brought together in one of the core-shell structures as described above. Under blue excitation of the mixture, some sensitizer ions transfer their energy to Eu.sup.3+, effectively increasing the excitation probability of Eu.sup.3+ via blue light. Often, not all the sensitizer ions will transfer energy to Eu.sup.3+, but will instead emit (yellow/green) light. Thus, under blue excitation, the mixture may produce strong red emission (due to Eu.sup.3+) but with some residual yellow/green emission, from sensitizer ions. The mixture may be combined with addition yellow/green emitting phosphors (e.g., YAG:Ce, LuAG:Ce, BaSrSiO:Eu, etc.), even in the form of conventional micron-size powders, to create a blended white light emission with the desired optical characteristics such as high lumen equivalent of radiation (LER), correlated color temperature (CCT), and color rendering index (CRI).

(18) In another exemplary embodiment, the sensitizer material is nano-sized YAG:Ce.sup.3+ particles, (e.g. as described in J. Mater. Chem. C, 2017, 5, 12561), while the emitter material are nano-sized (Y,V)PO.sub.4:Eu.sup.3+ particles. The materials may be brought into intimate contact as described above and in the Examples, so as to enhance energy transfer from Ce.sup.3+ to Eu.sup.3+. Under blue excitation of the mixture, some Ce.sup.3+ ions may transfer their energy to Eu.sup.3+, effectively increasing the excitation probability of Eu.sup.3+ for blue light. Often, not all the Ce.sup.3+ ions will transfer energy to Eu.sup.3+, but will instead emit (yellow) light. Thus, under blue excitation, the mixture may produce strong red emission (due to Eu.sup.3+) but with some residual yellow emission (from Ce.sup.3+). The mixture may be combined with additional yellow/green emitting phosphors (e.g., YAG:Ce, LuAG:Ce, BaSrSiO:Eu, etc.), even in the form of conventional micron-size powders, to create a blended white light emission with the desired optical characteristics such as LER, CCT, and CRI.

(19) The mixtures in the previous embodiments, combined with or without conventional other phosphors, may be applied to a primary emitting LED chip via various deposition techniques well known in the art. Commonly, the materials are bound together in a silicone binder, and applied directly to the chip. The combination of primary LED emission (e.g., UV, violet, blue) may be combined with the down-converted emission of the mixture(s) and other phosphors (if provided) to emit, for example, white light of the desired characteristics.

(20) The individual combinations of the ingredients and the characteristics of the embodiments mentioned above are exemplary, the exchange and substitution of the teachings included in this publication with other teachings included in the cited documents are also explicitly contemplated. A person skilled in the art will recognize that variations and modifications of the embodiments described herein and other embodiments may be realized without departing from the spirit and scope of the invention. Accordingly, the above description is to be considered exemplary and not as limiting. The word comprises used in the claims does not exclude other elements or steps. The indefinite article a does not exclude the importance of a plural. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. The scope of the invention is defined in the following claims and the associated equivalents.

(21) The invention will now be further illustrated using the following examples without however being limited thereto.

EXAMPLES

Example 1

(22) A converter system was prepared using nano-size LaPO.sub.4:Ce.sup.3+ particles (nominal diameter of 5 nm) as sensitizer material and nano-size Y(V,P)O.sub.4:Eu.sup.3+ particles of nominal diameter of 10 nm as first material.

(23) The LaPO.sub.4:Ce.sup.3+ particles (3% Ce doping) were synthesized as follows: LaCl.sub.3.Math.6H.sub.2O (9.8 mmol, 3.462 g), CeCl.sub.3.Math.7H.sub.2O (0.2 mmol, 74.52 mg) was dissolved in approximately 10 mL of methanol p.a. in a 100 mL 3-neck round-bottomed flask and acquire a clear solution 10.9 mL, 10.650 g (40 mmol) tributyl phosphate was added methanol was removed from solution under vacuum (Schlenk-line), careful with vacuum 30 mL (32 g) diphenyl ether was added Open system, flush afterwards the water released was removed by the hydrated metal chlorides under vacuum at 105 C. (Schlenk line)water should evaporate around 80-85 C. reaction mixture was cooled down to below 50 C. and add 9.5 mL, 7.41 g (40 mmol) tributylamine to the clear solution (under nitrogen) 7.0 mL of a 2 M solution phosphoric acid was added in dihexyl ether (1.96 g H.sub.3PO.sub.4 was dissolved in 10 mL dihexyl ether under ultrasonification), large vial the mixture was heated to 200 C. for 16 hours and the reaction mixture was cooled to room temperature nanocrystals were separated by centrifuging at 2000 rpm for 5 minutes nanocrystals were washed several times with toluene, careful with adding methanol powder was dried under vacuum

(24) The YVPO.sub.4:Eu.sup.3+ nanoparticles are commercially bought from CAN Gmbh, Hamburg (series X Red Aqua: doping level 7%) and are capped with ethylene glycol.

(25) The LaPO.sub.4:Ce.sup.3+ and Y(V,P)O.sub.4:Eu.sup.3+ nanoparticles were mixed in a 15:1 weight ratio and dissolved in 4 mL isopropanol, stirred for 1.5 hr and then dried at 120 C. in air while stirring, after which the mixed nanoparticles (mixture) are integrated (i.e., clustered) into a white powder. Thus, the different nanoparticles are in intimate contact with one another, such that sensitizer and emitter ions are separated at distances for which energy transfer can efficiently occur.

(26) The converter system obtained was excited by UV light at 300 nm. Excitation and emission spectra were recorded at room temperature using an Edinburgh Instruments FLS920 fluorescence spectrometer. A 450 W Xe lamp was used as excitation source, where the excitation wavelength of interest was selected using a monochromator and the emitted light was detected with a Hamamatsu R928 PMT detector. The measurements were performed on dried powders in reflection mode.

(27) The resulting spectrum is shown in FIG. 7.

Comparative Experiment A

(28) The LaPO.sub.4:Ce.sup.3+ nanoparticles and YVPO.sub.4:Eu.sup.3 + nanoparticles as described in Example 1 were synthesized and dried separate, before loosely mixing them in a dry state in a 15:1 weight ratio. In this case the different nanoparticles are not in intimate contact with one another, such that sensitizer and emitter ions are separated at distances too large for energy transfer to occur.

(29) The resulting mixture was excited by UV light at 300 nm as described in Example 1. The resulting spectrum is shown in FIG. 7.

(30) The spectrum obtained after exciting the converter system according to the invention (example 1) shows an Eu.sup.3+ emission peak that is about 10 times higher than the peak obtained for the mixture prepared in comparative experiment A. This 10 times higher Eu.sup.3+ emission peak shows that exciting the converter system according to the invention (Example 1) resulted in energy transfer. Notably, the peak obtained for the material of comparative experiment A is not the result of energy transfer, but of the direct excitation of the Eu.sup.3+ at 300 nm, which is also observed when simply exciting the Y(V,P)O.sub.4:Eu.sup.3+ material by itself.

(31) The mixture according to the invention (Example 1) may be combined with any number of blue- and yellow-/green-emitting down-conversion materials to generate white light.