Wavelength converter and light-emitting device having same
An alumina-based ceramic wavelength converter is described having a surface layer containing a second phase of alumina, preferably as alumina crystallites. The surface layer is formed as a result of the sintering process used to form the bulk ceramic which is itself substantially transparent. The ceramic wavelength converter is combined with a light emitting diode to form a light emitting device. Preferably, the ceramic wavelength converter is comprised of an alumina-based phosphor represented by a general formula A 3 B 5 O 12 :Ce, wherein A is Y, Sc, La, Gd, Lu, or Tb and B is Al, Ga or Sc.
1. A wavelength converter comprising a solid monolithic piece of a luminescent ceramic material, the ceramic material comprising an alumina-based phosphor capable of converting primary light having a first peak wavelength into secondary light having a second peak wavelength, a bulk portion of the converter being substantially transparent, and the converter having at least one major surface with an as-sintered surface layer having an alumina second phase.
2. The wavelength converter of claim 1 wherein the alumina second phase comprises alumina crystallites.
3. The wavelength converter of claim 1 wherein a thickness of the surface layer is less than about 50 μm.
4. The wavelength converter of claim 1 wherein a thickness of the surface layer is less than about 10 μm.
5. The wavelength converter of claim 1 wherein the converter is a flat plate.
6. The wavelength converter of claim 5 wherein both major surfaces of the plate have the as-sintered surface layer having an alumina second phase.
7. The wavelength converter of claim 5 wherein the converter has a thickness of between 20 μm and 500 μm.
8. The wavelength converter of claim 5 wherein the converter has a thickness of between 100 μm and 250 μm.
9. The wavelength converter of claim 2 wherein the alumina crystallites range in size from about 0.5 μm to about 25 μm.
10. The wavelength converter of claim 2 wherein the alumina crystallites range in size from about 1 μm to about 10 μm.
11. The wavelength converter of claim 1 wherein the alumina second phase covers between about 1 to about 50 percent of the major surface.
12. The wavelength converter of claim 1 wherein the alumina second phase covers between about 5 to about 25 percent of the major surface.
13. A light-emitting device, comprising: a light-emitting diode that emits a primary light having a first peak wavelength and a wavelength converter positioned to receive the primary light from the light-emitting diode, the wavelength converter comprising a solid monolithic piece of a luminescent ceramic material, the ceramic material comprising an alumina-based phosphor capable of converting at least a portion of the primary light into secondary light having a second peak wavelength, a bulk portion of the converter being substantially transparent, and the converter having at least one major surface with an as-sintered surface layer having an alumina second phase.
14. The light-emitting device of claim 13 wherein the converter is a flat plate and both major surfaces of the plate have the as-sintered surface layer having an alumina second phase.
15. The light-emitting device of claim 13 wherein the converter is a flat plate and has a thickness of between 20 μm and 500 μm.
16. The light-emitting device of claim 13 wherein the alumina second phase comprises alumina crystallites.
17. The light-emitting device of claim 13 wherein the alumina-based phosphor is represented by a general formula A 3 B 5 O 12 :Ce, wherein A is Y, Sc, La, Gd, Lu, or Tb and B is Al, Ga or Sc.
18. The light-emitting device of claim 13 wherein the alumina-based phosphor is selected from Y 3 Al 5 O 12 :Ce, (Y,Gd) 3 Al 5 O 12 :Ce, Tb 3 Al 5 O 12 :Ce, and Lu 3 Al 5 O 12 :Ce.
19. The light-emitting device of claim 13 wherein the alumina second phase covers between about 1 to about 50 percent of the major surface.
20. The light-emitting device of claim 13 wherein the alumina second phase covers between about 5 to about 25 percent of the major surface.
21. The light-emitting device of claim 13 wherein a thickness of the surface layer is less than about 50 μm.
22. The light-emitting device of claim 13 wherein a thickness of the surface layer is less than about 10 μm.