Coated fluorescent substance, light emitting device comprising said substance and a method for producing said substance

1. A coated phosphor, comprising:

a powder of individual grains of a phosphor as base material, the grains being coated with a non-conductive external layer of a coating material, the phosphor being excitable by ultraviolet or visible radiation,

wherein the non-conductive external layer has an inhomogeneous thickness with a mean layer thickness of at least 20 nm and comprises a plurality of individual layers, each of the individual layers comprising the coating material and being particulate in form, the individual primary particles of the non-conductive external layer being at least 5 nm in size, and at least some of the individual primary particles of the coating material of the non-conductive external layer are lumped together to form aggregates and agglomerates thereby forming the inhomogeneous thickness of the non-conductive external layer.

2. The coated phosphor as claimed in claim 1 , wherein the phosphor of the base material is selected from the group consisting of garnets, chlorosilicates, thiogallates, and aluminates.

3. The coated phosphor as claimed in claim 1 , wherein the coating material comprises an inorganic material.

4. The coated phosphor as claimed in claim 3 , wherein the BET specific surface area of the coating material is between 30 and 500 m 2 /g.

5. The coated phosphor as claimed in claim 1 , wherein the coating material comprises a material from the group of metal oxides produced by flame hydrolysis.

6. The coated phosphor as claimed in claim 5 , wherein the mean grain size of the primary particles of the non-conductive external layer, which is to be understood as meaning the d50 value of the primary grain, is at most 30 nm.

7. The coated phosphor as claimed in claim 5 , wherein the mean grain size of the primary particles of the non-conductive external layer, which is to be understood as meaning the d50 value of the primary grain, is at most 15 nm.

8. The coated phosphor as claimed in claim 5 , wherein the metal for the metal oxides is one of the group consisting of Aerosil and Alon C.

9. The coated phosphor as claimed in claim 1 , wherein the coating material comprises a metal oxide of a metal from the group consisting of Al, Si, Ti, Zr, Y.

10. The coated phosphor as claimed in claim 1 , wherein the coating material comprises a phosphor.

11. The coated phosphor as claimed in claim 1 , wherein the mean layer thickness is between 40 and 200 nm.

12. The coated phosphor as claimed in claim 1 , wherein the coating material comprises a Y203:Eu phosphor.

13. The coated phosphor as claimed in claim 1 , wherein the entire surface of the grains of the phosphor base material is coated with the non-conductive external layer.

14. The coated phosphor as claimed in claim 1 , wherein the non-conductive external layer includes only a single coating material.

15. A process for producing a coated phosphor as claimed in claim 1 , comprising the steps of:

a) providing a phosphor powder as base material;

b) providing a metal oxide produced by flame hydrolysis as coating material; and

c) dry-mixing the two materials.

16. A light-emitting device, comprising

at least one radiation source which emits radiation in the UV region or the visible wavelength region, and

a phosphor layer which at least partially converts the radiation from the radiation source into radiation with a longer wavelength, the phosphor layer being formed from a coated phosphor as claimed in claim 1 .

17. The process as claimed in claim 15 , wherein at least some of the individual primary particles of the non-conductive external layer lump together to form aggregates and agglomerates on said base material during said step of dry-mixing.