Enhancement of output of optically pumped phosphor by use of surface nanostructures

1. A phosphor element comprising:

a host material defining the shape of the phosphor element; and

one or more phosphors dispersed in the host material that emit phosphorescence in response to an optical pump beam;

wherein the phosphor element has a phosphorescence-emitting surface with surface nanostructures comprising the host material; and

wherein the surface nanostructures have a lateral dimension along the phosphorescence-emitting surface of between 50 nanometers and 2 microns inclusive wherein the lateral dimension is a statistical average spacing between adjacent surface nanostructures.

2. The phosphor element of claim 1 , wherein the surface nanostructures are tapered conical surface nanostructures, frustoconical surface nanostructures, or rounded bump surface nanostructures.

3. The phosphor element of claim 1 , wherein the surface nanostructures provide a gradual change in effective refractive index that enhances phosphorescence transmission through the phosphorescence-emitting surface.

4. The phosphor element of claim 1 , wherein the surface nanostructures are laterally periodic in two dimensions over the phosphorescence-emitting surface and the lateral dimension is the periodicity of the surface nanostructures.

5. The phosphor element of claim 1 , wherein the surface nanostructures are non-periodically distributed in two dimensions over the phosphorescence-emitting surface and the lateral dimension is the statistical average spacing between adjacent surface nanostructures.

6. The phosphor element of claim 1 , wherein the surface nanostructures have a vertical height dimension of at least 100 nanometers.

7. The phosphor element of claim 1 , wherein no anti-reflection coating is disposed on the phosphorescence-emitting surface.

8. The phosphor element of claim 1 , further comprising:

a reflective coating disposed on a back surface of the phosphor element opposite from the phosphorescence-emitting surface.

9. The phosphor element of claim 1 , wherein the host material is silicone.

10. The phosphor element of claim 1 , wherein the host material is a transparent or translucent thermoplastic resin.

11. The phosphor element of claim 1 , wherein the one or more phosphors dispersed in the host material include one or more of yttrium aluminum garnet (YAG), cerium-doped YAG (YAG:Ce), lutetium YAG (LuYAG), silicate-based phosphors, and silicon-aluminum-oxynitride (SiAlON).

12. The phosphor element of claim 6 , wherein the surface nanostructures have a vertical height dimension of between 100 nanometers and 20 microns inclusive.

13. The phosphor element of claim 6 , wherein the surface nanostructures are of uniform height and the vertical height dimension is the uniform vertical height of the surface nanostructures.

14. The phosphor element of claim 6 , wherein the surface nanostructures are of non-uniform height and the vertical height dimension is the statistical average height of the surface nanostructures.

15. A phosphor wheel device comprising:

a metal wheel having a central axis via which the metal wheel is rotatable; and

one or more phosphor elements disposed along a rim of the metal wheel and secured to the metal wheel;

wherein each phosphor element is an arc segment phosphor element or the one or more of phosphor elements consist of a single annular phosphor element; and

wherein the one or more phosphor elements comprise:

a host material defining the shape of the phosphor element; and

one or more phosphors dispersed in the host material that emit phosphorescence in response to an optical pump beam;

wherein the phosphor element has a phosphorescence-emitting surface with surface nanostructures comprising the host material, the surface nanostructures comprising the host material being of non-uniform height and having a statistical average height of at least 100 nanometers.

16. The phosphor wheel of claim 15 wherein the surface nanostructures have a lateral dimension along the phosphorescence-emitting surface of between 50 nanometers and 2 microns inclusive wherein the lateral dimension is a statistical average spacing between adjacent surface nanostructures.

17. A method of manufacturing a phosphor element comprising:

injection molding the phosphor element by injecting a host material with one or more dispersed phosphors into a mold, wherein the mold defines the shape of the injection molded phosphor element;

wherein the mold includes nano-features that define surface nanostructures on a phosphorescence-emitting surface of the injection-molded phosphor element, the nano-features having a lateral dimension along the phosphorescence-emitting surface of between 50 nanometers and 2 microns inclusive wherein the lateral dimension is a statistical average spacing between adjacent surface nanostructures.

18. A light emission method comprising:

applying a pump optical beam to a phosphor element whereby one or more phosphors dispersed in a host material of the phosphor element emit phosphorescence in response to an optical pump beam; and

transmitting the phosphorescence through a phosphorescence-emitting surface of the phosphor element; and

enhancing the transmitting using surface nanostructures comprising the host material which are disposed on the phosphorescence-emitting surface and which have a lateral dimension along the phosphorescence-emitting surface of between 50 nanometers and 2 microns inclusive wherein the lateral dimension is a statistical average spacing between adjacent surface nanostructures.

19. The light emission method of claim 18 , wherein the enhancing comprises:

providing a gradual change in effective refractive index at the phosphorescence-emitting surface that gradually changes from a refractive index of the host material to a refractive index of 1.00 over the height of the surface nanostructures.