Patent Number: 
Section: claims

1. A power source, comprising:a substrate comprising a structured surface;radioactive material disposed on the structured surface, wherein the radioactive material emits radiation particles;particle converting material disposed on at least a portion of the radioactive material, wherein the particle converting material converts one or more radiation particles emitted by the radioactive material into light;a sealing layer disposed on the structured surface such that the particle converting material and the radioactive material are hermetically sealed between the sealing layer and the structured surface; anda photovoltaic device disposed directly adjacent the structured surface of the substrate, wherein the photovoltaic device converts at least a portion of the light emitted by the particle converting material that is incident upon an input surface of the photovoltaic device into electrical energy. 2. The power source of claim 1, wherein the radioactive material comprises tritium. 3. The power source of claim 1, wherein the particle converting material comprises phosphor. 4. The power source of claim 1, wherein the particle converting material comprises quantum dots. 5. The power source of claim 1, wherein the substrate comprises glass. 6. The power source of claim 1, wherein the photovoltaic device comprises a photodiode. 7. The power source of claim 1, wherein the substrate further comprises a reflective layer disposed between the substrate and the particle converting material. 8. The power source of claim 1, wherein the substrate further comprises an anti-diffusion layer disposed between the radioactive material and the substrate. 9. The power source of claim 1, further comprising an antireflective layer disposed between the sealing layer and the input surface of the photovoltaic device. 10. The power source of claim 1, wherein the input surface of the photovoltaic device is disposed on the sealing layer. 11. The power source of claim 1, wherein the substrate comprises a first major surface and a second major surface, wherein the first major surface comprises the structured surface, the power source further comprising a reflector disposed adjacent the second major surface of the substrate such that the reflector faces the photovoltaic device. 12. The power source of claim 1, wherein the sealing layer includes one or more structures that are registered with the structured surface. 13. The power source of claim 1, wherein the structured surface has a cross-sectional shape in a plane parallel to the structured surface. 14. The power source of claim 1, wherein the structured surface has a cross-sectional shape in a plane orthogonal to the structured surface. 15. The power source of claim 1, wherein the structured surface comprises structures arranged in one or more of a periodic array on or in the structured surface, a random arrangement on or in the structured surface, or a pseudo-random arrangement on or in the structured surface. 16. The power source of claim 1, wherein the particle converting material is disposed on the at least a portion of the radioactive material in at least one pattern. 17. The power source of claim 1, wherein the sealing layer is disposed on and in contact with the particle converting material layer. 18. The power source of claim 17, wherein the sealing layer conforms to the shape of the particle converting material layer. 19. An implantable medical device comprising the power source of claim 1.