Patent Number: 056051719
Section: summary

BACKGROUND OF THE INVENTION Tritium is a beta emitter with a low energy emission spectrum. The maximum electron energy is 18.6 keV with a mean around 5.7 keV. Tritium has been employed in the past in gaseous form as the leading isotope for radioluminescent applications, such as emergency signs in aircraft and hospitals where maintenance-free/absolute reliability needs exist. These lighting devices operate by having tritium in gaseous form next to a phosphor material. The beta emission from the tritium causes optical excitation of the phosphor (such as zinc sulphide) which provides the light emission. Limitations of these technologies include the fact that the only useful beta emitters are those that can be located near a phosphor. Most of the emitted electrons will fail to reach the luminescent materials, and without proper configuring, scale-up of the intensity/power level will be prohibitive. This is a direct result of the short emitted electron range in both gaseous and condensed phase media from a low energy beta emitter, such as a tritium. The range can vary from 6 mm in air to 6 microns in water to lengths that are substantially less than these distances in solid materials. But safety and environmental reasons dictate that only the lowest energy emitters (of which tritium is a prime candidate) be considered. Another limitation is safety/environmentally related. Currently most utilization of tritium is in the gaseous form. In case of containment failure, the escape of tritiated gas into the environment is rapid and difficult to contain. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to circumvent both limitations via the covalent bonding of tritium onto the interior surfaces of porous silicon. In effect the beta emitters are located at most a few angstroms from the luminescent center, namely the silicon species. Instead of a near-surface effect, the beta emitters have now become volumetric sources that are dispersed microscopically throughout the the entire porous silicon material. Practically all the beta emitters and all the silicon materials can interact with each other to the extent that the issue of the short range of the beta particles from tritium becomes irrelevant. Intensity/power level scale-up is now proportional to the volume of the device rather than to the area as in current technologies. The fact that the tritium is now encapsulated in a solid state environment with the tritium itself in condensed matter form (as interior surface chemisorbed species) renders its escape into the environment several orders of magnitude less likely than the gas-based configurations used in current technology. Thus, the present invention of a tritiated porous silicon (TPS) material provides an optical power source whose output will scale with the volume of the device, i.e., the best scaling possible, and in an embodiment where the tritium is much better contained. In this context another object of the invention is to use TPS for a self-powered solid state light source with unique characteristics for lighting applications, such as TPS as a stand-alone optical/power source in silicon-based optoelectronic device technologies or in combination as photovoltaic devices. The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.