Explosive taggants may result from phosphors that emit visible light under IR excitation
Upconverting phosphors developed at SRI International (Menlo Park, CA) may provide easy, low-cost tagging of explosives for counterterrorism. Each phosphor contains a rare-earth- element pair, such as ytterbium and erbium. One element absorbs photons in the low-energy infrared (IR) region and transfers that energy to the other element, which emits higher-energy photons at visible wavelengths. Various combinations of rare-earth-element pairs could provide unique spectral signatures for tracing explosives containing the taggants.
Because the phosphors emit visible light, they are easily detected by the naked eye. For low concentrations of submicrometer particles, a hand-held spectral analyzer can identify the spectral emissions. These particles are particularly useful because, unless illuminated with an IR laser, their background signature is zero. Furthermore, the phosphors are pressure and temperature insensitive, so they will hold u¥before and after an explosion. But, says SRI`s David Golden, the ultimate goal is to use the phosphors for medical diagnostics, antibodies, DNA research, and possibly biological warfare detection.