At 12:00 -0600 2/23/10, Randy wrote: There are a few crystals that can double frequency (halve wavelength, thereby *increasing* the energy per photon). I think these are used in laser ranging, to bring a powerful IR laser beam up into the visible so it'll transmit better through the atmosphere. I think no phosphors can do that. They can bring frequency *down* (ie absorb an ultraviolet photon, emit 2 visible or one visible and one IR or some combination). In fact, I don't recall ever hearing of a device that can do that with non-coherent light (well, as direct conversion). The problem is trying to gather 2 low-energy photons into a single high-energy photon. That turns out to be tough to do in general. There are phosphors that can be "pumped" by blue or UV light, then stimulated to re-emit visible light when IR photons hit them. (I think the Germans made IR goggles this way in WWII.) -- - Mark 210-379-4635 ----------------------------------------------------------------------- Large Asteroids headed toward planets inhabited by beings that don't have technology adequate to stop them: Think of it as Evolution in Fast-Forward.