Scintillation properties of pure CaF2

The temperature dependence of the decay time and scintillation light yield of pure CaF2 crystal was measured over the temperature range 8–305 K using the multiphoton coincidence counting technique. Pure CaF2 exhibits emission of triplet self-trapped excitons at 280 nm with a slow decay, the time constant of which changes significantly with temperature. The main decay time constant increases by three orders of magnitude when cooled, from 0.96±0.06 μs at 295 K to 930±40 μs at 8 K. The results obtained demonstrate that the scintillation light yield of pure CaF2 increases with decreasing temperature down to 20 K below which it is roughly constant. At low temperatures the light yield of CaF2 is estimated to be 60% relative to that of pure CaWO4. It is concluded that undoped calcium fluoride is a very attractive target material for experimental searches for rare events based on the detection of phonon and scintillation signals.