Luminescencs of Alkali Halide Crystals Induced by UV-Light at Low Temperature

The luminescence of pure alkali halide crystals induced by the excitation with UV-light in the fundamental absorption region at low temperature is observed in NaCl, KCl, RbCl, NaBr, KBr, RbBr and KI. In KCl, RbCl and NaBr one emission band, in NaCl, KBr and RbBr two emission bands and in KI three emission bands are induced at 11°K. All of the emission bands, except one in KI, are confirmed to arise from the self-trapped exciton, or the V k - center. The quantum efficiencies for the luminescence are estimated as small as 0.1 to 0.2 in KCl, KBr and RbCl and a little larger in the other crystals. The excitation spectra and temperature dependence of the intensity of the luminescence are measured and the results are discussed in connection with the properties of the V k - center.