The lifetimes of fast recombination luminescence transitions in alkali halides

Measurements have been made of the lifetimes of the fast recombination luminescence transitions in alkali halides. The luminescence was excited by 2 MeV proton pulses about 2 ns wide and the lifetimes measured by the technique of single photon counting. All alkali halides in which fast luminescence occurs have been studied at 5K and 77K. The lifetimes of the major components lie in the range 1-4 ns, and in many cases a second component with a lifetime of about 10-20 ns is evident. The temperature dependence of luminescence in NaCl, KBr and KI has been measured and is compared with the behaviour of the slow luminescence in these crystals. A new model for the electronic structure of the excited states involved in recombination luminescence is proposed and compared with the model based on the inert gas molecule.