It was recalled that intrinsic luminescence quenching of the F-center in these halides had been investigated for many years. The problem was to decide whether the non-radiative electronic transition to the ground state, after optical excitation, occurred during or after lattice relaxation in the excited electronic state. Ultra-fast time-resolved techniques showed that, in the case of NaBr, the electronic transition occurred predominantly from the relaxed excited state whereas, in NaI, the electronic transitions during and after lattice relaxation had comparable efficiencies. Another problem was whether the luminescence was quenched by aggregation of the F-center with a molecular impurity. In addition, it was desired to characterize the electronic-vibrational energy transfer, which was associated with non-radiative F-center relaxation, by measuring the population of vibrational levels after the transfer. Ultra-fast spectroscopy could contribute to a better understanding of the electronic-vibrational transfer process; especially in the case of the OH- perturbed F-center. Because of the stronger quenching of electronic luminescence, and the much faster (non-radiative) vibrational decay of OH-, much less information was currently available than in the case of CN-.

M.Leblans: Radiation Effects and Defects in Solids, 1995, 134, 39-45