Luminescence Decay in NaI:Pb

The dependence of the photoluminescence spectra of NaI:Pb excited in the A absorption band region on crystal temperature and dispersion state of the impurity is studied. The luminescence decay time measurements are performed for each emission band. Two lifetime components can be resolved for the A X emission, the slow component value being temperature independent. Two life‐time components independent of the temperature are observed also for the emission band of the precipitated state. The luminescence of the precipitated state is supposed to be of excitonic type due to a new phase as a result of the aggregation of the impurity. The decrease of the lifetime values of each component towards the higher energy side of the spectrum is explained by modification of the potential energy surface of the luminescent centre by the lowering of symmetry.