Decay of exciton emission in BaFBr crystals

The decay of 4.2 and 5.15 eV exciton emission bands of BaFBr crystals was studied. The 5.15 eV decay curve is exponential at all temperatures in the range 50-100 K. Above 50 K the 5.15 eV decay time decreases in parallel to the integral intensity of this band. The 4.2 eV decay curve consists of a rise stage and decay stage. The rise lifetime decreases drastically from 200 to about 0.1 mu s in the range 60-100 K. The decay time is constant and equal to about 7 mu s. The results obtained are satisfactorily explained by a simple model with two potential minima in the triplet excited state. The potential barrier between two states derived from the temperature behaviour of the rise time is 47 meV.