Long time phosphorescence in ZnMoO4 crystals

Intense long time phosphorescence was observed in ZnMoO4 crystals at low temperatures (8 and 85 K) after X-ray excitation. The phosphorescence emission was detected over 1 h when intensity of the phosphorescence decreased by three orders of magnitude. Since the phosphorescence decay kinetic cannot be approximated by hyperbolic function a model with three types of traps (shallow, phosphorescence and deep) for free charge carriers, and one recombination center (deep trap for the charge carriers of opposite sign) was developed. Analytic solutions of kinetic equation system for the traps emptying kinetics were obtained in the framework of the model. The obtained dependence of the phosphorescence intensity on time is in a good agreement with the experimental data. A theoretical analysis (confirmed by the experimental data) shows that the kinetic of traps emptying depends on an average lifetime of charge carrier on the trap, and on the trap to the deep traps concentrations ratio.