Origin of TSL peaks located at 200-250 K in UV-irradiated PbWO4 crystals

Thermally stimulated luminescence (TSL) was studied for many PbWO4 crystals after their selective irradiation at 80–220 K in the 3.4–5.0 eV energy range to clarify the origin of the defects responsible for the TSL peaks located in the 200–250 K range. The conclusion is made that both in PbWO4 and PbWO4:Mo crystals the total TSL intensity and the intensity ratio of various TSL peaks are mainly determined by the concentration and type of oxygen and lead vacancies which depend on the crystal preparation and annealing conditions and on the concentration of trivalent rare-earth impurity ions. The TSL peak near 200 K is ascribed to {Pb+–WO3} centers and the peak in the 210–230 K range, to the electron centers, containing oxygen vacancies of the type of WO2 and WO. Only the 250 K peak arises from electron centers. Thermally stimulated processes are accompanied with the green G(II) emission.