The processes of hole localization in PbWO_4:Mo,La(Y) single crystals were investigated by electron spin resonance. It was found that the holes created by uv irradiation are trapped at the regular oxygen ions in vicinity of perturbing defects such as lead vacancies, impurity ions (La,Y), and other lattice imperfections. This leads to a variety of O~- centers which differ in both the thermal stability (from about 160 K up to 240 K) and spectroscopic parameters. The thermal release of such trapped holes and their subsequent recombination with electrons stored at different traps, including (MoO_4)~(3-) complexes, are accompanied by the appearance of the thermally stimulated luminescence peaks located at around 190 K and in the 225-250 K range.
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