  The processes of hole localization in double-doped PbWO_4:Mo,La and
PbWO_4:Mo,Y single crystals have been studied by continuous wave and pulse
electron spin resonance (ESR) and thermally stimulated luminescence (TSL)
methods. We show that the holes created by the UV irradiation are preferably
trapped at lattice oxygen ions in the vicinity of perturbing defects such as
lead vacancies, impurity ions (La, Y, Mo), and other lattice imperfections.
This leads to a variety of O^- centers, which differ both by thermal stability
(from about 170 K up to 240 K) and ESR parameters. The hole centers of this
type were not observed neither in PbWO_4:Mo nor in PbWO_4:La(Y) crystals. The
recombination processes of thermally released holes with electrons stored at
different traps, including Pb^+ - WO_3 and (MoO_4)^3- centers, are
systematically studied by TSL. Thermal stability parameters are defined by ESR
and TSL techniques for different O^- type defects.
