Luminescence and photo-thermally stimulated defect-creation processes in Bi3+-doped single crystals of lead tungstate.

For the first time, photoluminescence of PbWO₄:Bi crystals with different bismuth contents is studied by the time-resolved spectroscopy methods at 4.2-300 K. Photo-thermally stimulated processes of electron and hole centers creation under selective UV irradiation of the crystal in the 3-5 eV energy range and the 4.2-200 K temperature range are clarified, and the optically created electron and hole centers are identified by the thermally stimulated luminescence and electron spin resonance methods. The 2.2 eV emission of PbWO₄:Bi crystals, excited in the Bi³⁺-related absorption band overlapped with the exciton absorption band, is shown to be of an excitonic origin and is suggested to arise from the excitons of two types localized around two different Bi³⁺-related centers. No emission, arising from the electron transitions between the energy levels of Bi³⁺ ions, is observed. Photoexcitation of PbWO₄:Bi crystals in the Bi³⁺-related absorption region results also in the creation of electron and hole centers. Three new paramagnetic centers are identified: (i) two holes trapped at two regular oxygen ions located close to a Bi³⁺ ion and a lead vacancy V_Pb (the {2O^- − Bi³⁺ − V_Pb}-type hole centers); (ii) Bi⁴⁺ centers; and (iii) the O⁻-type hole centers. The concentration of single (non-compensated) oxygen and lead vacancies as traps for electrons and holes, respectively, is found to be small. The processes resulting in the appearance of the Bi³⁺-related localized exciton emission and in the creation of Bi-related electron and hole centers are discussed. [ABSTRACT FROM AUTHOR]