Luminescence and photo-thermally stimulated defects creation processes in PbWO4 crystals doped with trivalent rare-earth ions

In PbWO4 crystals, doped with various trivalent rare-earth A3+ ions (A3+: La3+, Lu3+, Y3+, Ce3+, Gd3+), electron (WO4)3− and {(WO4)3−–A3+} centers can be created under UV irradiation not only in the host absorption region but also in the energy range around 3.85 eV (Böhm et al., 1999; Krasnikov et al., 2010). Under excitation in the same energy range, the UV emission peak at 3.05–3.20 eV is observed. In the present work, the origin of this emission is investigated in detail by low-temperature time-resolved luminescence methods. Photo-thermally stimulated creation of (WO4)3− and {(WO4)3−–A3+} centers is studied also in PbWO4:Mo,A3+ crystals. Various processes, which could explain both the appearance of the UV emission and the creation of the {(WO4)3−–A3+}-type centers under irradiation of PbWO4: A3+ crystals in the 3.85±0.35 eV energy range, are discussed. The radiative and non-radiative decay of the excitons localized near A3+ ions is considered as the most probable mechanism to explain the observed features.