Ultraviolet luminescence and creation of (WO4)3−-type centers under UV irradiation of PbWO4 crystals doped with trivalent rare-earth ions

Abstract

Luminescence characteristics and creation of (WO4)3− and (WO4)3−-A3+ centers were studied in PbWO4 crystals doped with trivalent rare-earth A3+ ions (A3+: La3+, Lu3+, Y3+, Ce3+, Gd3+, Eu3+) under selective irradiation in the 3.4-5.0 eV energy range at 5–80 K. Optically created centers were detected by the TSL and ESR methods. Creation spectra of the mentioned centers were measured and the activation energies needed for their creation were calculated. It was found that both the (WO4)3−and (WO4)3−-A3+ centers can be created not only in the band-to-band transitions region but also in the 3.8 ± 0.4 eV range. The activation energy for their creation at T<40 K is close to zero. Under irradiation in the energy range around 3.8 eV at T>60 K, the activation energy for (WO4)3−-A3+ centers creation varies from 10 to 25 meV, depending on the irradiation energy. A new UV emission, peaking in the 3.05–3.20 eV range, was found whose thermal quenching takes place with the same activation energy. Radiative decay of defect-related states, as well as the processes of their non-radiative decay, resulting in creation of (WO4)3−-A3+ centers and thermal quenching of the UV emission, are considered to explain the effects observed.