Complex color centers in ultraviolet-light irradiated PbWO4 single crystal

Abstract

The frequency and temperature dependence of the dielectric response in monocrystalline lead tungstate was measured before and after ultraviolet-light irradiation. Irradiated crystals, but not as-grown samples, exhibited dielectric relaxation characteristics, its activation energy being 0.3 eV and frequency factor, around 108 Hz. We trace its origin to the dipoles of complex color centers formed in W–O tetrahedra of the lattice. That radiation affects the W–O bonds were confirmed by infrared spectroscopy. On the other hand, irradiated crystals did not undergo dielectric relaxation, if they had been previously annealed in oxygen at a temperature where oxygen diffuses easily, as indicated by thermogravimetry. We conclude that reducing oxygen vacancy concentration effectively enhances their radiation hardness.