Complex color centers in ultraviolet-light irradiated PbWO4 single crystal

The frequency and temperature dependence of the dielectric response in mono crystalline lead tungstate was measured before and after ultraviolet-light irradiation. Irradiated crystals, but not as-grown samples, exhibited diele ctric relaxation characteristics, its activation energy being 0.3 eV and fr equency factor, around 10(8) Hz. We trace its origin to the dipoles of comp lex color centers formed in W-O tetrahedra of the lattice. That radiation a ffects the W-O bonds were confirmed by infrared spectroscopy. On the other hand, irradiated crystals did not undergo dielectric relaxation, if they ha d 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. (C) 2 000 American Institute of Physics. [S0021- 8979(00)09711-5].