The optical absorption spectra of as-grown crystals exhibited mainly a weak band which peaked at 350nm and overlapped the absorption edge of the crystal. Ultraviolet-irradiated crystals emitted a strong band which peaked at 420nm, and a broad band at 500 to 700nm; together with a decrease in the 350nm band. It was found that the 420 and 500 to 700nm bands could be reduced by re-irradiation with 411nm monochromatic light, while the 350nm band was simultaneously strengthened. It was demonstrated that the increase and/or decrease in the 420nm band and the 500 to 700nm band were caused by the creation and/or annihilation of VPb2- and VO2+, respectively. The creation and annihilation of VPb2- and VO2+ were related to the separation and recombination of the vacancy pair VPb2-– VO2+, which played an important role in the formation and transformation of light-induced color centers in the crystals.

Light-Induced Coloration and Transformation Process in PbWO4 Crystals and the Effects of the Defect Pair VPb-VO. Q.Zhang, T.Liu, J.Chen, X.Feng: Physical Review B, 2003, 68[6], 064101 (5pp)