Studies on the origins of the absorption spectra in PbWO4 crystal

The electronic structures and absorption spectra for both the perfect PbWO4 (PWO) crystal and the three types of PWO crystals, containing VPb2−, VO2+ and a pair of VPb2−-VO2+, respectively, have been calculated using CASTEP codes with the lattice structure optimized. The calculated absorption spectra indicate that the perfect PWO crystal does not occur absorption band in the visible and near-ultraviolet region. The absorption spectra of the PWO crystal containing VPb2− exhibit seven peaks located at 1.72 eV (720 nm), 2.16 eV (570 nm), 2.81 eV (440 nm), 3.01 eV (410 nm), 3.36 eV (365 nm), 3.70 eV (335 nm) and 4.0 eV (310 nm), respectively. The absorption spectra of the PWO crystal containing VO2+ occur two peaks located at 370 nm and 420 nm. The PWO crystal containing a pair of VPb2−-VO2+ does not occur absorption band in the visible and near-ultraviolet region. This leads to the conclusions that the 370 and 420 nm absorption bands are related to the existence of both VPb2− and VO2+ in the PWO crystal and the other absorption bands are related to the existence of the VPb2− in the PWO crystal. The existence of the pair of VPb2−-VO2+ has no visible effects on the optical properties. The calculated polarized optical properties are well consistent with the experimental results.