Multisite Structure of PbWO_4:Eu~(3+) Crystals Investigated by Site-Selective Laser-Excitation Spectroscopy

摘要

Defect structures of Eu3+-doped PbWO4 crystals are investigated by site-selective laser-excitation spectroscopy. The excitation spectrum of the 7F0 f 5D0 transition shows a strong dependence on Eu~(3+)-concentration in PbWO4 crystals. Only one substitution site for Eu3+ is identified in the PbWO_4:Eu~(3+) (0.01 at.%) crystal, while at least six inequivalent sites are observed in the PbWO_4:Eu~(3+) (0.05 and 0.5 at.%) crystals. The charge compensation mechanisms for the observed sites are discussed in relation with annealing effects and temperature-dependent decay curves. The dominant site for Eu~(3+) in the PbWO_4 lattice seems to be due to a formation of EuPb 3+-VPb~('') dipole by charge compensation. The minor sites for Eu~(3+) are attributable to the EuPb 3+-Oi~('') dipole, a site perturbed by EuPb 3+-VPb~('') dipole, and a clustering of Eu~(3+) in the PbWO_4 lattice. The energy transfer and site distribution of Eu~(3+) are discussed in PbWO_4:Eu~(3+) (0.01, 0.05, and 0.5 at.%).