Decay kinetics of the green emission in tungstates and molybdates

摘要

Luminescence characteristics of a number of undoped and variously doped PbWO4 crystals were studied at 0.4-400 K by the time-resolved spectroscopy and compared with those of ZnWO4, CdWO4 and PbMoO4 crystals. Two types of green emission centres are detected in PbWO4 crystals. The centres of the first type are responsible for the low-temperature 2.3-2.4 eV emission observed under excitation around 3.90-3.95 eV. The structure and parameters of their relaxed excited states were determined. It was concluded that the origin of defects responsible for the green emission of the first type could vary for different crystals. The centres of the second type with the emission around 2.5 eV appear in crystals containing oxygen vacancies after the thermal destruction of Pb+-WO3 centres at T > 180 K. Decomposition of the exciton and various defect-related states was also studied, and activation energies of this process were calculated. (C) 2004 Elsevier Ltd. All rights reserved.