Theoretical investigation of the luminescence centres in PbWO4 and CdWO4 crystals

Electronic structures of possible centres of luminescence in the perfect lead (PbWO4) and cadmium tungstate (CdWO4) crystals are calculated using cluster approach. Electronic states of Pb2+, and Cd2+ cations, WO42- and WO66- are obtained on the basis of partial densities of electronic states calculated for several clusters containing from 72 to 104 atoms of the crystals. Calculated energies of one-electron transitions in these centers are compared with experimental data on luminescence and luminescence excitation. Obtained results evidence in favor of a tungstate nature of intrinsic luminescence in the PbWO4 and CdWO4 crystals . I ntrinsic luminescence probably originates from the tungstate groups WO42- in scheelite-type, and from the WO66- groups in the raspite-type PbWO4 crystals. Tungstate groups WO66- are assumed to be the centres of excitation of blue-green and yellow luminescence bands in CdWO4 crystals.