Influence of inclusions of intermediate tungsten oxides on characteristics of PbWO4 scintillators

Influence of phase transitions on optical and luminescence characteristics of PbWO4 (PWO) crystals, which are utilized as scintillators in high-energy physics experiments, are studied at all stages of fabrication, including preparation of raw material, intentional doping, crystal growth, and after-growth annealing. We suggest that scintillation properties and their variations in dependence of fabrication conditions are strongly influenced by the formation of inclusions of different tungsten oxides WO3-x (0 less than or equal to x less than or equal to 1). Doping the PWO crystal with L2O3-type oxides (L = Y, La, Gd) causes replacement of the phase WO3-x by a new phase WLO, where L bounds oxygen and prevents its escape from the crystal. With these results taken into account, we reproducibly fabricate crystals with dimensions 22 x 22 x 180 rum, a quantum yield of > 8.5 phe/MeV, an inhomogeneity of quantum yield along the crystal of < 5%, and a transmission of 25%, 55%, and 70% at wavelengths 360, 420, and 600 nm, respectively. The optimized technology resulting in reproducible and stable characteristics of PWO scintillators is implemented on industrial scale at the "North Crystals" Company. (C) 2002 Elsevier Science B.V. All rights reserved.