EFFECT OF NONSTOICHIOMETRY ON SOME PROPERTIES OF LEAD TUNGSTATE SINGLE-CRYSTALS

The effect of stoichiometric deviations on the optical absorption, gam ma rays induced absorption and thermoluminescence (TL) from PbWO4 (PWO ) single crystals has been investigated. The stoichiometric deviations are found to develop yellowish coloration in this crystal. This probl em has been overcome by purifying the starting powder for minute stoic hiometric deviations through repeated crystallisations. In the case of non-stoichiometric crystals a broad absorption over the wavelength ra nge 400-500 nm is observed. This absorption gets further enhanced when the crystal is subjected to gamma-ray irradiation. Whereas, the stoic hiometric crystals, which are colourless, are found not to develop col oration for gamma exposures as high as 10 Mrad. The presence of weak T L in both types of crystals is observed for the radiation exposures of 10 Mrad. For colourless crystals, only one TL glow peak at 170 degree s C is recorded over the temperature range 30-400 degrees C. A shift i n the glow peak temperature towards the lower temperature side is obse rved in the case of non-stoichiometric crystals. This result can be us ed to detect minute stoichiometric deviations in PWO.