INFLUENCE OF Gd3+ AND Y3+-DOPING ON LOW TEMPERATURE THERMOLUMINESCENCE OF Pb WO_4

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The influence of Gd3+ and Y3+ doping on the low temperature thermoluminescence (TL) of PbWO4(PWO) is investigated. In the case of polycrystal powder, the TL above 180K is eliminated by doping Y3+ or Gd3+ ions. Meanwhile, a new TL peak at lower temperature appeare. For the PWO single crystal there are two TL peaks at about 130 and 253K, but only one single peak at about 130K for PWO:Y crystals. The common effect of doping trivalent ions is to decrease or eliminate the TL above 180K and create a new TL peak at lower temperature. It indicates that the traps responsible for TL above 180K are due to the intrinsic defects which probably are Pb3+ and O-. During the preparation of PWO, the evaporation of the PbO component is easier than that of WO3, which will lead to the deficiency of PbO. The deficiency of O ions can be compensated by annealing in air while the deficiency of Pb is permanent. Therefore in the volume surrounding the Pb vacancy, there is a lack of positive charge. So the charge deficiency in the Pb-sublattic can be most easily balanced by an increase of concentration of Pb3+ and O- Doping Gd3+ or Y3+ can decrease the concentration of Pb3+ and O-. Gd3+ or Y3+ can also play a role of electron traps, which create new TL peaks at 150 and 125K, respectively. The trap depth of Gd3+ and Y3+ are 0.32 and 0.29eV, respectively. The difference between doping Gd3+ and Y3+ can be explained by the difference between their coulomb potentials.