ON THE SULPHOXY RADICALS IN CASO4-DY, NA THERMOLUMINESCENT PHOSPHOR - ELECTRON-PARAMAGNETIC RESONANCE STUDIES

Abstract

The defect centres formed in the thermoluminescent phosphor CaSO4:Dy on additionally doping with Na+ (as a charge compensator) have been studied using the technique of electron paramagnetic resonance. The Na+ ion at the Ca2+ site is found to stabilize the observed SO4- radical. The distortion of the SO4- tetrahedron is not significant and is of a different nature from that previously reported. An important feature of the new SO4- centre is that it is characterized by an axial g-tensor with g(perpendicular-to) > g(parallel-to). The addition of Na+ to CaSO4:Dy increases the concentration of this defect centre. On the other hand, the addition of dysprosium is found to enhance the formation and stabilization of the observed SO3- centre in CaSO4. The paramagnetic and thermal properties of these defect centres are discussed in relation to the observed thermoluminescence in CaSO4:Dy,Na.