SO_4~- - SO_3~- radical pair formation in Ce doped and Ce, U co-doped K_3Na(SO_4)_2: EPM evidence and its role in TSL

摘要

TSL and EPR studies on these phosphors have shown that the defect centres are intimately related to the process of TSL in these phosphors. The release of hole/electron from defect centres at the characteristic trap site initiates the luminescence process in these materials. These aspects have been clearly demonstrated in a number of alkaline earth sulphates and mixed alkaline earth sulphates doped with actinides and lanthanides, studied in our laboratory. In all the sulphate lattices, SO_4~- centre (hole trapped at SO_4~(2-) ion) has exhibited near identical behaviour both for dose dependence and thermal ionization. This was found to be associated with the TSL peak observed around 415 K in these matrices. In this paper, we discuss the results of TSL and EPR studies on cerium doped as well as cerium and uranium co-doped K_3Na(SO_4)_2.