Correlations between structural and scintillation characteristics of lead and cadmium tungstates

Lead and cadmium tungstate, in spite of their close chemical compositions, demonstrate quite different temperature dependencies of their scintillation and structural characteristics. Scintillation light yield (LY) and decay time of lead tungstate (PWO) decrease quickly above 200 K, whereas these scintillation parameters of cadmium tungstate (CWO) are much more stable between 77 and 300 K. On the other hand, the structural behaviour of PWO demonstrates a set of distinct indications on the existence of certain phase transformations starting at 200 K, whereas no structural instabilities in CWO are observed. Analysis of theses data enabled us to assume that the fast temperature quenching of scintillation parameters of PWO above 200 K is connected with a metastability of its tetragonal lattice appearing at this temperature. This metastability induces a new channel of non-radiative recombination of electron excitations initiating local transformations of the atomic lattice to more stable structures. So in order to increase the LY of PWO scintillations at room temperature, stabilisation of PWO crystalline structure should be arranged. Several ways of this stabilisation are discussed.