Thermal quenching of Ce3+ emission in PrX3 (X = Cl, Br) by intervalence charge transfer

The cause of the relatively low scintillation light yield of PrBr3:Ce3+ is investigated by means of optical spectroscopy, the temperature dependence of scintillation properties and the temperature dependence of optically excited decay curves of undoped and Ce3+- doped PrCl3 and PrBr3. The integrated intensity of x- ray excited luminescence of PrBr3: 5% Ce3+ shows that the light yield at room temperature (RT) is two times less than at 80 K. The decay time of Ce3+ emission optically excited to its 5d band in PrBr3: 5% Ce3+ has a single exponential decay of 11.0 +/- 1.1 and 6.0 +/- 0.6 ns at 10 K and RT, respectively. It is proposed that Ce3+ emission is quenched by a metal-to-metal charge transfer of Ce3+ + Pr3+ -> Ce4+ + Pr2+ followed by 4f -> 4f emission of Pr3+ which is strongly concentration quenched.