M. D. Birowosuto, P. Dorenbos, C. W. E. van Eijk, K. W. Krämer and H. U. Güdel
Thermal quenching of Ce³⁺ emission in PrX₃ (X = Cl, Br) by intervalence charge transfer
J. Phys.: Condens. Matter 19, 256209/1-16 (2007)                 

Abstract: 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.