The cause of the relatively low scintillation light yield of PrBr 3 :Ce 3+ 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 Ce 3+ -doped PrCl 3 and PrBr 3 . The integrated intensity of x-ray excited luminescence of PrBr 3 :5% Ce 3+ shows that the light yield at room temperature (RT) is two times less than at 80 K. The decay time of Ce 3+ emission optically excited to its 5d band in PrBr 3 :5% Ce 3+ 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 Ce 3+ emission is quenched by a metal-to-metal charge transfer of Ce 3+ + Pr 3+ → Ce 4+ + Pr 2+ followed by 4f → 4f emission of Pr 3+ which is strongly concentration quenched.