A. Bessiere, P. Dorenbos, C. W. E. van Eijk, K. W. Krämer, H. U. Güdel, C. de Mello Donega and A. Meijerink
Luminescence and scintillation properties of the small band gap compound LaI₃:Ce³⁺
Nucl. Instr. Methods Phys. Res. A 537, 22-26 (2005)                 

Abstract: LaI₃:Ce³⁺ has the smallest band gap in the LaX₃:Ce³⁺ (X=F, Cl, Br, I) series and hence a potentially higher scintillation yield. The luminescence properties of LaI₃:Ce were investigated by means of optical, X-ray, and g-ray excitation. Unexpectedly, the compound is a poor scintillator at room temperature but presents good scintillation properties for temperatures below 100 K where Ce³⁺ emission is observed peaking at 452 and 502 nm with a yield of 16000 photons/MeV. The drastic thermal quenching of luminescence is explained by the proximity of the Ce³⁺ lowest 5d excited state to the host conduction band. Autoionization of Ce³⁺ therefore prevents any scintillation effect at room temperature. The positions of Ce³⁺ levels relative to the host bands were estimated.