Up-conversion in elpasolite crystals doped with U3+

Two elpasolite crystals Cs2NaYBr6 and Cs2NaYCl6, both doped with U3+ were investigated. The emission from the 4G7/2,4F3/2, and 4I11/2 levels was found. Decay times of the visible emission were measured as a function of temperature. The strong influence of temperature on the decay times is discussed in terms of strong phonon coupling of the 5f3 and the 5f26d1 bands. Upon IR excitation a red emission, assigned to the 4G7/2→4I9/2 transition, was observed only in the bromide. The anti-Stokes emission is due to step by step absorption. The observed dependence of these phenomena on environment is discussed briefly.