Up-conversion in elpasolite crystals doped with U3+

Two elpasolite crystals Cs2NaYBr6 and Cs2NaYCl6, both doped with U3+ were i nvestigated. The emission from the (4)G(7/2), F-4(3/2), and I-4(11/2) level s was found. Decay times of the visible emission were measured as a functio n of temperature. The strong influence of temperature on the decay times is discussed in terms of strong phonon coupling of the 5f(3) and the 5f(2)6d( 1) bands. Upon IR excitation a red emission, assigned to the 4G(7/2) --> I- 4(9/2) transition, was observed only in the bromide. The anti-Stokes emissi on is due to step by step absorption. The observed dependence of these phen omena on environment is discussed briefly. (C) 2000 Elsevier Science B.V. A ll rights reserved.