Absorption and emission spectra of U4+ diluted in ThBr4 single crystals

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Abstract
The absorption and fluorescence spectra of U4+ diluted in single crystals of ThBr4 have been measured at room temperature (77 °K) and 4.2 °K. The crystal symmetry site of the U4+ ion is D2d. Twenty three levels have been assigned and a least‐squares fit varying nine parameters (and fixing three parameters) gave a mean energy deviation of 89 cm−1. The values of the parameters obtained from the best fit are (in cm−1) F2=43 770±797, F4=31 302 ±4 200, F6=22 248±2 425, ζ=1719±44, α=36, β=−600, γ=1000, B20=−919±85, B40=−305±70, B44=−825 ±137, B60=636±917, and B64=−1937±202. There does not appear to be a systematic correlation between the crystal field parameters obtained for U4+ in ThBr4 and those reported earlier for U4+ in UCl4 or in ZrSiO4.