Crystal field analysis of U3+ : LiYF4 absorption spectrum

Abstract

Absorption and emission spectra of a single crystal of U 3+ in LiYF 4 are reported at room and liquid helium temperatures. From the analysis of the polarized absorption spectra, 40 crystal-field levels have been assigned. Assuming that the D 2d symmetry is a good approximation for the S 4 point symmetry site, the electrostatic, spin-orbit, and crystal-field parameters have been obtained. A least-squares adjustment yields a mean error of 50 cm −1 with the following values (in cm −1) of the B k q parameters: B 2 0 = 420, B 4 0 = − 2458, B 4 4 = − 2845, B 6 0 = 93 and B 6 6= − 3280. Using the N v parameter, it is shown that the crystal-field strength for U 3 + in LiYF 4 is a factor of 2.4 larger than for Nd 3 + in the same matrix and the U 3 + ground state splitting in LiYF 4 is about twice as large as that in CaF 2 or SrF 2.