CRYSTAL-FIELD ANALYSIS OF U3-SPECTRUM(LIYF4 ABSORPTION)

Absorption and emission spectra of a single crystal of U3+ in LiYF4 ar e reported at room and liquid helium temperatures. From the analysis o f the polarized absorption spectra, 40 crystal-held levels have been a ssigned. Assuming that the D-2d symmetry is a good approximation for t he S-4 point symmetry site, the electrostatic, spin-orbit, and crystal -field parameters have been obtained. A least-squares adjustment yield s a mean error of 50 cm(-1) with the following values (in cm(-1)) of t he B-q(k) parameters: B-0(2) = 420, B-0(4) = -2458, B-4(4) = -2845, B- 0(6) = 93 and B-6(6) = -3280. Using the N-v parameter, it is shown tha t the crystal-field strength for U3+ in LiYF4 is a factor of 2.4 large r than for Nd3+ in the same matrix and the U3+ ground state splitting in LiYF4 is about twice as large as that in CaF2 or SrF2.