Optical absorption spectra of the uranium (4+) ion in the thorium germanate matrix

Visible and infrared absorption measurements on the U4+ ion in tetragonal zircon-type matrix β-ThGeO4 are reported and analysed in terms of the standard parametrization scheme. The observed 17 main peaks and a number of less intense lines have been assigned and fitted to most of the 32 allowed electric dipole transitions with the root mean square error equal to 65 cm-1. The free-ion parameters obtained for the model Hamiltonian, ζ5f = 1809 cm-1, F2=43 065 cm-1, F4=38 977 cm-1 and F6=24 391 cm-1, as well as the corresponding crystal-field parameters, B02=-1790 cm-1, B04=1200 cm-1, B44=3260 cm-1, B06=-3170 cm-1 and B46=990 cm-1, agree fairly well with the initial theoretical estimations. The results are discussed in relation to the previous spectroscopic study on the scheelite-type matrix UGeO4. (author)