OPTICAL-ABSORPTION SPECTRA OF THE URANIUM-(4+) ION IN THE THORIUM GERMANATE MATRIX

Visible and infrared absorption measurements on the U4+ ion in tetrago nal zircon-type matrix beta-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 squar e error equal to 65 cm(-1). The free-ion parameters obtained for the m odel Hamiltonian, zeta(5f) = 1809 cm(-1), F-2 = 43065 cm(-1), F-4 = 38 977 cm(-1) and F-6 = 24391 cm(-1), as well as the corresponding crysta l-field parameters, B-0(2) = -1790 cm(-1), B-0(4) = 1200 cm(-1), B-4(4 ) = 3260 cm(-1), B-0(6) = -3170 cm(-1) and B-4(6) = 990 cm(-1), agree fairly well with the initial theoretical estimations. The results are discussed in relation to the previous spectroscopic study on the schee lite-type matrix UGeO4.