Spectroscopic studies of Eu3+ and Dy3+ centers in ThO2

Luminescence and excitation spectra of R3+-doped thorium oxide (R3+ = Eu3+, Dy3+) are reported and analyzed. ThO2 was synthesized and grown as crystal using the flux technique. Usually, R3+ ions substitute Th4+ as a cubic sit e, but charge compensation often results in the presence of other centers. Doping concentration also has an important effect on the formation of the c rystallographic sites. Using selective dye laser excitation at 12 K and sel ection rules, site symmetries of Eu3+ and Dy3+ ions in TnO(2) are determine d and fluorescence from different centers is isolated. Results show that un der conditions investigated, Eu3+ ions have O-h, and C-3v Site symmetry in ThO2 while for Dy3+ only C-3v exists. Lifetimes were measured and discussed . A crystal-field (cf) calculation has been performed on the reduced F-7(J) basis of the ground F-7 term of the Eu3+ ion. The crystal-field parameter set is then used to calculate Dy3+ energy levels in ThO2 as a test of its c onsistency.