ENERGY-LEVELS AND SYMMETRY OF CE3+ IN FLUORIDE AND OXIDE CRYSTALS

Single crystal samples of Ce3+-doped fluorides [LiCaAlF6 (LiCAF), LiYF 4 (LYF), NaCaYF6 (NCYF)], and oxides [Ca2Al2SiO7 (CASM), CaYAlO4 (CYA) ] have been grown in inert and reducing atmospheres, with the intent o f studying the effects of symmetry and ligand coordination on the dopa nt energy levels. The optical absorption spectra of Ce3+ in these crys tals consist, at most, of five overlapping bands. The luminescence is also a broadband due to strong electron-phonon interaction in the 5d e xcited state. The energies of the lowest absorption band and the lumin escence band decrease along the sequence LiCAF, LYF, NCYF, CASM, and C YA. This trend may be explained by the nephelauxetic effect and loweri ng symmetry of the anion-coordinate polyhedra of Ce3+ in these crystal s. The lowest energy peak in the absorption spectrum of Ce3+ observed in CASM is coincident with the third harmonic (355 nm) of a Q-switched pulsed YAG laser. (C) 1998 American Institute of Physics. [S0021-8979 (98)04522-8].