Electronic-vibrational spectra of nonequivalent europium luminescence centers in lanthanide oxides

The authors studied the EV laser-excitation spectra of europium (Eu/sup 3 +/) in yttrium and lanthanide seisquioxides, belonging to the A and C modifications of the structure. The EV spectra belonging to two different centers in the oxides of the C modification were separated. The electronic spectra and the symmetry of one of the centers in Y/sub 2/O/sub 3/ were refined. It is demonstrated that there is a relationship between the EV spectra and the structure of luminescence centers. Qualitative estimates of the relative contributions of the motions of the oxygen and metal atoms to the vibrations of the crystal lattice are reported. The EV spectra of Eu/sup 3 +/ in oxides of the cubic modification (C/sub 2/ and C/sub i/ centers) and EV spectra of Eu/sup 3 +/ in La/sub 2/O/sub 3/ (C/sub 3v/ center) were studied and obtained for the first time. The symmetry of one of the Eu/sup 3 +/ luminescence centers in Y/sub 2/O/sub 3/ was refined.