LOCAL-STRUCTURE OF RARE-EARTH IONS IN FLUOROPHOSPHATE GLASSES BY PHONON SIDE-BAND AND MOSSBAUER-SPECTROSCOPY

Fluorophosphate glasses were prepared in the AlF3-AlPO4-EuF3-MF2 (M = Ca, Ba) system and the compositional dependences of Eu3+-fluorescence properties were investigated. It was found that, with an increase of AlPO4 content, the fluorescence intensities from Eu3+:5D(J) (J = 1, 2, 3) levels were decreased and the intensity ratio of (5D0 --> F-7(2))/(5D0 --> F-7(1)) was increased. The local structure and multiphonon relaxation mechanisms of Eu3+ ions were investigated by measuring the Eu-151-Mossbauer effect and phonon sideband spectra associated with the 5D2 <-- F-7(0) transition. It was concluded that the P-O- stretching mode with the highest phonon energy contributes to the rapid multiphonon relaxation of 5D(J) states and that the covalency and asymmetry of Eu3+-ligand field were increased by the addition of AlPO4 to the present glasses.