Spectroscopic properties of Eu3+ and Tb3+ ions for local structure investigations of fluoride phosphate and phosphate glasses

The relationships between glass structure and spectroscopic properties of the doped ions Eu3+ and Tb3+ are of interest. Eu3+ and Tb3+ ions are used as structure-sensitive ions. The Omega(t)-parameters of Eu3+ were determined from absorption and emission spectra. The lifetime of the D-5(0) state of Eu3+ was calculated from Omega(t) and compared with the experimentally determined lifetime. The electron-phonon coupling strength and phonon energy were obtained from phonon sideband spectroscopy. The f --> d absorption transition of Tb3+ was used for determination of the nephelauxetic parameter. With increasing phosphate content the covalency between rare earth ions and surrounding ligands increases due to substitution of fluoride ions by oxygen ions having higher electron polarizability. This effect leads to increasing nephelauxetic shift, Ohm(2)-parameter and electron-phonon coupling strength. In fluoride phosphate glasses, the diphosphate groups dominate the spectroscopic properties of the rare earth ions.