Relationships between glass structure and spectroscopic properties of Eu3+ and Tb-3+ doped glasses

Fluoride phosphate and phosphate glasses were doped with Eu3+ and Tb3+ ions. The relationships between glass structure and spectroscopic properties of the doped ions were of interest to obtain informations about the local glass structure around rare earth ions. Nephelauxetic shift of Tb3+ f-->d absorption band, Eu3+ fluorescence intensity ratio of D-5(0)-->F-7(2) to D-5(0)-->F-7(1) as well as electron-phonon coupling strength and phonon energy determined from Eu3+ phonon sideband spectroscopy were studied in dependence on phosphate content of the host glasses. Tb3+ fluorescence intensity ratio of D-5(4)-->F-7(J) to D-5(3)-->F-7(J) (J = 0, 1, 2... 6) transitions is affected by Tb3+ concentration and OH content of the glasses. With increasing phosphate content of the glasses, 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, Omega(2) parameter and electron-phonon coupling strength. In fluoride phosphate glasses, the diphosphate groups dominate the spectroscopic properties of the rare earth ions. The Tb3+ fluorescence intensity ratio of D-5(4)-->F-7(J) to D-5(3)-->F-7(J) increases with increasing Tb3+ concentration and OH content, respectively, due to acceleration of cross-relaxation between Tb3+ ions and due to energy transfer from Tb3+ ions to OH groups.