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The Ωt intensity parameters (t=2,4,6) of Er3+ ions in several oxide glasses and the isomer shift (IS) of 151Eu Mössbauer spectra in glasses of the same composition were determined. Among these Ωt’s, the Ω6 parameter was found to have a good relation with IS; Ω6 decreases with an increase of IS which reflects the 6s electron density of rare-earth ions. From the theoretical expression of Ωt, Ω6 is considered to be more affected by the overlap integrals of the 4f and 5d orbitals than Ω2 and Ω4, and to increase with an increase of these overlap integrals. These overlap integrals are supposed to decrease when the 6s electron density is larger, since the 6s electron density shields the 5d electron orbital.

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The fluorescence and 151Eu Mössbauer spectra have been obtained for alkali borate, alkaline earth borate and rare-earth aluminate glasses containing Eu2+ ions. The Mössbauer spectra indicate that about 70 to 80% of the europium ions are present as Eu2+ ions in the borate glasses. As for the aluminate glasses, almost all of the europium ions are present as Eu2+ ions. The fluorescence spectra due to the 4f65d1 → 4f7 transition of the Eu2+ ion have been observed under excitation with UV radiation. There exists an empirical relationship that the emission energy decreases monotonically with an increase in the theoretical optical basicity of glass, irrespective of the glass systems. This relationship is explained in terms of simple crystal field theory by assuming that the splitting of the 5d levels mainly determines the emission energy of the Eu2+ ions. This empirical relationship also indicates that Eu2+ ions are distributed rather homogeneously in the present borate and aluminate glasses.

Optical properties and structure of Er3+ doped 66.7CaO•E33.3Al2O3 glasses were investigated. Among three Judd-Ofelt intensity parameters ƒ ¶2 and ƒ ¶4