On the local structure of Eu3+ ions in oxyfluoride glasses. Comparison with fluoride and oxide glasses

Broadband and fluorescence line narrowing optical spectroscopic studies have been used to investigate the local environments of Eu3+ ions in lithium fluoroborate glasses. From the vibronic spectra, different borate groups coupled with the Eu3+ ions have been identified. A pulsed tunable dye laser has been used to selectively excite the D05 level of the Eu3+ ion and the subsequent D05→F17 fluorescence spectra have been monitored as a function of the exciting wavelength. From these FLN studies, three F17 Stark levels have been identified and a C2v orthorhombic symmetry has been assumed in the subsequent calculation of the crystal-field parameters for the different environments occupied by the Eu3+ ions in the glass. The second rank crystal-field parameters have been systematically analyzed for the Eu3+:lithium fluoroborate glass from the site dependent behavior of the F17 level splitting. The importance of the J-mixing in the crystal-field analysis has been emphasized. An appropriate method for comparing the crystal-field interactions in different glasses has been proposed by analyzing the F17 level. Thus, results obtained for the Eu3+:fluoroborate have been compared with recalculated results in other Eu3+ doped fluoride, borate, silicate, and borosilicate glasses. An intermediate behavior between Eu3+:oxide and Eu3+:fluoride glasses is observed for the local structure of the Eu3+ ions in the fluoroborate glass, indicating the active participation of fluorine ions in the immediate environments of the lanthanide ion in this glass.