Origin of inhomogeneous linewidth of Eu3+ fluorescence in several oxide glasses

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Abstract
The local structure around Eu3+ ions in several oxide glasses (silicate, borate, germanate, and aluminosilicate) was investigated using both Mössbauer spectroscopy and fluorescence measurement including the fluorescence line narrowing technique. The origin of inhomogeneous broadening of fluorescence spectra is discussed. Except for silicate glasses, the isomer shift of 151Eu varied with the population of oxygen species with different microscopic optical basicity. For silicate glasses, it was found that the isomer shift and Stark splitting of 7F1 level showed no compositional dependence. It was assumed that regardless of alkali content, Eu3+ ions in silicate glasses attract a certain number of nonbridging oxygens (NBOs), which is the only species with a negative charge, when incorporated stably into a glass matrix. Further, it was generally found that larger amounts of alkali ions or smaller amounts of macroanions, such as BO4■, AlO4■, and GeO62■, bring about smaller values of inhomogeneous linewidth, ΔνIH. It was concluded that the compositional dependence of ΔνIH in oxide glasses is successfully explained from the viewpoint of the NBO‐donating ability of the glass matrix, which is related to the NBO concentration and the flexibility of the glass matrix.