Europium probe for estimation of site symmetry in glass films, glasses and crystals

The paper is devoted to the memory of Brian Wybourne the pioneer in theory of symmetry and spectra of trivalent rare earths. We evaluate here the influence of site symmetry of the surrounding molecules in glass matrices on europium ion used as a probe. A method by which systematic classification can be performed on descending site symmetry in a large number of solid hosts is based on the ratios of intensities of electric to magnetic dipole transition. Experimental work involves preparation of a number of glass matrices prepared by a sol-gel method, and incorporating trivalent europium. The fluorescence arising from the quintet D state is used to evaluate the site symmetry of the probe europium ion in the prepared matrices, crystals, conventionally prepared glasses, solutions, and complexes incorporated in sol-gel matrices. From the large amount of tabulated data one can see that for totally symmetric sites the factor I(D-0-F-2)/I(D-0-F-1) is lower than one, and increases to 10 for systems with very low symmetry sites. The absolute intensities of the transitions depend also on the amount of covalency of Eu with the surrounding ligands.