Site-selective spectroscopy of image in bioactive glass

Europium impurity ions have been incorporated into bioactive glass hosts via a sol–gel technique. A series of the bioactive glasses was prepared by varying the calcium to silicon ratio. Trivalent europium impurities were incorporated into the hosts during the hydrolysis stage of the sol–gel process. All samples emit bright luminescence at room temperature associated with the image transitions, with 394 nm excitation. Excitation and site-selective emission studies of the europium spectra demonstrate a distinct subset of ion sites. The emission from the distinct site shows well-defined Stark levels indicating the presence of a crystalline phase. The intensity of the emission scales with the calcium content of the samples. Thus, it is demonstrated that europium luminescence can provide an optical probe of calcium crystallization, which is more sensitive than X-ray diffraction, in these technologically important glasses.