Structural characterization of Eu2O3-MgO-Na2O-Al2O3-SiO2 glasses with varying Eu2O3 content: Raman and NMR studies

Raman, 27Al and 29Si NMR spectroscopies are used to investigate the structure of [0.15Na2O-0.12MgO-0.03Al2O3-0.70SiO2](100-x): [Eu2O3]x glasses with varying Eu2O3 content (x=0, 0.73, 1.26, 3.90, 5.26 and 8.11 mol%). Spectral changes in the Raman envelope at (900-1240) cm-1 indicate that the number of SiO2 tetrahedra with more than one non-bridging O (NBO) per tetrahedron and the number of SiO2 tetrahedra with one NBO associated with Eu increase with increasing rare-earth concentration. 29Si MAS NMR spectra show a single broad peak with maxima at frequencies attributable to a predominance of Q3 species. Quantitative 27Al and 29Si NMR spectroscopies show that aluminum and Si species become less observable as Eu2O3 content increases, presumably due to interactions with paramagnetic Eu. The 27Al NMR spectra reveal the presence of only tetrahedrally coordinated Al sites, with a gradual increase in the structural disorder associated with these sites as the concentration of Eu2O3 increases. This is in agreement with the appearance of the broad Raman band at 790 cm-1 attributed to Al-O stretching vibrations with Al in fourfold coordination. 18 refs.