19F MAS-NMR studies of strontium oxyfluoride aluminosilicate glass

Local environment of fluorine atoms in the lanthanum oxyfluoride aluminosilicate glasses and glass–ceramics modified by SrO was studied by solid state 19F MAS-NMR spectroscopy and X-ray diffraction. The effect of strontium concentration on the formation of crystalline LaF3 phase was determined, as a function of heat treatment conditions. In all glasses studied, the F–Me(n) (where Me = Sr, La), but no Na–F species were observed. The presence of F–La,Sr(n) units, in which fluorine is coordinated by both lanthanum and strontium, was detected in the glass with higher content of SrO. Supplementary XRD analysis of this series confirmed that an increase of strontium contents leads to the formation of Sr0.69La0.31F2.31 and LaSr2F7, instead of the pure LaF3 only.

► The fluorine does not make bonds with the sodium atoms in the oxyfluoride glasses modified by SrO. ► F-La,Sr(n) units, in which fluorine is coordinated by both lanthanum and strontium, was detected. ► An increase of SrO contents leads to the formation of Sr0,69La0.31F2.31 and LaSr2F7. ► The results facilitate the process of glass composition designing for optical glass-ceramics production.