Effect of alkaline earth oxides on ceramization of LaF3 in aluminosilicate glass: 19F MAS-NMR study

Local environment of fluorine atoms in the lanthanum oxyfluoride aluminosilicate glasses and glass-ceramics modified by alkaline earth oxides, i.e. MgO, CaO and BaO, was studied by solid state 19F MAS-NMR spectroscopy. The effect of the type and concentration of the modifier on the formation of crystalline LaF3 phase was determined, as a function of heat treatment conditions. In all series of glasses studied, the F–Me(n), but no Na–F species were observed. The presence of F–La,Ba(n) units, in which fluorine is coordinated both by lanthanum and barium, was detected in the Ba-glass. Supplementary XRD analysis of this series confirmed that an increase of barium contents leads to the formation of Ba0.3La0.7O0.7F1.3, instead of pure LaF3 only.

Research HighlightsThe 17F-MAS-NMR results show a strong influence of the alkaline earth ions on the position of fluorine atoms in the framework of the oxyfluoride aluminosilicate glass: ► The fluorine does not make bonds with the sodium atoms exclusively (F–Na(6)). ► The formation of separate LaF3 and alkaline earth fluorides is preferred in the glasses modified by MgO and CaO. ► Lanthanum–barium fluorides are formed in the case of BaO modifier. ► F in the Ca-glass causes an increased crystallization of alkaline earth fluorides. ► An increase of F content does not facilitate LaF3 formation for Ca-glass. ► The results should facilitate the designing of optically active glass-ceramics production.