Vol. 38, Issue 1, pp. 259-266 (2008)

Abstract

A new type of oxyfluoride glass-ceramics based on the silicate glassy matrix and the nano-phase of LaF₃ was developed for generating the up-conversion luminescence processes. In such material, the low-phonon energy crystals of LaF₃ are desirable host for the rare-earth elements. The effect of admixture of 3 mol% of La₂F₆ on the structural changes of glasses in the Na₂O–B₂O₃–SiO₂ system was investigated. The effect of LaF₃ additive was studied using ²⁹Si, ¹¹B, and ²³Na MAS NMR to learn more about the structural role of modifiers as well as fluorine in the glassy matrix. Glasses with compositions corresponding to different B₂O₃/Na₂O and B₂O₃/(Na₂O + 3La₂F₆) ratios in the 0.6–1.2 range were obtained by melt quenching. The ²⁹Si MAS NMR spectra indicated that the [SiO₄] units are more polymerized when the ratios and the fluorine admixture increase. The ¹¹B NMR spectra revealed the presence of both [BO₄] (Q⁴) and [BO₃] (Q³) units. The fraction of Q³ increased with the decreasing sodium content. Glasses with the LaF₃ additive showed higher BO₃/BO₄ ratios. The effect of thermal treatment for glasses with the tendency towards LaF₃ crystallization was discussed in terms of structural changes.