| Summary: | Transparent oxyfluoride glass-ceramic films and self-supported layers with composition 80SiO<sub>2</sub>-20LaF<sub>3</sub> doped with Er<sup>3+</sup> have been successfully synthesized by sol-gel process for the first time. Crack-free films and self-supported layer with a maximum thickness up to 1.4 µm were obtained after heat treatment at the low temperature of 550 °C for 1 min, resulting in a LaF<sub>3</sub> crystal fraction of 18 wt%, as confirmed by quantitative Rietveld refinement. This is the highest value reported up to now for transparent oxyfluoride glass-ceramics prepared by sol-gel. This work provides a new synthesis strategy and opens the way to a wide range of potential applications of oxyfluoride glass-ceramics. The characterization by a wide range of techniques revealed the homogeneous precipitation of LaF<sub>3</sub> nanocrystals into the glass matrix. X-ray absorption spectroscopy and electron paramagnetic resonance confirmed that the Er<sup>3+</sup> ions are preferentially embedded in the low phonon-energy LaF<sub>3</sub> nanocrystals. Moreover, photoluminescence (PL) measurements confirmed the incorporation of dopants in the LaF<sub>3</sub> nanocrystals. The effective concentration of rare-earth ions in the LaF<sub>3</sub> nanocrystals is also estimated by X-ray absorption spectroscopy.
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