## 3 Results and Discussion
### Structural and Thermal Characterization of Sol-Gel Materials
[26] in GCs fabricated during ceramization of precursor glasses with composition (45 SiO\({}_{2}\)-25 CaF\({}_{2}\)-20 Al\({}_{2}\)O\({}_{3}\)-10 CaO):4%EuF\({}_{3}\) (treatment conditions: 700 \({}^{\circ}\)C/4 h). In addition, to verify the quantitative distribution of chemical elements in fabricated glass-ceramics, we carried out the analysis from the selected sample area containing CaF\({}_{2}\) nanocrystal using energy dispersive X-ray spectroscopy, EDS. Generally, the content of Ca and F in CaF\({}_{2}\) nanocrystal were estimated to 5 wt.% and 6 wt.%, respectively; and the content of Si and O from silicate sol-gel matrix were estimated to 41 wt.% and 48 wt.%, respectively. Since Eu\({}^{3+}\) ions were introduced during sol-gel synthesis as a dopant, their concentration was below the quantification limit and determination their quantitative distribution between CaF\({}_{2}\) nanocrystals and a silicate host was not possible. Moreover, according to another data presented in literature, we proposed the lowest treatment temperature (350 \({}^{\circ}\)C) to the fabrication of CaF\({}_{2}\):Eu\({}^{3+}\) glass-ceramic materials (550 \({}^{\circ}\)C-570 \({}^{\circ}\)C [27], 620 \({}^{\circ}\)C-680 \({}^{\circ}\)C [28], 660 \({}^{\circ}\)C [29], 800 \({}^{\circ}\)C [30]). Nowadays, the low-temperature processes are preferable and therefore, the formation of CaF\({}_{2}\) nanocrystals at 350 \({}^{\circ}\)C seems to be highly desirable. Based on weight-loss during sol-gel transformation from initial liquid sol to xerogel and taking the results from TG/DSC analysis into account, we estimated the amount of CaF\({}_{2}\) crystal fraction in the prepared GC sample. In general, it was found that during successive evaporation of volatile components (water and organic compounds used during synthesis) and progressive polycondensation reaction of silicate network, the remaining mass of fabricated xerogel was evaluated on 16.7 wt.% of the initial sol weight. Based on the TG curve shown in Figure 1, the total weight loss during heat-treatment could be estimated to about 22.0 wt.%. The second degradation step was strictly associated with thermal decomposition of Ca(CF\({}_{3}\)COO)\({}_{2}\) and the indicated weight-loss (16.18 wt.%) should be related with evaporation of CF\({}_{3}\)CFO, CO\({}_{2}\) as well as CO. Therefore, based on above results and taking the stoichiometry of thermal degradation reaction of Ca(CF\({}_{3}\)COO)\({}_{2}\) into account, the amount of CaF\({}_{2}\) crystal fraction was estimated to about 8 wt.% (simultaneously, the estimated mass of silicate sol-gel host is about 92 wt.%). Moreover, based on performed calculations, it was assumed that thermal degradation should be complete (it should be also noted that the amount of introduced Ca(CH\({}_{3}\)COO)\({}_{2}\) salt into reaction system during sol-gel synthesis was only 2.3 wt.%). Figure 2: (**a**) X-ray diffraction (XRD) patterns for xerogel and CaF\({}_{2}\):Eu\({}^{3+}\) glass-ceramic fabricated during controlled heat-treatment at 350 \({}^{\circ}\)C. Inset shows the image of glass-ceramic (GC) sample; (**b**) transmission electron microscopy (TEM) image of CaF\({}_{2}\):Eu\({}^{3+}\) nanocrystals dispersed within amorphous sol-gel host.