The Crystallization Effect on the Optical Properties of Oxyfluoride Glass-Ceramics Containing CaF2 Nanocrystals Doped with Y3+ Ions

In the present study, the oxyfluoride glasses of SiO2-Al2O3-CaF2 system containing different amounts of Y3+ ions were prepared through the convenient melting method. The crystallization temperatures and size of the CaF2 nanocrystals were obtained from DTA curves and XRD patterns, respectively. As a consequence, the optimum amount of Y2O3 dopant (0.5wt%) and the suitable composition for basic glass were determined from the viewpoints of better crystallization behavior and higher transparency. The FTIR spectra approved the presence of oxyfluoride glass-ceramic structure in samples. The optical parameters (Fermi energy level, Urbach energy, direct and indirect band gaps) were calculated using UV-Vis spectra. The decreasing trend of Fermi energy level for glass-ceramic samples crystallized at higher temperatures is related to better semiconducting behavior. Urbach energy and optical band gap of the glass-ceramic samples were reduced due to the increment of the structural order and the emergence of dangling bonds, respectively.