Structure and optical band gap study of transparent oxyfluoride glass-ceramics containing CaF2 nanocrystals

Oxyfluoride glass-ceramics containing CaF2 nanocrystals were prepared by one-step crystallization of SiO2-Al2O3-CaO-CaF2 glasses at different temperatures. X-ray diffraction (XRD) results have revealed that CaF2 was the only precipitated crystalline phase in glass-ceramic samples. Fourier transform infrared spectroscopy (FTIR) study of the samples showed the effect of crystallization temperature on the structure. According to DTA and XRD results, suitable glass and its associated glass-ceramics were selected as the best sample in order to study the effect of crystallization on the optical properties. UV-Vis spectra of samples were recorded to determine optical properties. Fermi energy level decreased for glass-ceramics due to the increment of semiconducting behavior. Urbach energy, optical band of the specimens have been reduced by increasing of nanocrystals in glassy matrix which could be attributed to increasing of the order of the structural and formation of crystals and dangling bonds, respectively. (C) 2015 Elsevier Ltd. All rights reserved.