In the present study, oxyfluoride glasses containing different amounts of K2O (1.5, 3 and 4.5 weight ratio) were prepared by the convenient melting process. The network-modifying role of K2O was proved by differential thermal analysis (DTA) results, which have shown a decreasing trend of crystallization temperature in presence of more K2O. To study structural changes of samples, Fourier transfer infrared (FT-IR) spectroscopy was carried out. According to UV vis spectra, optical properties were determined. Being a glass modifier agent, K2O shortened the bond chain length and increased the transparency. Direct and indirect band gap energies were increased, which asserts the reduction of semiconducting behavior in presence of K2O. Although creation of none-bridging oxygens by adding K2O resulted in lower degree of order, the Urbach energy (0.32 eV) was still lower than other glassy systems. (C) 2015 Elsevier Ltd. All rights reserved.