Optical Properties and Crystallization Behavior of SiO۲-Al۲O۳-BaO-BaF۲ Glasses Containing Different Amounts of Bi۲O۳

The present study aims to investigate the optical properties and crystallization behavior of oxy-fluoride glasses with different amounts of Bi۲O۳. Glasses with compositions of ۴۵SiO۲-۱۵Al۲O۳-۲۵BaO-۱۵BaF۲-xBi۲O۳ (x=۰, ۱, ۲.۵, ۴, and ۶) (mole ratio) were prepared using melt-quenching method. Owing to the network modifying role of Bi۲O۳ and increasing number of Non-Bridging Oxygens (NBOs), the molar volume increased from ۲۷.۶۹ to ۳۱.۶۰ cm۳ and microhardness was reduced from ۷۲۰.۲۱ to ۶۱۳.۱۰ MPa. In order to study the structural changes, the FTIR spectra were recorded, and increment of NBOs by adding Bi۲O۳ as well as the presence of Bi˚ particles in the sample containing six mole ratios of Bi۲O۳ were proved. The UV-Vis transmittance spectra were employed to determine the optical properties including Fermi energy, direct and indirect optical band gaps, and Urbach energy. The Fermi energy and optical band gaps were reduced as the Bi۲O۳ content increased. The degree of structural disorderliness (Urbach energy) increased from ۰.۱۷۰ to ۰.۲۱۲ eV followed by creating more NBOs through Bi۲O۳ addition. On the basis of UV-Vis-IR transmittance results, the sample containing four mole ratios of Bi۲O۳ exhibited the highest transmittance in IR region and its IR cut-off shifted to longer wavelengths. Further, the sample with six mole ratios of Bi۲O۳ was characterized as the highest refractive index (۱.۷) among other glasses. Finally, evaluation of crystallization behavior of specimens revealed that it was impossible to prepare transparent glass ceramics containing BaF۲ nanocrystals due to the surface crystallization in these glasses.

Keywords:

Optical Glass , Oxy-Fluoride , BaF۲ , Bi۲O۳