Effect of fluorine on the optical properties of BaF2‐BaO‐La2O3‐B2O3 glasses prepared by containerless processing

Abstract

AbstractThe glass‐forming region of the BaO‐La2O3‐B2O3 ternary system was determined by using a containerless processing. Moreover, we prepared xBaF2‐(35‐x)BaO‐15La2O3‐50B2O3 (x = 0‐35 mol%), xBaF2‐(20‐x)BaO‐20La2O3‐60B2O3 (x = 0‐20 mol%), xBaF2‐(20‐x)BaO‐15La2O3‐65B2O3 (x = 0‐20 mol%) and xBaF2‐(20‐x)BaO‐10La2O3‐70B2O3 (x = 0‐20 mol%) novel oxyfluoride glasses. The glass transition temperature, density, refractive index, and the Abbe number of these glasses were investigated. The effects of the substitution of fluorine for oxygen on the refractive index and Abbe number were discussed on the basis of electronic polarizability and resonance wavelength of oscillator. The refractive indices decreased but Abbe number increased with increasing fluorine concentration because of the decrease in resonance wavelength of oscillator. By substituting fluorine for oxygen, we developed new optical glasses (nd = 1.68‐1.74, vd = 46‐60). The fractions of BO4 unit of oxide and oxyfluoride glasses were analyzed by the 11B NMR. The conversion between BO3 and BO4 units was observed when fluorine is added to oxide glasses because, fluorine bonds with network modifier cations and the available number of network modifiers decrease with increasing fluorine concentration. These results are helpful for designing new optical glasses that are controlled to have relatively high refractive index and lower wavelength dispersion.