Optical properties of alkaline earth borate glasses
Borate glasses containing fixed concentrations of heavy metal oxides (MO= ZnO, PbO, TeO2, Bi2O3) and alkaline earth oxides (R= Mg, Ca, Sr, Ba) are prepared by melt quenching technique. The optical band gap values are estimated from the optical absorption spectra using absorption spectrum fitting (ASF) method. The values of electronic polarizability, optical basicity and interaction parameters of the glass were discussed. The increment of refractive index values in each series is attributed to the substitution of alkaline earth oxides of increasing mass. Optical band gap (Eopt) values decreased with the replacement of RO oxides in the glass matrix. The cut-off wavelengths have shown a red shift with composition. The decrease in optical band gap values and consequently increase in Urbach’s energies confirms more extension of the localized states within the band gap. As a result there shall be an increase in the disorder of the glass network. The variation in optical parameters is owing to substitution of RO oxides in MO-B2O3 glass network.
Keywords: alkaline earth borate glasses, optical band gap, Urbach energy, refractive index, electronic polarizability, molar refraction