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

The mixed alkaline effect in double alkaline borate glasses MgO-BaO-B2O3 containing small proportions of copper oxide (CuO) has been studied. The glass samples are characterized by optical absorption, electron paramagnetic resonance (EPR), and Fourier transform infrared spectroscopy (FTIR). A red shift in optical absorption peaks with increasing MgO (decreasing BaO) concentration has been observed. The values of “g” tensor and hyperfine “A” tensor have shown inflections with glass composition. The number of spins (N) and paramagnetic susceptibility (χ) also exhibited mixed alkaline effect. The broadening of glass network with increase in MgO concentration is found from the FTIR spectra. Interestingly both density and molar volume have shown decreasing trend with glass composition. The optical band gaps exhibited a nonlinear compositional dependence. As expected, the glass samples possessed higher values of optical basicity (Λ), molar electronic polarizability (αm), and Urbach energy (ΔE).