Influence of SiO2 on the structure and optical properties of lithium bismuth silicate glasses

Bismuth silicate glasses containing lithium oxide with composition 20Li2O·(80 − x)Bi2O3·xSiO2 (5 ⩽ x ⩽ 70 mol%) have been prepared by melt-quench technique. Density (D), molar volume (VM) and glass transition temperature (Tg) for all the glass samples have been measured. FTIR spectroscopy has been employed to investigate the structure of these glasses in order to obtain information about the competitive role of Bi2O3 and SiO2 in the formation of glass network. The increase of SiO2 content in the glass matrix results in increasing the Si–O–Si bond angle and hence the ionicity of Si–O bond increases with decrease in Bi2O3/SiO2 ratio. The optical transmittance spectra of all the glasses have been recorded in the wavelength range 200–3300 nm. The values of optical band gap (Eg) have been determined from the cutoff wavelength of these glasses. The average electronic polarizability of oxide ion (αo2-) and the optical basicity (Λth) have been estimated from the calculated values of the Eg and were found to be dependent directly on Bi2O3/SiO2 ratio. The variation in different physical parameters such as D, VM and Tg and optical parameters; viz., Eg, αo2-, Λth with Bi2O3/SiO2 ratio have been analyzed and discussed in terms of change in the glass structure.