Influence of SiO 2 on the structure and optical properties of lithium bismuth silicate glasses

Abstract

Bismuth silicate glasses containing lithium oxide with composition 20Li 2O·(80 − x)Bi 2O 3· xSiO 2 (5 ⩽ x ⩽ 70 mol%) have been prepared by melt-quench technique. Density ( D), molar volume ( V M) and glass transition temperature ( T g) 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 Bi 2O 3 and SiO 2 in the formation of glass network. The increase of SiO 2 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 Bi 2O 3/SiO 2 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 ( E g) have been determined from the cutoff wavelength of these glasses. The average electronic polarizability of oxide ion ( α o 2 - ) and the optical basicity ( Λ th) have been estimated from the calculated values of the E g and were found to be dependent directly on Bi 2O 3/SiO 2 ratio. The variation in different physical parameters such as D, V M and T g and optical parameters; viz., E g, α o 2 - , Λ th with Bi 2O 3/SiO 2 ratio have been analyzed and discussed in terms of change in the glass structure.