Study of optical band gap and FTIR spectroscopy of Li2O·Bi2O3·P2O5 glasses

Glasses having composition (25 + x)Li2O·(65 − x)P2O5·10Bi2O3 (0 ≤ x ≤ 25 mol%) were prepared by normal melt quenching technique. The optical absorption spectra of the polished samples were recorded in spectral range from 200 to 3300 nm at room temperature. The optical absorption edge (λcutoff), optical band gap (Eg) and Urbach energy (ΔE) were determined from the absorption spectra. Variation in these optical parameters has been associated with the structural changes occurring in these glasses with increase in Li2O:P2O5 ratio. Variation in density (D), molar volume (VM) and glass transition temperature (Tg) has also been correlated with structural changes in the glass samples. The FTIR spectra have been recorded in the spectral range from 400 to 1400 cm−1. The FTIR spectra show the rapid depolymerization of phosphate chains with increase in Li2O content and P–O–Bi bonds are formed.