Effect of replacement of Bi2O3 by Li2O on structural, thermal, optical and other physical properties of zinc borate glasses

Zinc bismuth borate glasses modified by lithium oxide with composition (25-x) Bi2O3-60B(2)O(3)-15ZnOxLi(2)O, where, x = 5, 10, 15, 20 and 25 mol% have been synthesized using standard melt quenching technique. Amorphous nature of the glass samples has been ascertained by appearance of broad hump in X-ray diffraction patterns. FTIR and Raman studies advocated that glass structure is mainly built of [BO4], [BO3] and [ZnO4] structural units, however, Bi2O3 exists primarily as [BiO] octahedral units. The glass transition temperature (Tg) shows a non-linear variation with increase in Li2O content. Trend in the values of 'Tg' is in accordance with change in structure of glass matrix (i.e. fraction of [BO4] units (N-4) on addition of Li2O). The values of density (r), molar volume (Vm) and crystalline volume (Vc) are found to decrease with increase in Li2O content. The percentage value of transmittance is found to increase with increase in Li2O content. Optical band gap energy 'Eg' values has been determined from fitting of experimental data with Tauc's relation and Hydrogenic excitonic model (HEM) and are found in the range of 2.432-3.211 eV. The HEM model shows good agreement with experimentally observed data, indicates the exciton formation in studied glass system. The values of Urbach energy (DE) have been estimated by fitting of experimental data with a new empirical relation and its values are found in the range of 0.194 eV -0.294 eV. The values of metallization criterion (M) were found in the range of 0.349 -0.401, suggesting that the prepared glasses may be considered as potential candidate for non-linear optical applications. (C) 2020 Elsevier B.V. All rights reserved.