Role of Er3+ and Bi3+ ions on thermal and optical properties of Li2B4O7 glasses: Structural correlation

Glasses with general formulae xBiCl3-(100-x)Li2B4O7 where 10 ≤ x ≤ 30 and x Er2O3-(10-x)BiCl3-90Li2B4O7, where 0.1 ≤ x ≤ 0.5 mol% have been prepared to study the effect of Er2O3/BiCl3 on their physical, thermal and optical properties. Thermal stability parameter (∆T) extracted from DSC thermograms reveals that the ∆T (>100°C) depends on Er2O3 content and the glasses are suitable for fiber drawing process. Optical properties of both the investigated glass systems exhibit composition dependent trends and the properties are critically dependent on polarizabilities and ionicity of the dopant ions. The variations observed in the physical properties of investigated glasses were correlated to the structural changes occur due to the addition of BiCl3/Er2O3. 11B MAS NMR studies reveal the opening up of a tightly bound [B4O7]2− structural units with the formation of NBOs in the network. The variation of N4 (fraction of 4-coordinated boron to the total boron content) with BiCl3/Er2O3 clearly indicates the presence of different proportion of 3- and 4-coordinated borons in the glass network.