Influence of MgO on structure and optical properties of alumino-lithium-phosphate glasses

• Alumino Lithium Phosphate glasses doped MgO were prepared by melting quenching method.
• The introduction of MgO results in depolymerization of the phosphate glasses confirmed via Raman spectroscopy.
• The dispersion of the glass was studied using the Wemple–DiDomenico method.
• The values of Eopt and ΔE were found to vary in a non-linear manner.

MgO doped lithium alumino phosphate glasses (PLA: P2O5+Li2O+Al2O3+MgO) were prepared by melt quenching technique. Raman spectra display three significant peaks at 698, 1164 and 1383 cm−1 attributed to: symmetric stretching vibrations of the bridging oxygen (BO) in the P–O–P chains, symmetric stretching vibrations of the PO2 groups, and the asymmetric vibrations vas(PO2) of the non-bridging oxygen (NBO) atoms, respectively. Also, the density, molar volumes and ion concentration have been discussed and correlated with the structural changes within the glassy matrix. Some optical constants such as refractive index and dispersion parameters (Eo: single-oscillator energy and Ed: dispersive energy) of the glasses were determined. Finally, the values of the optical band gap for direct and indirect allowed transitions have been determined from the absorption edge studies. It is deduced that the values of Eopt increase with increasing MgO content. It was assigned to structural changes induced from the formation of non-bridging oxygen. The Urbach energy (ΔE) was found to decrease from 0.578 to 0.339 eV with increasing MgO content from 0.5 to 2 mol.