Optical properties of ternary zinc magnesium phosphate glasses

Ternary phosphate glasses of the system (ZnO)30(MgO)x(P2O5)70−x with x ranging from 5 to 20 mol% were prepared by melt quenching technique. The optical absorption spectra of these glasses were measured at room temperature in the wavelength range between 190 and 1100 nm while the refractive index at wavelength 632.8 nm. The optical absorption indicates that the electronic transition is indirect and associated with phonon-assisted transition. From the absorption spectra, the optical energy band gap (Eopt) and Urbach energy (EU) values for all the glass samples were calculated from their ultraviolet edges. The values of Eopt is found to increase from 3.36 to 3.44 eV and values of EU decrease from 0.47 to 0.29 eV with the increase of MgO content. Variation in these optical parameters, density and molar volume is discussed and correlated with the structural changes within the glassy matrix.