Role of molybdenum ions on physical, optical, electrical and vibrational studies in Er3+ co-doped TeO2–ZrO2–PbCl2 glasses

(75 − x)TeO2–15PbCl2–xMoO3–10ZrO2 doped with 5 mol% Er2O3, where x = 2.5, 5, 7.5 and 10 mol%, glasses were investigated by Raman spectroscopy, dc conductivity, optical transmittance spectra and density were measured. MoO bonds are present in the entire glass composition. The glasses contain TeO4 trigonal bipyramids, TeO3+1 polyhedra and MoO6 octahedra as basic structural units. Glasses having low MoO3 content contain MoO6 octahedra having two MoO bonds. As MoO3 content increases, the fraction of MoO bonds to Mo6+ decreases. The dc conductivity increases with increase in MoO3 content, and the activation energy decreases with increase in MoO3 content. The optical band gap (Eopt) and Urbach energy (Er) were determined from the optical transmittance spectra of the polished samples recorded in the spectral range from 190 to 1100 nm at room temperature (RT). Variation in these optical parameters has also been associated with the structural changes occurring in these glasses with increase in MoO3 content, and the present glasses behave as indirect gap semiconductors.