Influence of cobalt ions on spectroscopic and dielectric properties of Sb2O3 doped lithium fluoroborophosphate glasses

Glasses with compositions (20-x) LiF-10 Sb₂O₃-10 B₂O₃-60 P₂O₅: x CoO (0 < x < 0.25) were synthesized by conventional rapid melt quenching method. The non-crystalline nature of the samples was confirmed by XRD analysis and the glass forming abilities were analyzed by DTA studies. The compositional dependence of various structural vibrational units was analyzed by FT-IR and Raman studies. The DTA, FT-IR and Raman studies suggested a higher degree of disorder in the glass network with increasing concentration of CoO up to 0.15 mol%. The reversal trend has been observed beyond 0.15 mol% suggesting an increasing polymerization of glass network. The optical properties of LiF-Sb₂O₃-B₂O₃-P₂O₅: CoO glasses were analyzed by optical absorption and photoluminescence studies. The observations from OA and PL spectral studies suggested that the gradual increase of octahedral Co²⁺ ions with the increase in the concentration of CoO up to 0.15 mol%. At higher concentration i.e. above 0.15 mol% of CoO, there was a reduction in the concentration of octahedral Co²⁺ ions. The electrical properties of the glass samples were studied by both DC and AC conductivity studies. The dielectric dispersion analysis was also performed on the prepared glass samples. The results of these studies indicated that there is a mixed conduction (both ionic and polaronic) and the polaron hoping seems to prevail over ionic conduction in the glasses containing CoO less than 0.15 mol%. The increasing space charge polarization is responsible for enhanced values of dielectric constant, dielectric loss and AC conductivity for all frequency and temperature ranges with the increase in concentration of CoO up to 0.15 mol%.