Structural impact of cobalt ions on BaBiBO4 glass system by means of spectroscopic and dielectric studies

Transparent BaBiBO4:CoO glasses of composition 10BaO·20Bi2O3·(70 − x)B2O3·xCoO (wt%) where 0 ⩽ x ⩽ 2.0, were synthesized and characterized by XRD. Physical properties coupled with Spectroscopic (optical absorption, photoluminescence and FTIR spectra) and dielectric studies were carried out. The area under the absorption band corresponds to 4A2(4F) → 4T1(4F) transition of Co2+(IV) is gradually increased up to 1.5 wt% of CoO and then it is decreased at 2.0 wt% of CoO. It is also supported by decrease in Co2+ ion concentration Ni, at 2.0 wt% of CoO calculated from density values. The concentration of luminescence centers of bismuth ions [Bi2+ ions in the visible region] decreased up to 1.5 wt% of CoO and increased beyond this concentration. Further, it is also noted that at higher concentrations of dopant Co2+ ions acts as redox partner of Bi3+ and reduce it to Bi2+ state. The optical band gap energy (Eg) is found to increase than the pure with 0.5 wt% of CoO and beyond this concentration the Eg value is gradually decreased. It is due to the formation of covalent Co–O–B bonds in the glass network with tetrahedral CoO4 units. From FTIR studies, at higher concentrations due to gradual increase in CoO6 units leads to formation of BO3 and BiO6 units along with NBOs. The above results are also supported by observed decrease in dielectric constant ε′, loss tan δ and σac with the initial introduction 0.5 wt% of CoO in the glass matrix at any frequency and temperature except in the relaxation temperature region.