Study of CoO amphoteric role on the optical and structural properties in sodium borosilicate glass system

In this study, the effect of amphoteric behavior of CoO on the optical absorption shift of sodium borosilicate glasses was studied. Glasses with the composition 60 SiO 2 − 20 B 2 O 3 − 20 Na 2 O doped with CoO (0.8–2.0 wt . % ) were prepared by conventional melt-quenching method at 1500 °C for 1 h. The results suggested that CoO has amphoteric behavior in the glass network. At low and high CoO contents (0.8–0.9 and 1.5–2.0 wt%), the density decreased from 2.52 to 2.39 ³ g / cm³ and from 2.51 to 2.48 ³ g / cm³ , while the hardness decreased from 595 MPa to 563 MPa and from 598 MPa to 573 MPa, respectively. These changes were accompanied by increased asymmetric vibrations, increased Urbach energy (0.21–0.27 and 0.16–0.57 eV) and decreased Fermi energy (4.41–1.76 and 1.85–1.75 eV), indicating network depolymerization. In contrast, the CoO intermediate layers (0.9–1.5 wt%) showed increased density and hardness, decreased disorder, and higher Fermi energy, indicating partial network formation behavior. The optical response showed a decrease in visible transmission and a red-shifted absorption edge.