The glasses of the composition [xCoO–(29.5 −x)Na2O–55B2O3–15ZnO–0.5Er2O3] (where
x=0, 0.3, 0.5, 1 and 3 mol%) have been prepared using melt quenching technique. The
recorded UV/VIS/NIR absorption spectra have been studied and the resulting data was
used for the ligand feld theory analysis, from which the crystal feld energy (10Dq), Racah
parameters (B, C) and nephelauxetic ratio (β) were evaluated. The observed variations in
the band gap and Urbach energy with CoO content have been discussed in relation with the
glass structure. FT-IR spectra of the samples exhibit modes of vibration corresponding to
the stretching of BO3 and BO4 unit. From IR studies, the number of non-bridging oxygens
was increased, leading to loosen structure at higher CoO concentrations. The ESR spectra
revealed that Co2+ ions are located both in distorted tetrahedral and octahedral sites.