Physical and optical properties of Co2+, Ni2+ doped 20ZnO + xLi2O + (30 − x)K2O + 50B2O3 (5 ≤ x ≤ 25) glasses: Observation of mixed alkali effect

► Mixed alkali effect is observed. ► Band gap studies indicate that the glasses are structural stable. ► The glasses are observed to be partially covalent in nature.