An investigation of the structural-optical properties of Ni2+- bearing borate glass by Li2O addition

A simple glass system [Li2O-B2O3-NiO] was prepared via the melt-quenching method. This article attempts to outline the structural-optical relationships of Ni ions-bearing lithium borate glass. XRD confirmed the glassy nature of the samples. The increase in density confirmed the formation of a rigid network constructed by BO4 units. Infrared spectra analysis confirmed a strong structure conversion from BO3 to BO4 units, with observed mitigation in non-bridging oxygen bonds. Optical absorbance spectra were analyzed to extract optical features. Nickel ions were exploited to disclose the surrounding environment in glass. A set of optical transitions of nickel ions in octahedral forms were assigned at 1287, 815, 487 and 425 nm, which are exploited to probe ligand field effects. A decrease in splitting energy values and increased interelectronic repulsion values were obtained. This is owing to the weak intensity of the interaction of Ni ions with surrounding ligands and the localization of d-electrons, respectively. These variations led to a strong enhancement in the ionicity of bonding nature. Furthermore, the brown color of the samples confirmed the occupancy of Ni2+ in octahedral sites. Moreover, the indirect optical band gap increased due to the harsh reduction in NBO. These findings pave the way toward developing optical materials with the desired optical features.