The effect of NiO on the structural and optical properties of lithium strontium borate glasses

A series of Li₂O–SrO–B₂O₃ glasses doped with NiO were used to synthesized by the conventional melt quench technique. The effects of NiO changes on the structural and optical characteristics of lithium, strontium and borate glasses (LSBNi) were investigated using characterization methods such as XRD, Raman and UV–visible. X-ray diffraction analysis confirm the amorphous character of the glass samples. Raman studies clearly revealed that the glass network comprises of metallic vibrations Ni²⁺, Sr²⁺, Li⁺ and network forming borate groups i.e., [BO₃] and [BO₄] structural units. The presence of dopant NiO caused the conversion of trigonal [BO₃] units into tetragonal [BO₄] units as a result of this structural modification in the glasses. The optical properties were measured using UV–visible spectroscopy in the range 200–800 nm at room temperature and the existence of NiO is confirmed with appearance of broad peak at 435 nm and 666 nm. Inclusion of Ni²⁺ into the glass leads to tuneable optical band gap ranging from (2.76–4.74 eV), which consequently tunes the refractive index (2.465–2.040). These results are further correlated with the Urbach energy calculations and metallization criterion of the prepared glass samples. The electronegativity and electronic polarizability values have revealed the ionic character of glass samples.