Investigation of physical, structural, optical, and luminescence properties of nickel oxide doped alkali zinco-borate glasses

Glasses having the stoichiometry ratio [(70-x) B₂O₃-10Na₂O-20ZnO-xNiO] where 0.0 ≤ x < 0.3 mol% were synthesized using a melt quenching technique. The X-ray diffraction (XRD) technique confirmed the non-crystalline properties of the glasses. Surface morphology and elemental analysis were done by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) spectra. The glass density ranged from 2.539 to 2.597 gcm^-3 and the physical characteristics such as ion concentration, inter-ionic distance, average boron-boron distance, oxygen packing density, polaron radius, and field strength were calculated and interpreted. The deconvolution spectra of Fourier Transfer Infra-Red (FTIR) and Raman spectroscopy resulted in BO₃ unit to BO₄ unit conversion as the NiO concentration increased. The UV-Visible spectroscopy showed absorption peaks near 425 nm and 800 nm corresponding to ³A_2g (F) → ³T_1g (P)) and (³A_2g (F) → ¹E_g(³F)) transitions respectively. The direct bandgap decreased from 4.00 to 3.76 eV, but the indirect bandgap increased from 3.00 to 3.12 eV. The Urbach energy of glasses decreased from 0.56 to 0.35 with an increase in NiO concentration showing the compactness of the glass network. Furthermore, optical characteristics were determined, including the refractive index, dielectric constant, metallization criterion, electronic oxide ion polarizability, optical basicity, and numerical aperture. Photoluminescence spectra exhibit strong green and cyan emission due to d-d transitions of Ni²⁺. The CIE Chromaticity coordinates confirm that the observed green light emission from BZNNi glasses are suitable candidates for optoelectronic applications.