Optimization of structural, optical, and shielding properties of Ni2⁺/Ni³⁺-doped heavy metal borate glasses via La³⁺ doping

Abstract

This study investigates the impact of structural modifications induced by rare earth ions, specifically La3+, on the ligand field, optical properties, and radiation shielding capabilities of heavy metal glasses doped with Ni2+/Ni3+ ions. FT-IR spectra and density measurements confirmed the entry of La3+ cations as network modifiers, resulting in network compressibility resulting from increased sample density as well as increased non-bridging oxygen content resulting from conversion of BO4 to BO3 units. The structural modifications in turn effectively narrowed the band gap and increased the structural disorder as inferred from the gradual increase of the Urbach energy. In addition, the increase in electronic polarization and optical basicity with La₂O₃ additions led to higher linear and nonlinear refractive indices. The optical absorption bands confirmed that Ni2⁺/Ni³⁺ ions occupied octahedral and/or tetrahedral sites, while the Ni2+ tend to occupy more octahedral sites with increasing La₂O₃ content. The crystal field strength around Ni2⁺ ions increased with increasing La³⁺ concentration, along with a decrease in the nephelauxetic ratio, indicating the covalent bonding nature of Ni2⁺ ions with neighboring ions. In addition, several radiation shielding parameters were evaluated and compared with those of common shielding materials, and it was found that samples with higher La3+ ion concentration pave the way for the possibility of obtaining low-thickness glass materials for use as highly efficient radiation shielding materials, especially in the range of energies below 1 MeV.