La3+-adjusted optical and ligand field parameters in low CoO impurities Na2O-ZnO borate glass matrix

The effect of La2O3 on the ligand field and optical properties of the current glass system was investigated. In detail, the absorption band at (493-499 nm) is ascribed to T-4(1g) (F) -> T-2(1g) (H) transition of Co2+ in octahedral symmetry. The absorption band at (574-580 nm) is ascribed to (4)A(2) (4F)-> T-4(1)(4P) transitions of Co2+ in tetrahedral symmetry. On the other hand, the electronic transition at (639-644 nm) is attributed to T-5(2g)-> E-5(g) transition of Co3+ in octahedral symmetry. Moreover, the redshift of the absorption edges reduces the optical bandgaps from 3.42 eV to 3.24 eV. Additionally, the La2O3-free glass sample exhibited a transition at similar to 230 nm in the UVC region. However, this glass sample showed an displayed transparency in the UVA and UVB regions. Furthermore, the redshift of the absorption edges resulted in the glass sample with the highest La2O3 content (i.e., 8 mol%) becoming UVA transparent while blocking UVC and UVB regions. The obtained data regarding the ligand field parameters indicate an increase in the ligand field splitting (10Dq), reflecting the increased interplay strength between Co2+ in tetrahedral symmetry and its ligands. Also, the values of the nonlinear refractive index and nonlinear optical parameters increased due to the enhancement of basicity within the glass network. These findings suggest that the glass with the greatest concentration has the potential to be utilized as an optical filter that allows UVA while blocking UVC and UVB electromagnetic waves.