Structure, electronic transitions, and ligand field parameters of CoO-Na2O-borate glass via different La2O3 concentrations

Here, we elaborate a borate glass system with x La2O3 2 O 3 - (79-x) B2O3 2 O 3 - 20.6 Na2O 2 O - 0.4 CoO; (x = 0, 3, 6 and 9 mol%) glass composition utilizing the melt-quenching method, and studied through density, basic physical parameters, Fourier transforms-infrared (FTIR) and optical absorption spectroscopy. Further addition of La2O3, 2 O 3 , up to 9 mol%, affords an enhancement (25 %) in the glass density, besides other structural parameters revealing the role of lanthanum ions on the glass matrix. FTIR findings revealed the essential structural groups of borate glass like trigonal BO3 3 units, tetrahedra BO4 4 units, and non-bridging oxygen atoms. Here too, a propensity towards the transformation from BO3 3 units to BO4 4 units was obtained. The optical absorption spectra revealed the existence of Co2+ 2 + in octahedral and tetrahedral coordination and the presence of Co3+ 3 + in octahedral coordination. The blue color of the present glass was attributed to the absorption band at 571.6-580.9 nm of Co2+ 2 + cation within the tetrahedral complexes. Further analysis of the ligand field parameters revealed increased values of the splitting energy parameter of Co2+ 2 + in a tetrahedral field with higher La2O3 2 O 3 doping indicating a higher interplay between Co cations and their surrounding ligands. Additionally, the other ligand field parameters described the environments around the cobalt ions such as bonding nature. Finally, the glass refractive index increased with the further addition of lanthanum oxide, enhancing the glass quality for the optical realm. These reported findings show excellent properties of glass host as a promising contender in optical applications.