Environmental impacts of La2O3 on the optical and ligand field parameters of Ni ions inside Na2O-B2O3 glass

Journal Article

2023

Published in: https://www.sciencedirect.com/science/article/abs/pii/S0925838823021941

In this work, a glass system of La2O3, NiO, and Na2O borate glass was prepared by changing the concentrations

of La2O3/B2O3 contents. Further, the internal structure, optical absorbance, and ligand field

parameters of Ni ions were studied. The internal structure was investigated using the Fourier transform

infrared technique. The optical absorbance was measured, and the optical band gaps were obtained using

Tauc’s plot. According to the internal structure studies, BO4 contents increase with increasing La2O3/B2O3

concentrations, while BO3 contents decrease. Furthermore, the brown color and the absorption band at

424–428 nm of the prepared glass samples confirm the existence of Ni2+ cations in the form of NiO4 species

and they act as glass formers. Additionally, the observed bands at 424–428, 490–500 and 798–806 nm are

associated with the spin-allowed electron transitions of Ni2+ in octahedral coordination. Furthermore, the

observed bands at 710–718 and 940–950 nm are related to the electronic transitions for Ni2+ in tetrahedral

coordination. Moreover, the positions of all absorption bands shift toward higher wavelengths (redshift)

with higher La2O3 concentrations. Additionally, the fundamental glass absorption edges move toward lower

energy values as La2O3/B2O3 contents increase, confirming the band gaps behavior. Also, with increasing

La2O3/B2O3 contents, the linear and nonlinear refractive indices increase. These behaviors were justified by

the optical basicity and the electronic polarizability increase. On the other hand, the ligand field parameters

of Ni ions; the crystal field splitting and Racah parameters (B and C), show opposite behaviors with further

La2O3 additions. In detail, the crystal field splitting shows decreasing values and Racah parameters show

increasing values. These results reflect the tendency of the bonds between the Ni cations and their surroundings

towards a higher ionic nature (lower covalent nature).