Electron Paramagnetic Resonance and Optical Absorption Studies of Cu²⁺ Ion-doped ZnAlBiB Glasses

Zinc alumino bismuth borate (ZnAlBiB) glasses enriched with various concentrations of Cu²⁺ ions were investigated using electron paramagnetic resonance (EPR) and optical absorption spectroscopy. The EPR spectra of all the glasses show a characteristic resonance, confirming the presence of Cu²⁺ ions within the glass matrices. The prepared glasses contained Cu²⁺ ions arranged in an octahedral coordination with tetragonal distortion, as evidenced by the spin-Hamiltonian parameters obtained from the EPR spectrum analysis. It was observed that the g_⊥ value increased as the concentration of copper ions increased. The optical absorption spectra displayed a single broad band characteristic of Cu²⁺ ions for all the prepared samples. The molecular orbital parameters were determined by comparing the EPR and optical absorption spectral data to understand the type of bonding present in these glasses. The optical bandgap energy (E_opt) and Urbach energy (E) were calculated for all ZnAlBiB glasses at the ultraviolet edges. The optical bandgap energy decreased as the concentration of copper ions increased, while the Urbach energy increased.