Ascendancy of Cr3+ on Cr6+ valence state and its effect on borate glass environment through CdO doping

Chromium borate glass has a stoichiometric composition of [0.3 Cr2O3-(80 - x) B2O3-19.7 Li2O-x CdO]; x = 0, 10, 20, 30, and 40 (mol. %) is amongst one of the most promising glass compositions for the optics realm being exhibits distinguishable optical transitions in both visible and ultraviolet regions. Glass materials are usually characterized by a set of experimentally techniques. Here, we exploit optical absorption, electron spin resonance, FT-IR, density, XRD, and EDX as distinct techniques to scrutinize the structural/optical properties of such glasses. Novelty, presented here, allowed to unequivocal recognize the high energy transition band of Cr6+ io similar to ns (-345 nm) by detaching this near edge optical transition that is mostly equivocal in borate glasses behind the bulk absorption edge. The amorphicity of all CdO-doped samples was scrutinized via x-ray diffraction, while the chemical composition was confirmed by EDX. The CdO doping reflects a considerable effect on the density and its related parameters. A quantitative analysis of FT-IR revealed the basic functional groups and determined both NBO and N4 ratios. These ratios related to the modifications in the essential units induced by Cd2+ ions. Alloptical spectra of CdO-doped glass samples were normalized and deconvoluted. The prevailed feature is a manifestation of high energy transition band of Cr6+, with harshly increased in the conversion from Cr6+ to Cr3+. The physical characteristics of such band (e.g., position, intensity, ..., etc) were aimly tuned through CdO doping. Other findings such as a large red shift of absorption edge (292-350 nm), narrow band gap (3.20-2.28 eV), disorderly effect (0.47-0.63 eV), and ligand field parameters (10 Dq, B, and C) were precisely determined. SlaterCondon parameters recalled the ligand field parameters to express the covalency effects. ESR data were congruous with the optical findings, manifesting the presence of resonance signals for Cr6+ and Cr3+. The present CdO-doped glasses suggest narrow band gap materials with optically active high energy transitions suitable for ultraviolet optics applications such as UV-black and white imaging, UV-forensic photography, and insect light traps.