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

Abstract

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+ iõ 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. All-optical 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. Slater-Condon 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.