Optical bandgap tuning of cubic spinel Co3O4 by annealing temperature

The optical bandgap of cubic normal spinel cobalt cobaltite (Co3O4) nanoparticles synthesized by the precipitation route has been studied. The tuning of the optical bandgap is demonstrated by annealing temperature at 400, 600, and 800°C. X-ray diffraction (XRD) analysis of all samples of Co3O4 nanoparticles confirms the single-phase cubic structure. The optical bandgap of Co3O4 nanoparticles at different annealed temperatures was studied by UV visible diffuse reflectance spectroscopy (DRS). The optical bandgap of Co3O4 nanoparticles increased as the annealing temperature varies from 400 to 800°C. The redistribution of Cobalt metal ions among the tetrahedral and octahedral sites of spinel Co3O4 structure moderated the optical bandgap with the increasing annealing temperature. The tetrahedral and octahedral peak's intensity ratios of XRD patterns, Raman spectroscopies, and FT-IR spectroscopies reveal the shifting of Co3+ ions from tetrahedral to the octahedral site, which leads to the increased optical bandgap. [Display omitted]