Evolution of structural and optical properties in the course of thermal evolution of sol-gel derived cobalt-doped gahnite

▶ Distribution of Co2+ ions in zinc cobalt aluminate lattice seats depend on Co loading. The green color of samples at lower temperatures is a consequence of partial oxidation of Co2+ ions and their accommodation in octahedral sites. Thermal treatment at higher temperatures promotes gradual change of color to blue, characteristic for tetrahedrally coordinated Co2+ ions. The spectra evolution could be interpreted as a progressive reduction of Co3+ to Co2+ ions at higher temperatures.