Morphological and Photophysical Tempering in Spinel MgAl2O4 Synthesized by a Novel Citrate Route Via a Suitable Annealing Scheme

Spinel MgAl2O4 nanopowder synthesized by a novel citrate sol-gel process followed by annealing at different temperatures has been explored. Thermogravimetric and differential thermal analyses have been used to investigate the thermal qualities, and confirmed the best annealed temperature (1073 K). x-ray diffraction was used to examine the crystallinity and phase purity for the annealed samples. Fourier-transform infrared spectroscopy and electron microscopy (SEM-TEM) identified the functional groups and their morphology. The optical absorption data infer 5.12-1.8 eV band gap values (E-g) which can be significantly tailored via annealing. The thermal dependency of the emission spectra has been successfully demonstrated at two excitations, i.e. band-to-band excitation and defect-related. At 225 nm (E-g E-ex) excitation, the emissions were in the violet-blue region, while at 325 nm (Eg > E-ex) excitation, green-orange transitions dominated. The prominent emissions were further emphasized by specific color coordinates in their CIE chromaticity graphs. The annealed MgAl2O4 spinel has a higher decay constant due to an increase in radiative centers. The electronic trapping-detrapping mechanism in the overall emissions is contributed by band-to-band excitonic, shallow traps and deep states, and is also comprised of induced antisites transitions.