In this research study, magnesium-aluminum (Mg-Al) bimetallic oxide powders are synthesized via the sol-gel auto combustion method using diethanolamine (DEA) as the fuel. In order to subsequently determine the influence of calcination temperatures upon the structure, chemical bonding, morphology, optical properties, and fluorescence properties of the as-synthesized and calcined Mg-Al bimetallic oxide powders, the researcher employed X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectroscopy (UV-DRS), and photoluminescence spectroscopy (PL), respectively. It was apparent on the basis of the XRD and FT-IR analyses that those powders undergoing calcination at temperatures of 500 ℃, 700 ℃, and 900 ℃ contained the major phase magnesium aluminate (MgAl₂O₄) spinel with trace magnesium oxide (MgO) and hydrotalcite (Mg₆Al₂(CO₃)(OH)₁₆). When the calcination temperature rose to 1100 ℃, this resulted in a single phase MgAl₂O₄ while MgO and (Mg₆Al₂(CO₃)(OH)₁₆) were no longer observed. UV-DRS analysis revealed that in optimized conditions, calcination resulted in better sample absorption and reflection levels when compared to the ultraviolet, visible, and infrared spectra observed in the case of the as-synthesized sample. The bandgap energy (E_g) for calcined samples was in the range of 2.65 eV to 5.85 eV, in contrast to the value of 4.10 eV for the as-synthesized sample. Analysis of photoluminescence showed that for the as-synthesized samples and those calcined at low temperatures, visible light was emitted only in the violet, blue, and green regions with low intensity, while for samples calcined at higher temperatures, the emissions showed greater intensity and extended to the yellow and orange regions. Multiple defect centers were found in the bandgap which can explain these findings.

NiAl₂O₄, CuAl₂O₄, and ZnAl₂O₄ aluminate spinel nanoparticles were synthesized by sol-gel auto combustion method using diethanolamine (DEA) as a fuel. The effects of calcination temperature on structure, crystallinity, morphology, and optical properties of MAl₂O₄ (M = Ni, Cu, Zn) have been investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV-DRS), and photoluminescence (PL) spectroscopy. The XRD and FT-IR results confirm the formation of single-phase spinel structure of NiAl₂O₄, CuAl₂O₄, and ZnAl₂O₄ at 1200, 1000, and 600 ℃, respectively. The direct band gap of these aluminate spinels, calculated from UV-DRS spectra using the Kubelka-Munk function, is found to increase with calcination temperature. The PL spectra demonstrate that NiAl₂O₄ gives the highest blue emission intensity, while CuAl₂O₄ and ZnAl₂O₄ exhibit a very strong violet emission. During fluorescence process, the ZnAl₂O₄ emits visible light in only violet and blue regions, while NiAl₂O₄ and CuAl₂O₄ emissions extend to the green region. It seems therefore that the transition metal type and intrinsic defects in these aluminate powders are responsible for these phenomena.