Effect of calcination temperature on structural and optical properties of MAl2O4 (M = Ni, Cu, Zn) aluminate spinel nanoparticles

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 °C, 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.