In this study the synthesis of nanocrystalline pure calcium aluminate (CaAl₂O₄) powders along with its composites involving iron (Fe), nickel (Ni), copper (Cu), and zinc (Zn) ions is carried out via the sol-gel auto combustion method. The structures, chemical bonds, morphologies, particle sizes, and optical, magnetic, and fluorescence properties of the calcined powders produced were examined using 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), vibrating sample magnetometry (VSM), and photoluminescence spectroscopy (PL). The full formation of the nanocomposites Fe₂O₃/CaAl₂O₄, NiO/CaAl₂O₄, CuO/CaAl₂O₄, and ZnO/CaAl₂O₄ with no impurity phases can be observed in the XRD and FT-IR results. These modified samples exhibited superior textural qualities in comparison to pure CaAl₂O₄ according to the SEM and TEM analyses, and it was demonstrated via UV-DRS analysis that the absorption and reflection levels could be enhanced in the presence of a transition metal when compared to the ultraviolet, visible, and infrared spectra of the pure sample. The bandgap energy (E_g) values for the modified samples were in the range of 1.45 eV to 5.70 eV, whereas the value for the pure sample was 4.56 eV. The PL spectra for the pure sample revealed ultraviolet, violet, blue, green, yellow, and orange emission bands in the range of 240 nm to 600 nm, although substantial changes in the emission intensity were apparent as was the case when transition metal ions were present. The VSM results indicated that the addition of magnetic ions could enable the tuning of the calcium aluminate diamagnetism to ferromagnetism.

Keywords: CaAl₂O₄, Transition metal ions, Sol-gel auto combustion, Diethanolamine, Magnetic materials, Photoluminescence.