Enhanced UV–Visible Optical Response of Cu2⁺-Doped ZnAl₂O₄ Spinel Thin Films

Nano-porous films of AlxZnO(1-x)Cu (x =0.0, 0.15, 0.25, 1.1) were synthesized using the monoethylene glycol sol-gel process. This study widely investigates the microstructural, chemical bonding, and optical properties of Al₂ZnO₄/CuO thin films. The influence of the synthesis method, CuO doping concentration, and reduced calcination time on the crystal structure and spectroscopic properties of ZnAl₂O₄/CuO spinel films was analyzed. X-ray diffraction (XRD) confirmed the formation of a cubic spinel structure (ZnAl₂O₄) with the space group Fd-3m, exhibiting an average crystallite size of approximately 13 nm. Fourier-transform infrared (FTIR) spectroscopy revealed modifications in chemical bonding due to CuO doping, confirming the presence of Al–O, Zn–O, and Zn–O–Al bonds, with additional shifts confirming CuO incorporation. UV-visible spectroscopy indicated a decrease in transmittance and a corresponding decrease in the bandgap with increasing CuO content. XPS was used to investigate the state of the material surface and the elemental composition. These findings highlight the potential applications of ZnAl₂O₄@CuO films in optoelectronics and sensor technologies, emphasizing CuO's role as a significant dopant.