Band gap tailoring, structural and morphological properties of Zn_0.98−xMn_0.02Cu_xO (0 ≤ x ≤ 0.05) nanopowders by sol–gel method

Zn_0.98−xMn_0.02Cu_xO (0 ≤ x ≤ 0.05) nanopowders have been synthesized by sol–gel method. The synthesized nanopowders were characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–visible spectrophotometer and Fourier transform infrared spectroscopy. The XRD measurement revealed that the prepared nanopowders have different microstructure without changing a hexagonal wurtzite structure. The calculated average crystallite size was decreased from 22.4 to 16.7 nm for Cu = 0–0.02 then gradually increased to 21.5 nm for Cu = 0.05 which were confirmed by SEM. The change in lattice parameters, shift in X-ray diffraction peaks and the change in energy gap revealed the substitution of Cu²⁺ ions into Zn–Mn–O lattice. The observed red shift of optical energy gap (E_g ≈ 0.27 eV) at lower concentrations (Cu ≤ 2 %) is explained by increasing charge carriers and Moss–Burstein effect meanwhile blue shift (E_g ≈ 0.56 eV) at higher Cu concentrations (Cu > 2 %) is explained in terms of the distortion of host lattice and generation of defects. The variation of crystallite size was discussed in terms of micro-strain.