Band Gap Engineering and Analysis of Structural, Morphological, Optical and Surface Chemical Properties of Cu, Ag-doped and Cu-Ag Co-doped ZnO Nanoparticles

The ZnO Nanoparticles (NPs) are synthesized through a controlled sol–gel method using a zinc nitrate precursor with Ag and Cu dopants at varying concentrations (1[Formula: see text] and 2[Formula: see text], co-doping). The structural properties of Ag, Cu-doped and undoped ZnO NPs were analyzed by X-Ray Diffraction (XRD), which confirmed the hexagonal wurtzite structure of ZnO with no significant secondary peaks, indicating successful substitutional doping of Ag and Cu into the ZnO lattice. An insignificant change in peak positions and slight variations in crystallite and nanoparticle size distributions upon doping were observed, attributed to the incorporation of Ag[Formula: see text] (1.12 Å) and Cu[Formula: see text] (0.73Å) ions, whose ionic radii differ from that of Zn[Formula: see text] (0.74 Å). The morphological characteristics of the synthesized NPs were analyzed via Field Emission Scanning Electron Microscopy (FESEM), which revealed a nonsymmetrical, quasi-spherical shape of NPs with average particle sizes in the range of 48–76 nm. As doping concentration increases, nanoparticle size decreases and surface morphology becomes highly irregular, indicating dopant-induced agglomeration and strain in the crystal lattice. Energy Dispersive X-ray spectroscopy (EDX) confirms the presence of doping elements Ag and Cu in the doped ZnO samples and reports their approximate doping concentrations. The optical properties were examined using UV–Visible spectroscopy, which showed a red shift in the absorption spectra at higher doping concentrations, suggesting a narrowing of the band gap. Band-gap analysis using the Tauc equation revealed that the direct band gap decreases from 3.27 eV (undoped ZnO) to 3.10 eV as the doping level increases.