Band gap engineering of transition metal (Ni/Co) codoped in zinc oxide (ZnO) nanoparticles

Here we report on tunable bandgap engineering of single phase (Ni/Co) codoped ZnO nanoparticles controlled by different dopant concentrations. The as-synthesized ZnO nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible near infrared spectroscopy (UV-VIS-NIR), photoluminescence (PL) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). In absorption spectra, a clear blue shift of 15 nm for the Ni/Co codoped ZnO nanoparticles was observed compared to pure ZnO nanoparticles. Moreover, it demonstrates that the value of energy bandgap changes from 3.55 eV to 3.71 eV by varying the dopant concentrations. Compared to pure ZnO nanoparticles, green emission PL peak intensity is significantly reduced in the doped ZnO nanoparticles, attributed to the significant decrease in intrinsic defects. Our results improve the understanding of optical and structural properties of Ni and Co codoped ZnO nanoparticles as these nanocrystalline structures could be potential candidates for optoelectronic devices.