Optimization of the luminescence and structural properties of Er-doped ZnO nanostructures: effect of dopant concentration and excitation wavelength

The present study reports the effect of Er doping on the structural, morphological, and optical properties of ZnO nanostructures. ZnO: Er nanorods with different doping concentrations were successfully synthesized via a hydrothermal method. X-ray diffraction and Energy-dispersive X-ray spectroscopy analyses suggest the successful incorporation of Er into the wurtzite structure of ZnO; A secondary phase of Er2O3 appears when the Er concentration exceeds 2.5 wt%. The optical band-gap of ZnO was determined from the analysis of ultraviolet–visible spectra, and a decrease of the band gap is emphasized with increasing Er concentration. Photoluminescence spectra display a strong and broad deep-level emission band, which intensified with increasing Er concentration. The current work provides more details about the excitation wavelength effect on the luminescence of pure and Er-doped ZnO materials, finding that the visible photoluminescence emission intensity could be controlled by adjusting the Er concentration as well as the excitation wavelength; better luminescence was obtained with high Er concentration and high excitation wavelength. Moreover, the DFT calculations support the experimental results and confirm that the presence of oxygen vacancies has an effect on the structural and electronic properties of ZnO. Hence, the research findings of this work could provide an experimental and theoretical reference that may motivate future research on the study of ZnO-based optoelectronic applications.