Tailoring the Optical Characteristics of ZnO Nanoparticles by Fe/Co Dual-Doping

The purpose of this study was to investigate the influence of dual doping with Fe and Co on the microstructural, morphological, and optical properties of ZnO nanoparticles (NPs). Zn0.97–xFe0.03CoxO (x = 0, 0.01, 0.02, and 0.03) NPs were prepared via a solid-state reaction method using high-purity ZnO, Fe, and Co NPs. This study was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-visible spectrophotometry, photoluminescence (PL), and energy-dispersive X‑ray spectroscopy (EDS). XRD analysis revealed that all samples presented a pure hexagonal wurtzite str-ucture without any trace of Fe, Co, or their oxides, indicating that the dopant ions were well-substituted Zn ions. However, some peaks appear in the spectrum of the Zn0.94Fe0.03Co0.03O sample, corresponding to the secondary spinel phases ZnCo2O4 and CoFe2O4. FE-SEM micrographs showed that all samples exhibited sphere-like particles, and their sizes, aggregation degree, and morphology were slightly influenced by the dopant content. The estimated bandgap values decreased from 3.24 eV for undoped ZnO to 3.17 eV for Zn0.95Fe0.03Co0.02O NPs and then slightly increased. Moreover, the refractive index was evaluated from the bandgap energy using Moss, Ravindra Hervé-Vandamme, and Reddy models, and then compared. The PL spectra of all samples revealed strong and sharp emission peaks in the UV region, which increased in intensity as the Co content increased.