Synergistic Band-Gap Engineering and Visible-Light Activation in Fe, La Doped ZnO Nanoparticles

Fe and La-co-doped ZnO nanoparticles were prepared by using the sol-gel method. We investigated the samples' structural, morphological, vibrational, and optical properties using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy (EDS) elemental mapping, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. Rietveld refinement of the XRD pattern confirmed the p6₃mc space group and the hexagonal wurtzite structure of the samples, with no formation of secondary phases. X-ray photoelectron spectroscopy analysis revealed that, in Fe- and La-doped ZnO, zinc exists as Zn²⁺, iron as Fe³⁺, and lanthanum as La³⁺. These substances have substantial surface oxygen defects, which account for the visible emission bands. FTIR spectra confirm the presence of a hexagonal wurtzite structure and of the chemical bonds and functional groups in the sample. UV-vis DRS spectroscopy revealed a decrease in the band gap due to Fe doping. Fe and La doping reduce the band gap of ZnO, causing a redshift that enhances interaction with visible light. This makes Fe, La-doped ZnO a potential photocatalyst. The PL spectra exhibit UV emission from excitonic recombination and visible emissions, including violet light from zinc vacancies and green light from zinc-oxygen divacancy defect transitions. The correlated color temperature values are 6425-6503 K, which closely match ideal cool white light. This makes it ideal for outdoor white LED applications due to its enhanced visual acuity and brightness.