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.