Tailoring the structural, electronic structure and optical properties of Fe: SnO₂ nanoparticles

This paper presents the electronic structure and optical behavior of Sn_1-xFe_xO₂ (0 % ≤ x ≤ 7 %) nanoparticles synthesized using co-precipitation assisted hydrothermal method. The structural properties of as-synthesized nanoparticles were examined using XRD and Raman spectroscopy. The XRD results demonstrated that all the samples are crystallized in tetragonal (rutile) crystal structure without any hint of impurity phase. The crystallite sizes measured using XRD spectra were found to vary from 7.0 to 10.0 nm. The effect of Fe doping and local defects were identified via surface-enhanced Raman spectroscopy (SERS). The local electronic structure was studied using NEXAFS at Fe L_{3, 2}, O K edges which demonstrate that Fe ions are situated at the Sn sites with Fe³⁺ (pre-dominant) and Fe²⁺ (minor) mixed valance states. The octahedral (O_h) ligand field split the Fe (3d) state into t_2g and e_g states with ∼3 eV energy splitting. The optical properties were explored by using UV–vis spectra, which reveals transparent behavior in the visible light region and good absorption in the ultraviolet range. The asymmetrical change in the bandgap energy (3.6–3.1 eV) with the variation in Fe dopant level may be due to the casual distribution of Fe ions inside the host SnO₂ crystal texture.