Abstract
This study investigated the effects of isovalent Zr⁴⁺ and aliovalent Fe³⁺ co-doping on the structural and optical properties of SnO₂ nanoparticles synthesized by the sol-gel method. The room-temperature XRD analysis confirmed that all samples maintain a single-phase tetragonal rutile structure. Zr4+ ion was used to stabilize the identification of structurally pristine tin(IV) dioxide that inhibits grain growth. The result showed the reduction of the lattice constants. The sample's surface morphology and elemental composition were analyzed using SEM and EDX, respectively. Results revealed that the grain size decreased with the concentration of the co-dopants. XPS analysis further confirmed the Sn⁴⁺, Zr⁴⁺, and Fe³⁺ oxidation states and the formation of oxygen-vacancy-related defects. UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis shows decreasing band gap energy from 3.68 eV to 3.57 eV upon co-substitutions. The results demonstrate that Zr/Fe co-doping provides an effective route for bandgap engineering, making SnO₂ a promising material for optoelectronic, gas-sensing, and visible-light-driven photocatalytic applications.