Influence of Ni, Cu and Ag Doping on Structural Defects and Optical Band Gap of

This study investigates how Ag, Ni, and Cu dopant-induced lattice distortions govern the optical band gap behavior and associated microstructural evolution of Fe2O3 nanoparticles. Doped compositions in the 1-9 mol range were examined using PXRD-derived structural/defect parameters and UV-Vis/Tauc analysis. Pristine Fe2O3 exhibits an optical band gap of 1.75 eV with high crystallinity and nanoscale crystallite dimensions. Upon doping, distinct dopant-dependent changes in crystallite size, microstrain, and dislocation density indicate that each dopant perturbs the Fe2O3 lattice through a different distortion/defect pathway. Ni incorporation results in a pronounced band-gap narrowing (3.14 to 2.50 eV) alongside crystallite refinement and elevated defect density at higher concentrations. Cu doping also promotes band-gap reduction (3.20 to 2.86 eV), accompanied by a marked crystallite growth trend, suggesting a competing interplay between lattice distortion and grain coarsening. Conversely, Ag doping shows an overall band-gap increase (2.72 to 3.06 eV) with gradual crystallite size reduction, reflecting a different distortion-driven electronic response. Overall, the results confirm that controlled lattice distortions induced by Ag, Ni, and Cu provide a practical strategy for tuning the electronic structure of Fe2O3, offering enhanced design flexibility for optoelectronic and related functional applications.