<p>This study focuses on the structural and optical modifications in ZnO nanoparticles upon Mg doping. The nanoparticles were synthesized through a sol-gel route using nitrate precursors, yielding polycrystalline material. The X-ray diffraction (XRD) followed by Rietveld refinement confirmed the formation of the wurtzite phase of ZnO nanoparticles without any additional impurities, suggesting successful substitution of Mg²⁺ at Zn²⁺ lattice sites. The average crystallite size, calculated using the Debye–Scherrer relation, was found in the range of ~25–40 nm and exhibited a gradual increase in the crystallite size with Mg content up to 6% doping. The decrease in particle size with increasing Mg doping was observed through field emission scanning electron microscopy (FESEM) images. Fourier transform infrared microscopy (FTIR) spectra further validated the ZnO lattice framework and indicated the preservation of tetrahedral coordination around oxygen. UV–Vis absorption studies revealed slight band gap variations, characterized by an initial blue shift upon Mg incorporation followed by a minor red shift at higher doping levels. These results demonstrate that controlled Mg substitution offers a pathway to tune the structural coherence and optical response of ZnO nanomaterials.</p>