Magnesium-alloying induced photoelectronic modulation in sol-gel-processed ZnO: Strain-mediated defect passivation and bandgap tailoring

This study systematically investigates the interdependent structural, optical, and electronic evolution of Mg-alloyed ZnO nanoparticles prepared by the sol-gel method across an alloying range of 0%–12.9%, establishing a multiscale correlation framework mediated by strain engineering. Structural analyses via XRD, XPS, and HRTEM reveal an alloying-dependent substitution-interstitial transition mechanism, where low Mg concentrations (1.7%) induce coherent lattice contraction through Zn2+ substitution that suppresses oxygen vacancy formation, while high alloying concentration (12.9%) triggers interstitial incorporation and short-range disorder (FWHM broadening Δθ = 0.28°). Complementary optical characterization demonstrates non-monotonic defect-state modulation through photoluminescence spectra and Urbach energy analysis (minimum EU = 30.3 meV at 1.7% Mg), correlating strain-mediated defect passivation with suppressed deep-trap recombination in PL decay kinetics. Band structure evolution, quantified through UPS and valence band spectroscopy, reveals Fermi level elevation and strain-dominated conduction band modulation, diverging from conventional orbital hybridization models as verified by density functional theory (DFT) calculations. Hall effect studies elucidate a strain-defect interplay in which compressive strain from substitutional Mg2+ passivates oxygen vacancies, suppressing carrier scattering to enhance mobility, while interstitial Mg generates tensile strain that reactivates defect states. Critically, the systematic correlation of these multidimensional datasets establishes a strain-alloying diagram specific to solution-processed systems, bridging atomic-scale substitution mechanisms with macroscopic optoelectronic performance and providing quantitative guidelines for precision bandgap engineering in colloidal semiconductor nanomaterials.