Band Gap Modulation as a Function of Dopant Concentration and Stacking Fault in Zinc Stannate Nanostructures

This work investigates band-gap modulation in ZnSnO3 (ZS) nanostructures as a combined function of dopant concentration and stacking-fault-related defect evolution, focusing on Ni-, Cr-, and Eu-doped systems. ZS samples were analysed across 1–9 mol% dopant levels using crystallite-size analysis together with a semi-quantitative planar-disorder parameter derived from X-ray diffraction, alongside optical band-gap estimates. With increasing dopant content, the crystallite size shows a consistent decreasing trend in all three dopant series, indicating dopant-assisted nanostructure refinement accompanied by lattice perturbation. The stacking-fault-related defect parameter exhibits an overall decreasing trend with concentration, suggesting relative modification of planar disorder under identical experimental conditions. A strong dopant-dependent band-gap response is observed: Ni doping produces a clear red shift, with Eg decreasing from 3.10 eV (1 mol%) to 2.94 eV (9 mol%), while Cr doping yields an even larger narrowing, reducing Eg from 3.18 eV to 2.98 eV. In contrast, Eu doping shows only marginal variation in Eg, remaining nearly constant (3.078-3.083 eV), indicating comparatively weaker electronic perturbation of the host lattice. Overall, the results establish a defect-coupled, composition-dependent pathway for tailoring the electronic band structure of ZS, where transition-metal dopants (Ni and Cr) effectively promote band-gap narrowing, while rare-earth incorporation (Eu) preserves the wide-band-gap character. These findings indicate potential relevance of ZS for optoelectronic and photocatalytic applications, subject to further device-level validation.