First-principles analysis of strain -dependent optoelectronic and magnetic properties of ZnO and Ni(II)-doped ZnO nanowires

This study investigates the optoelectronic and magnetic properties of ZnO nanowires subjected to strain using first-principles calculations. The findings reveal that the bandgap of ZnO nanowires decreases under tensile strain and initially widens under compressive strain, transitioning to an indirect bandgap beyond 6 % strain. Ni substitution is energetically most favorable at the nanowire surface, enhancing ferromagnetic interactions and resulting in a Curie temperature of 634 K, which varies with strain. Mechanical strain also affects optical properties, with compressive strain causing a blue shift and tensile strain leading to a red shift in absorption bands. Ni doping improves optical properties by introducing impurity states within the bandgap, enabling fine-tuning of these properties, especially in the visible light range. This study establishes a correlation between spin-spin interactions and optical behavior, supporting the design of spintronic devices and photovoltaic systems using Ni-doped ZnO nanowires for energy conversion and storage.