Magnesium-induced bandgap widening in NiO: An integrated theoretical–experimental study for optoelectronic applications

This study presents a comprehensive investigation of the structural and optoelectronic properties of Mg modified NiO samples by combining experimental results and theoretical calculations. NiO thin films with variable Mg concentration have been synthesized following a low-cost and scalable route and their structural, compositional and optical properties were studied by microscopy and spectroscopy techniques. Additionally, we systematically examine NiO with varying Mg concentrations under pristine and vacancy-induced conditions by means of first principles calculations. Our findings reveal that Mg incorporation consistently widens the electronic bandgap of NiO, yielding values ranging from 4.55 eV to 4.95 eV in vacancy-free structures and from 4.02 eV to 5.02 eV in structures containing Ni vacancies. The introduction of Ni vacancies decreases the bandgap significantly by creating new states within the bandgap arising from lattice distortions and electronic disruptions. Observed bandgap trends closely adhere to Vegard’s law, with calculated bowing parameters indicating significant compositional dependence in agreement with experimental results. This thorough analysis, combining experimental and theoretical approaches, highlights how precise Mg doping and vacancy engineering strategies enable targeted tuning of NiO’s electronic properties, supporting their potential application in advanced optoelectronic devices. • Mg substitution expands the NiO lattice and progressively increases the bandgap. • Optical experiments reveal bandgap widening in Mg-doped NiO nanoparticles. • HSE06 hybrid-DFT accurately reproduces bandgap trends in pristine and defective Mg:NiO. • Mg 2+ substitution weakens AFM coupling by replacing magnetic Ni 2+ ions. • Vegard-type bowing in Ni 1-x Mg x O enables tunable bandgap engineering for deep-UV devices.