Band Gap Energy of Ion‐Doped Multiferroic NaFeO2 Nanoparticles.

The band gap energy Eg of orthorhombic β‐ and hexagonal α‐NaFeO2‐bulk and nanoparticles is investigated for the first time based on a microscopic model combined with Green's function theory. Eg increases with decreasing nanoparticles size and is shape‐dependent. The competition between Coulomb and electron–phonon interactions is demonstrated. Moreover, Eg decreases with increasing Ge and Si doping concentration or increases by Mn, Cr, and Ni ion doping due to different radii of the doping and the host Fe ions, leading to varying strains. The substitution for Na ion by K or Li(Cu) ions can cause both enhancing or reducing of Eg. Thus, the band gap energy can be regulated by nanoparticles size, ion doping, electron–phonon, and Coulomb interactions. [ABSTRACT FROM AUTHOR]