Electronic Structure Insights Into The Tunable Luminescence Of Cualxfe1-Xs2/Zns Nanocrystals

We describe the electronic structure and spectroscopic properties of CuAlxFe1-xS2 nanocrystals and their core/shell structures. The as-synthesized CuAlxFe1-xS2 core exhibits a tetragonal chalcopyrite structure. The core material exhibits tunable band gap that spans the entire visible to near-infrared spectrum, from 3.48 to 0.53 eV. This tunability is achieved by varying the mole fraction of aluminum and iron from 1:0 to 0:1. The band gap variation with composition deviates from Vegard's law and corresponds to a bowing coefficient of 1.59 eV. Our observations are interpreted using density functional theoretical calculations. In particular, we find that the significant bowing is well accounted for through significant localization of the Fe electronic states. Most significantly, CuAlxFe1-xS2 shows photoluminescence upon making a shell of zinc sulfide, which is tunable from 400 to 1400 nm (3.1 to 0.89 eV). CuAlxFe1-xS2/ZnS are until date the only visible-infrared tunable nanocrystal fluorophore composed entirely of earth abundant elements with atomic numbers 30 and lower.