I−III−VI2 semiconductor nanocrystals have been applied to a host of energy conversion devices with great success. Large scale implementation of device concepts based on these materials has, however, been somewhat stymied by the strong role of defects in determining the optoelectronic characteristics of these materials. Here we present a perspective view of the role of electronic structure and defects on the physical properties, particularly the spectroscopy, of this family of materials. Applications of these materials are further discussed in this context.

We describe the electronic structure and spectroscopic properties of CuAl x Fe1–x S2 nanocrystals and their core/shell structures. The as-synthesized CuAl x Fe1–x S2 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, CuAl x Fe1–x S2 shows photoluminescence upon making a shell of zinc sulfide, which is tunable from 400 to 1400 nm (3.1 to 0.89 eV). CuAl x Fe1–x S2/ZnS are until date the only visible-infrared tunable nanocrystal fluorophore composed entirely of earth abundant elements with atomic numbers 30 and lower.