LAUSR

Copper-doped and copper-based colloidal semiconductor nanocrystals have attracted broad attention as phosphors in many contexts, but fundamental aspects of their electronic structures that give rise to their photoluminescence are not understood. Here, we report a detailed systematic investigation of the electronic structures of Cu+-doped ZnS, alloyed Cu–In–Zn–S, and CuInS2 nanocrystals (NCs) using density functional theory. These calculations demonstrate a continuous evolution in electronic structure from lightly doped to ternary compositions. As an impurity, Cu+ introduces isolated midgap d orbitals above the valence-band edge, with large Cu(3d)–S(3p) covalency. As the Cu+ content is increased in Cu–In–Zn–S alloys, these orbitals evolve to become the CuInS2 valence band in the ternary limit. The calculations further describe the highest occupied molecular orbital (HOMO) as localized and Cu(3d)-based for all compositions from Cu+-doped ZnS to stoichiometric CuInS2. The calculations predict that the Cu(3d)...