Unraveling the role of zinc complexes on indium phosphide nanocrystal chemistry

The addition of zinc complexes to the syntheses of indium phosphide nanocrystals (InP NCs) has become commonplace, due to their ability to alter and significantly improve observed optical properties. In this paper, the role of zinc complexes on the synthesis and observed properties of InP is carefully examined. Produced InP and InP:Zn²⁺ NCs are thoroughly characterized from both structural (core and surface) and optical perspectives over a wide range of Zn²⁺ compositions (0%-43% atomic content). We find no differences in the physical (NC size and polydispersity) and structural properties (crystallographic phase) of InP and InP:Zn²⁺ NCs. Optically, significant changes are observed when zinc is added to InP syntheses, including blueshifted absorption edges and maxima, increased quantum yields, and the near elimination of surface state emission. These improved optical properties result from surface passivation by zinc carboxylate moieties. Changes to the optical properties begin at zinc concentrations as low as 5%, demonstrating the high sensitivity of InP optical properties to exogenous species.