Synthesis of CdSe/ZnSe Core/Shell and CdSe/ZnSe/ZnS\nCore/Shell/Shell Nanocrystals: Surface-Ligand Strain and CdSe–ZnSe\nLattice Strain

Abstract

Size-\nand shape-controlled CdSe/ZnSe core/shell and CdSe/ZnSe/ZnS\ncore/shell/shell nanocrystals in a zinc-blende structure with (zinc)\nalkanoates as the ligands are synthesized by managing two types of\nstrains. The surface-ligand strain, strain between the inorganic crystal\nsurface and organic ligandsplays a key role for the ZnSe epitaxy\nand can be relieved via a two-step epitaxy. Small (acetate) ligands\nare necessary for both steps and branched (2-hexyl decanoate) ligands\nare needed for growing thick (2–16 monolayers) ZnSe shells\nin step 2. The CdSe–ZnSe interface results in strong/asymmetric\ntensile strain on the inner portion (within ∼7 monolayers)\nof the ZnSe shells and weak/hydrodynamic compression strain on the\nCdSe core QDs. The CdSe–ZnSe lattice strain does not noticeably\naffect the ZnSe epitaxy but significantly alters photoluminescence\n(PL) of CdSe/ZnSe/ZnS core/shell/shell QDs. With a proper thickness\nof both ZnSe and ZnS shells, CdSe/ZnSe/ZnS core/shell/shell QDs in\na green-emitting window are synthesized with near-unity PL quantum\nyield, mono-exponential PL decay dynamics, and improved photophysical/photochemical\nstability.