Type-II CdSe/CdTe/ZnTe (core-shell-shell) quantum dots with cascade band edges: The separation of electron (at CdSe) and hole (at ZnTe) by the CdTe layer

Abstract

The rational design and synthesis of CdSe/CdTe/ZnTe (core-shell-shell) type-II quantum dots are reported. Their photophysical properties are investigated via the interband CdSe -> ZnTe emission and its associated relaxation dynamics. In comparison to the strong CdSe (core only) emission (lambda(max) approximate to 550 nm, Phi(f) approximate to 0.28), a moderate CdSe -> Cd Te emission (lambda(max) approximate to 1026 nm, Phi(f) approximate to 1.2 x 10(-3)) and rather weak CdSe -> Zn Te interband emission (lambda(max) approximate to 1415 nm, Phi(f) approximate to 1.1 x 10(-5)) are resolved for the CdSe/CdTe/ ZnTe structure (3.4/1.8/1.3 nm). Capping CdSe/CdTe with ZnTe results in a distant electron-hole separation between CdSe (electron) and ZnTe (hole) via an intermediate CdTe layer In the case of the CdSe/CdTe/ ZnTe structure, a lifetime as long as 150 ns is observed for the CdSe -> Zn Te (1415 nm) emission. This result further indicates an enormously long radiative lifetime of approximate to 10 ms. Upon excitation of the CdSe/CdTe/ Zn Te structure, the long-lived charge separation may further serve as an excellent hole carrier for catalyzing the redox oxidation reaction.