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

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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 (λmax≈550 nm, Φf≈0.28), a moderate CdSe→CdTe emission (λmax≈1026 nm, Φf≈1.2×10−3) and rather weak CdSe→ZnTe interband emission (λmax≈1415 nm, Φf≈1.1×10−5) 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→ZnTe (1415 nm) emission. This result further indicates an enormously long radiative lifetime of ≈10 ms. Upon excitation of the CdSe/CdTe/ZnTe structure, the long-lived charge separation may further serve as an excellent hole carrier for catalyzing the redox oxidation reaction.