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

摘要

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 (λ_(max) ≈ 550 nm, Φ_f ≈ 0.28), a moderate CdSe→CdTe emission (λ_(max) ≈ 1026 nm, Φ_f ≈ 1.2 x 10~(-3)) and rather weak CdSe → ZnTe interband emission (λ_(max) ≈ 1415 nm, Φ_f ≈ 1.1 x10~(-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 Zn Te (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.