Spectroscopic Signatures of Photocharging due to Hot-Carrier Transfer in Solutions of Semiconductor Nanocrystals under Low-Intensity Ultraviolet Excitation

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• 作者：John A. McGuire ; Milan Sykora ; István Robel ; Lazaro A. Padilha ; Jin Joo ; Jeffrey M. Pietryga ; Victor I. Klimov
• 刊名：ACS Nano
• 出版年：2010
• 出版时间：October 26, 2010
• 年：2010
• 卷：4
• 期：10
• 页码：6087-6097
• 全文大小：486K
• 年卷期：0
• ISSN：1936-086X

文摘

We show that excitation of solutions of well-passivated PbSe semiconductor nanocrystals (NCs) with ultraviolet (3.1 eV) photons can produce long-lived charge-separated states in which the NC core is left with a nonzero net charge. Since this process is not observed for lower-energy (1.5 eV) excitation, we ascribe it to hot-carrier transfer to some trap site outside the NC. Photocharging leads to bleaching of steady-state absorption, partial quenching of emission, and additional fast time scales in carrier dynamics due to Auger decay of charged single- and multiexciton states. The degree of photocharging, f, saturates at a level that varies from 5 to 15% depending on the sample. The buildup of the population of charged NCs is extremely slow indicating very long, tens of seconds, lifetimes of these charge-separated states. Based on these time scales and the measured onset of saturation of f at excitation rates around 0.05−1 photon per NC per ms, we determine that the probability of charging following a photon absorption event is of the order of 10⁻⁴ to 10⁻³. The results of these studies have important implications for the understanding of photophysical properties of NCs, especially in the case of time-resolved measurements of carrier multiplication.