Spectroscopic signatures of photocharging due to hot-carrier transfer in solutions of semiconductor nanocrystals under low-intensity ultraviolet excitation

John A. McGuire, Milan Sykora, István Robel, Lazaro A. Padilha, Jin Joo, Jeffrey M. Pietryga, Victor I. Klimov

Research output: Contribution to journalArticle

78 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)6087-6097
Number of pages11
JournalACS nano
Volume4
Issue number10
DOIs
Publication statusPublished - Oct 26 2010

Keywords

  • Auger recombination
  • PbSe nanocrystals
  • carrier multiplication
  • charge separation
  • charged exciton
  • photoluminescence
  • trapping

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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