Effect of air exposure on surface properties, electronic structure, and carrier relaxation in PbSe nanocrystals

Milan Sykora, Alexey Y. Koposov, John A. McGuire, Roland K. Schulze, Olexandr Tretiak, Jeffrey M. Pietryga, Victor I. Klimov

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177 Citations (Scopus)

Abstract

Effects of air exposure on surface properties, electronic structure, and carrier relaxation dynamics in colloidal PbSe nanocrystals (NCs) were studied using X-ray photoelectron spectroscopy, transmission electron microscopy, and steady-state and time-resolved photoluminescence (PL) spectroscopies. We show that exposure of NC hexane solutions to air under ambient conditions leads to rapid oxidation of NCs such that up to 50% of their volume is transformed into PbO, SeO2, or PbSeO3 within 24 h. The oxidation is a thermally activated process, spontaneous at room temperature. The oxidation-induced reduction in the size of the PbSe "core" increases quantum confinement, causing shifts of the PL band and the absorption onset to higher energies. The exposure of NC solutions to air also causes rapid (within minutes) quenching of PL intensity followed by slow (within hours) recovery during which the PL quantum yield can reach values exceeding those observed prior to the air exposure. The short-term PL quenching is attributed to enhanced carrier trapping induced by adsorption of oxygen onto the NC surface, while the PL recovery at longer times is predominantly due to reduction in the efficiency of the "intrinsic" nonradiative interband recombination caused by the increase of the band gap in oxidized NCs. Although the analysis of subnanosecond relaxation dynamics in air-exposed NCs is complicated by a significant enhancement in fast carrier trapping, our picosecond PL measurements suggest that air exposure likely has only a weak effect on Auger recombination and also does not significantly affect the efficiency of carrier multiplication. We also show that the effects of air exposure are partially suppressed in PbSe/CdSe core/shell structures.

Original languageEnglish
Pages (from-to)2021-2034
Number of pages14
JournalACS nano
Volume4
Issue number4
DOIs
Publication statusPublished - Apr 27 2010

Keywords

  • Auger recombination
  • Carrier multiplication
  • Multiexciton generation
  • Nanocrystals
  • PbSe
  • Photochemistry
  • Quantum dots

ASJC Scopus subject areas

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

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  • Cite this

    Sykora, M., Koposov, A. Y., McGuire, J. A., Schulze, R. K., Tretiak, O., Pietryga, J. M., & Klimov, V. I. (2010). Effect of air exposure on surface properties, electronic structure, and carrier relaxation in PbSe nanocrystals. ACS nano, 4(4), 2021-2034. https://doi.org/10.1021/nn100131w