Three-pulse femtosecond spectroscopy of PbSe nanocrystals: 1S bleach nonlinearity and sub-band-edge excited-state absorption assignment

Itay Gdor, Arthur Shapiro, Chunfan Yang, Diana Yanover, Efrat Lifshitz*, Sanford Ruhman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Above band-edge photoexcitation of PbSe nanocrystals induces strong below band gap absorption as well as a multiphased buildup of bleaching in the 1Se1Shtransition. The amplitudes and kinetics of these features deviate from expectations based on biexciton shifts and state filling, which are the mechanisms usually evoked to explain them. To clarify these discrepancies, the same transitions are investigated here by double-pump-probe spectroscopy. Re-exciting in the below band gap induced absorption characteristic of hot excitons is shown to produce additional excitons with high probability. In addition, pump-probe experiments on a sample saturated with single relaxed excitons prove that the resulting 1Se1Shbleach is not linear with the number of excitons per nanocrystal. This finding holds for two samples differing significantly in size, demonstrating its generality. Analysis of the results suggests that below band edge induced absorption in hot exciton states is due to excited-state absorption and not to shifted absorption of cold carriers and that 1Se1Shbleach signals are not an accurate counter of sample excitons when their distribution includes multiexciton states.

Original languageEnglish
Pages (from-to)2138-2147
Number of pages10
JournalACS Nano
Volume9
Issue number2
DOIs
StatePublished - 24 Feb 2015

Bibliographical note

Publisher Copyright:
© 2015 American Chemical Society.

Keywords

  • exciton cooling
  • multiexciton generation
  • nanocrystals
  • quantum dots
  • ultrafast spectroscopy

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