Blueing, bleaching, and blinking of single CdSe/ZnS quantum dots

Wilfried G.J.H.M. van Sark, Patrick L.T.M. Frederix, Ageeth A. Bol, Hans C. Gerritsen, Andries Meijerink

Research output: Contribution to journalArticleAcademicpeer-review

254 Citations (Scopus)

Abstract

Room temperature time-resolved luminescence measurements on single CdSe/ZnS quantum dots (QDs) are presented. Luminescence spectra were recorded over time periods of up to 30 min with a time resolution down to 6 ms. A clear 30 - 40 nm blue shift in the emission wavelength is observed for QDs in ambient air, before the luminescence stops after about 2 - 3 min due to photobleaching. The blue shift is absent in a nitrogen atmosphere and photo-bleaching occurs after much longer times, 10 - 15 min. These observations are explained by photoinduced oxidation. During illumination in the presence of oxygen the surface of CdSe is oxidized, which effectively results in shrinkage of the CdSe core diameter by almost 1 nm and, consequently, in a blue shift. This also influences the blinking behavior. The faster fading of the luminescence in air suggests that photoinduced oxidation results in the formation of nonradiative recombination centers at the CdSe/ CdSeOx interface. In a nitrogen atmosphere photoinduced oxidation is prevented by the absence of oxygen. A surprising observation is a higher initial light output for CdSe/ZnS QDs in air. We explain this higher light output by a fast reduction of the lifetime of the long-lived defect states of CdSe/ZnS QDs by oxygen.

Original languageEnglish
Pages (from-to)871-879
Number of pages9
JournalChemPhysChem
Volume3
Issue number10
DOIs
Publication statusPublished - 18 Oct 2002
Externally publishedYes

Keywords

  • Optical properties
  • Photoinduced oxidation
  • Photophysics
  • Quantum dots
  • Spectral imaging

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