Structural and size effects on the spectroscopic and redox properties of cdse nanocrystals in solution: The role of defect states

Matteo Amelia, Stefania Impellizzeri, Simone Monaco, Ibrahim Yildiz, Serena Silvi, Francisco Raymo, Alberto Credi

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

Two series of CdSe quantum dots (QDs) with different diameters are prepared, according to frequently used protocols of the same synthetic procedure. For each sample the photophysical properties and the potentials for the first reduction and oxidation processes in organic solution are determined. The band gap obtained from electrochemical experiments is compared with that determined from the absorption and luminescence spectra. While the optical band gap decreases upon increasing the nanocrystal diameter, as expected on the basis of quantum confinement, the redox potentials and the electrochemical band gap are not monotonously related to the QD size. For both series, the smallest and largest QDs are both easier to oxidize and reduce than mid-sized QDs. In fact, the latter samples exhibit very broad voltammetric profiles, which suggests that the heterogeneous electron-transfer processes from/to the electrode are kinetically hindered. Conversely, the electrochemical band gap for the smallest and largest particles of each series is somewhat smaller than the optical band gap. These results indicate that, while the optical band gap depends on the actual electron-hole recombination within the nanocrystal, and therefore follows the size dependence expected from the particle-in-a-box model, the electrochemical processes of these QDs are strongly affected by other factors, such as the presence of surface defects. The investigations suggest that the influence of these defects on the potential values is more important for the smallest and largest QDs of each series, as confirmed by the respective luminescence bands and quantum yields. An interpretation for the size-dependent evolution of the surface defects in these nanocrystals is proposed based on the mechanism of their formation and growth.

Original languageEnglish
Pages (from-to)2280-2288
Number of pages9
JournalChemPhysChem
Volume12
Issue number12
DOIs
StatePublished - Aug 22 2011

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Nanocrystals
Semiconductor quantum dots
nanocrystals
quantum dots
Defects
Optical band gaps
defects
Energy gap
Surface defects
surface defects
Luminescence
Quantum confinement
luminescence
Electrons
Quantum yield
Oxidation-Reduction
boxes
electron transfer
Oxidation
Electrodes

Keywords

  • electrochemistry
  • electron transfer
  • luminescence
  • quantum dots
  • surface properties

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Atomic and Molecular Physics, and Optics

Cite this

Structural and size effects on the spectroscopic and redox properties of cdse nanocrystals in solution : The role of defect states. / Amelia, Matteo; Impellizzeri, Stefania; Monaco, Simone; Yildiz, Ibrahim; Silvi, Serena; Raymo, Francisco; Credi, Alberto.

In: ChemPhysChem, Vol. 12, No. 12, 22.08.2011, p. 2280-2288.

Research output: Contribution to journalArticle

Amelia, Matteo ; Impellizzeri, Stefania ; Monaco, Simone ; Yildiz, Ibrahim ; Silvi, Serena ; Raymo, Francisco ; Credi, Alberto. / Structural and size effects on the spectroscopic and redox properties of cdse nanocrystals in solution : The role of defect states. In: ChemPhysChem. 2011 ; Vol. 12, No. 12. pp. 2280-2288.
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