pubs.acs.org/JPCL
Four-Fold Enhancement of the Activation Energy for Nonradiative Decay of Excitons in PbSe/CdSe Core/Shell versus PbSe Colloidal Quantum Dots Keith A. Abel,†,# Haijun Qiao,‡,# Jeff F. Young,‡ and Frank C. J. M. van Veggel*,† †
Department of Chemistry, University of Victoria, Victoria, British Columbia, Canada V8W 3V6, and ‡Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
ABSTRACT PbSe/CdSe core/shell quantum dots (QDs) were prepared and investigated as thick films using temperature-dependent photoluminescence. In addition to increased photostability, the CdSe shell leads to a four-fold increase of the activation energy for nonradiative exciton decay for the core/shell QDs compared to that for the bare PbSe QDs. The onset for exponential decay of luminescence is ∼240 K in the core/shell samples. From further analysis of the temperaturedependent photoluminescence shift and emission line width, we find that the cation exchange reaction broadens the QD size distribution and increases the temperature-independent state broadening. However, the temperature-dependent contribution to the line shape of the core/shell QDs is similar to that in the cores. SECTION Nanoparticles and Nanostructures
ead chalcogenide (PbSe, PbS, PbTe) colloidal quantum dots (QDs) are currently receiving widespread attention because of their size-quantized optical transitions in the near-infrared (NIR) spectral region (between 1 and 3 μm).1-4 These systems are actively explored in various applications such as light-emitting diodes and inorganic solar cells, as well as for sensor and biological imaging applications.5-7 Tunable emission at optical communication wavelengths (1.3 and 1.55 μm) means that lead chalcogenide QDs could play a role in future nanoelectronics and quantum optics applications, and recent studies have already utilized these QDs in cavity quantum electrodynamics studies.8-10 Despite their advantages, lead chalcogenide QDs have an inherent instability when stored under ambient conditions, presumably because of oxidation occurring at the QD surface.11 CdSe QDs are typically capped by growing an inorganic shell of a wider band gap semiconductor, such as ZnS, around the core.12,13 The shell protects the core against oxidation and removes surface defects/traps on the core, and the wider band gap material ensures that the electrons and holes are confined to the core. However, growth of a shell around the core of lead chalcogenide QDs has proven difficult as they are much more sensitive to heating in solution than CdSe QDs. Recent work by Hollingsworth and co-workers showed that PbSe/CdSe core/shell QDs can be prepared at lower temperatures (
