Publications (12) View all
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Article: Giant and Broadband Absorption Enhancement in Colloidal Quantum Dot Monolayers through Dipolar Coupling.
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ABSTRACT: The absorption cross section of colloidal quantum dots in close packed monolayers shows a 4 (CdSe) to 5-fold (PbS) enhancement as compared to quantum dots in a dilute dispersion. Quantitative agreement is demonstrated between the value and the size dependence of the enhancement and theoretical model predictions based on dipolar coupling between neighboring quantum dots. This collective optical behavior offers a new degree of freedom in the custom design of optical properties for electro-optical devices.ACS Nano 01/2013; · 10.77 Impact Factor -
Article: Multiple dot-in-rod PbS/CdS heterostructures with high photoluminescence quantum yield in the near-infrared.
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ABSTRACT: Pb cations in PbS quantum rods made from CdS quantum rods by successive complete cationic exchange reactions are partially re-exchanged for Cd cations. Using STEM-HAADF, we show that this leads to the formation of unique multiple dot-in-rod PbS/CdS heteronanostructures, with a photoluminescence quantum yield of 45-55%. We argue that the formation of multiple dot-in-rods is related to the initial polycrystallinity of the PbS quantum rods, where each PbS crystallite transforms in a separate PbS/CdS dot-in-dot. Effective mass modeling indicates that electronic coupling between the different PbS conduction band states is feasible for the multiple dot-in-rod geometries obtained, while the hole states remain largely uncoupled.Journal of the American Chemical Society 03/2012; 134(12):5484-7. · 9.91 Impact Factor -
Article: Multiple Dot-in-Rod PbS/CdS Heterostructures with High Photoluminescence Quantum Yield in the Near-Infrared
Journal of the American Chemical Society 03/2012; · 9.91 Impact Factor -
Article: Phase transitions in quantum-dot Langmuir films.
Angewandte Chemie International Edition 12/2011; 50(50):12058-61. · 13.45 Impact Factor -
Article: Size-tunable, bright, and stable PbS quantum dots: a surface chemistry study.
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ABSTRACT: PbS Qdots are synthesized using PbCl2 and elemental sulfur as precursors. The available size range is significantly expanded using tri-n-octylphosphine (TOP), enabling the synthesis of monodisperse suspensions of Qdots with a mean size varying between 3 and 10 nm. The ligand composition and dynamics are investigated with nuclear magnetic resonance (NMR) spectroscopy. We show that the Qdots are passivated solely by highly dynamic OlAm ligands, even when TOP is employed during synthesis. In this respect, TOP is a compound strongly modifying the Qdot synthesis, without affecting the final Qdot surface chemistry. Next, the OlAm ligands are exchanged for oleic acid (OlAc). NMR data show that the OlAc ligands are tightly bound to the Qdot surface, with a coverage of 3.0±0.4 nm(-2). In addition, we demonstrate that they are bound as oleate ions. Combining this with the inorganic Qdot composition, we observe that charge-neutral Qdots are obtained when taking into account the charge of the stoichiometric PbS Qdot core, the surface excess of Pb ions, the surface-adsorbed Cl ions and the oleate ligands. The Qdot suspensions are stable under atmospheric conditions, showing no changes in the NMR and absorbance spectra for several weeks. Finally, we determine the photoluminescence quantum yield (PL QY) for OlAc-capped PbS Qdots, synthesized either with or without TOP. In both cases, they are highly luminescent, with PL QY values varying between 20 and 90%, depending on the Qdot size.ACS Nano 02/2011; 5(3):2004-12. · 10.77 Impact Factor
