Tuning the Optical Band Gap of Quantum Dot Assemblies by Varying Network Density
- 2 July 2009
- journal article
- Published by American Chemical Society (ACS) in ACS Nano
- Vol. 3 (7), 2000-2006
- https://doi.org/10.1021/nn900456f
Abstract
The effect of bulk network density on the extent of quantum confinement (probed by optical band gap) in CdSe quantum dot gels is evaluated. The CdSe gels were produced from controlled removal of surface thiolate ligands from CdSe quantum dots by adding 3% tetranitromethane. Two main techniques were employed to systematically vary the bulk density. First, different amounts of oxidizing agent were added to change the monolith density of the wet gel, followed by supercritical CO(2) drying to yield CdSe aerogels with different bulk densities. Experimental results suggest that a gradual and almost linear band gap decrease is observed when increasing the bulk density at the aerogel level. The fact that quantum confinement effects are largely preserved in aerogel constructs is consistent with SAXS data revealing the fractal nature of the network. Second, for a constant amount of oxidant, different drying techniques were used to yield CdSe gels with a larger density variation: aerogels (supercritical CO(2) dried), ambigels (hexane dried), and xerogels (acetone dried). A nonlinear trend for band gap decrease was found when comparing CdSe aerogels, ambigels, and xerogels, and the more dense ambi- and xerogels have broader absorption edges, suggestive of resonance transfer effects due to dipole-dipole interactions in non-homogeneous interacting systems. This is attributed to increased aggregation in the denser constructs (supported by TEM and SAXS data). Together, these data suggest that highly porous architectures, such as aerogels, are best suited for maintaining localized quantum confinement effects in 3D connected nanoparticle networks.Keywords
This publication has 27 references indexed in Scilit:
- Engineering Strength, Porosity, and Emission Intensity of Nanostructured CdSe Networks by Altering the Building-Block ShapeJournal of the American Chemical Society, 2008
- Highly Luminescent Quantum-Dot MonolithsJournal of the American Chemical Society, 2007
- METAL CHALCOGENIDE GELS, XEROGELS AND AEROGELSComments on Inorganic Chemistry, 2006
- Sol−Gel Assembly of CdSe Nanoparticles to Form Porous Aerogel NetworksJournal of the American Chemical Society, 2006
- Sol−Gel Processing of Semiconducting Metal Chalcogenide Xerogels: Influence of Dimensionality on Quantum Confinement Effects in a Nanoparticle NetworkChemistry of Materials, 2005
- Comparative study using small-angle x-ray scattering and nitrogen adsorption in the characterization of silica xerogels and aerogelsPhysical Review B, 2004
- Two- versus three-dimensional quantum confinement in indium phosphide wires and dotsNature Materials, 2003
- Electrically conductive oxide aerogels: new materials in electrochemistryJournal of Materials Chemistry, 2001
- Aerogels—Airy Materials: Chemistry, Structure, and PropertiesAngewandte Chemie-International Edition, 1998
- Simultaneous monitoring of amorphous and crystalline phases in silicalite precursor gels. An in situ hydrothermal and time-resolved small- and wide-angle X-ray scattering studyJournal of Applied Crystallography, 1994