Colloidal Single-Sized Nanocrystal Ensemble Exhibits Bright, Narrow-Band PL
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of ice crystals that had previously been beyond the ability of current ice crystal scattering instruments to characterize. The researchers said that this instrument is designed to be used for laboratory studies, as cited here, and also can be mounted on aircraft with specially designed fuselage ports for studies of ambient air. TARA D. WASHINGTON
Colloidal Single-Sized Nanocrystal Ensemble Exhibits Bright, Narrow-Band PL
PL Int (a.u.)
Absorption OD
Nanocrystals and nanoparticles are currently of great interest for a variety of applications, ranging from precision polishing of surfaces to bio-oriented, energyassociated, environmental-related, and security-allied applications. In particular, colloidal semiconductor quantum dots, which are ultra-small nanocrystals and spherical in shape, have demonstrated excellent optical properties such as narrow photoemission and broad absorption, and thus create potential for new applications as well as to replace traditional fluorescence dye molecules in existing areas. Most processes for synthesis of colloidal quantum dots yield a dispersion of particle sizes, which results in photoemission linewidths (e. g., ~30 nm) that are substantially broader (due to inhomogeneous broadening) than the linewidth of a single quantum dot. K. Yu and colleagues at the National Research Council of Canada have now synthesized single-sized nanocrystal ensembles exhibiting bright bandgap photoluminescence (PL) but with bandwidth as narrow as that from a single quantum dot (e.g., ~10 nm). Yu’s group has developed a methodology of molecular synthesis for the precise formation of colloidal semiconductor nanocrystals using a synthetic approach
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Figure 1. CdSe magic-sized nanocrystal Family 463 dispersed in toluene demonstrates pure-color light absorption (blue line, right y axis) and emission (red line, left y axis). Reprinted with permission from the Journal of Physical Chemistry C 112(36) (2008) p. 13805. ©2008 American Chemical Society.
analogous to bottom-up self-assembly. This research group specializes in the development of colloidal single-sized nanocrystal ensembles, also called magicsized nanocrystal (MSN) ensembles, using semiconductor quantum dots such as cadmium selenide (CdSe). The MSN ensembles have the special optical property of sharp light absorption near the absorption band edge and pure-color emission due to the absence of inhomogeneous broadening rising from their single-size property, with an optical response equivalent to one single quantum dot. The group’s latest nanotechnology results on molecular synthesis were reported in the September 11 issue of the Journal of Physical Chemistry C (DOI: 10.1021/ jp803845n; p. 13805). The molecular synthesis of single-sized ensembles simplifies handling and promises to be practical in large-scale production with high reproducibility. This ready approach uses a fatty acid as surface ligands, with 1-octadecene as the reaction medium. For CdSe, cadmium acetate dihydrate and elemental selenium are the source
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