Web Release Date: June 7,
Quantum Yield Heterogeneities of Aqueous Single-Wall Carbon Nanotube Suspensions
and
Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602, and Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee 37235
Received March 5, 2007
Abstract:
Aqueous suspensions of single-wall carbon nanotubes (SWNTs) prepared by traditional methods from the supernatant of ultracentrifuged micellar SWNT mixtures are shown to be strongly heterogeneous with respect to the quantum yield of their constituents. The heterogeneities are isolated using preparative ultracentrifugation in iodixanol density gradients and are optically characterized by photoluminescence and linear absorption spectroscopy. We find that the most buoyant fractions with a density of 1.055 ± 0.005 g·cm-3 have the highest photoluminescence quantum yield 
of 1.1%, a factor of 5 higher than that of the supernatant. Denser fractions with lower make up for about 2/3 of these samples and contain mostly small ropes in which the quantum yield is reduced by nonradiative decay through coupling to metallic tubes.
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