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Summary: Transient Grating Measurements of
Excitonic Dynamics in Single-Walled
Carbon Nanotubes: The Dark Excitonic
Bottleneck
H. Ye. Seferyan, M. B. Nasr, V. Senekerimyan, R. Zadoyan, P. Collins, and
V. A. Apkarian*,
Department of Chemistry, UniVersity of California, IrVine, California 92697,
and Department of Physics and Astronomy, UniVersity of California,
IrVine, California 92697
Received July 17, 2006
ABSTRACT
Transient grating measurements affirm the excitonic model for single-walled carbon nanotubes (SWNT) by identifying the dark exciton (D) as
the population relaxation bottleneck in semiconducting-SWNT (S-SWNT). The data allow the reconstruction of the kinetics of excitonic cascade
and cooling, from band continuum to vibrational cooling in the ground electronic state. In S-SWNT, the intraband relaxation occurs in 40 fs,
localization into the 2g exciton occurs in 50 fs, followed by the excitonic cascade: 2g f 1u f D f 1g with time constants of 175 fs, 3 ps, 300
ps, respectively. Fluorescence from the 1u state is quenched by efficient population transfer to 1D dark exciton. In metallic tubes, cooling is
completed on the time scale of 1 ps.
Because of their small diameter (1 nm) and extended
dimension along the tube axis, single-walled carbon nano-
tubes (SWNTs) are characterized as quasi-one-dimensional
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