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Monday, September 15, 2008
10:00 AM - 11:00 AM
CNLS Conference Room (TA-3, Bldg 1690)

Seminar

Nonradiative Decay Channels in Semiconducting Single-Walled Carbon Nanotubes

Bradley F. Habenicht
Chemistry Department, University of Washington

As shown experimentally, strong nonradiative decay channels exist in carbon nanotubes (CNT) and are responsible for low fluorescence yields. The decay of the electronic excitation to its ground state is simulated in the (6,4)semiconducting CNT with surface hopping in the Kohn-Sham representation, providing a unique time-domain atomistic description of fluorescence quenching. The simulations include direct nonradiative decay of singlet excitations to the ground state and intersystem crossings between the singlet and triplet manifolds. The direct decay of singlets in the ideal CNT is estimated to occur on a 150 ps timescale and is only weakly dependent on temperature. Intersystem crossings occur within hundreds of picoseconds to nanoseconds, and the electronic energy is deposited into high-frequency optical phonons in both cases. Vibrationally induced decoherence strongly influences the electronic relaxation. Defects decrease the excited state lifetime to tens of picoseconds, rationalizing the multiple decay timescales seen in experiments.

Host: Sergei Tretiak, T-12