Arao Nakamura

Ultrafast exciton energy transfer between nanoscale coaxial cylinders: intertube transfer and luminescence quenching in double-walled carbon nanotubes.

We study exciton energy transfer in double-walled carbon nanotubes using femtosecond time-resolved luminescence measurements. From direct correspondence between decay of the innertube luminescence and the rise behavior in outertube luminescence, it is found that the time constant of exciton energy transfer from the inner to the outer semiconducting tubes is ∼150 fs. This ultrafast transfer indicates that the relative intensity of steady-state luminescence from the innertubes is ∼700 times weaker than that from single-walled carbon nanotubes.

One‐Dimensional Characteristics of Third‐Order Nonlinear Optical Response in Single‐Walled Carbon Nanotubes

Third‐order nonlinear optical susceptibilities have been investigated for individually suspended single walled carbon nanotubes in solution. The imaginary part of susceptibility Imχ(3) shows the resonant enhancement at each optical transition of the specific (n,m) tube. We have found that the diameter D dependence of the figure of merit Imχ(3)/α (α:absorption coefficient) is D6.1±0.9.

Exciton Energy Transfer between Single‐Walled Carbon Nanotubes in Femtosecond Regime

We investigated luminescence decay kinetics in single‐walled carbon nanotubes in large bundles excited by femtosecond pulses. The time constant of luminescence decay becomes longer with decrease of photon energy. This behavior is explained by exciton energy transfer from an excited to neighboring tubes.

Enhancement of Third‐Order Optical Nonlinearities in Carbon Nanotubes by Encapsulated Fullerenes

Third‐order nonlinear optical responses in single walled carbon nanotubes (SWNTs) encapsulating C70‐ or C84‐ molecules have been investigated by means of pump‐probe spectroscopy. It is found that the nonlinear optical response due the exciton transition is enhanced for SWNTs encapsulating C84‐molecules. The enhancement mechanism is interpreted in terms of hybridization of C84‐molecular states and SWNT band states.

Nonlinear Optical Response in Single‐Walled Carbon Nanotubes under Resonant Excitation Conditions

Third‐order nonlinear optical responses in single walled carbon nanotubes have been investigated by means of pump‐probe spectroscopy with various excitation conditions. In the excitation spectra of nonlinear susceptibilities probed at the E22 transition energy of the (8, 4) tube, an additional peak is observed at ∼0.2 eV above the E22 transition energy. It is found that the phonon‐assisted transition is involved in the third‐order nonlinear optical processes.