Saturation of the Photoluminescence at Few-Exciton Levels in a Single-Walled Carbon Nanotube under Ultrafast Excitation

摘要

Single air-suspended carbon nanotubes (length 2-5 μm) exhibit high optical quantum efficiency (7-20%) for low intensity resonant pumping. Under ultrafast excitation (150 fs), emission dramatically saturates at very low exciton numbers (2-6), which is attributed to highly efficient exciton-exciton annihilation over micron-length scales. Similar saturation behavior for 4 ps pulse excitation shows nonlinear absorption is not a contributing factor. The absorption cross sections (0.6-1.8 × 10~(-17) cm~2/atom) are determined by fitting to a stochastic model for exciton dynamics.