Interband Recombination Dynamics in Resonantly-Excited Single-Walled Carbon Nanotubes

TL;DR

This study uses wavelength-dependent pump-probe spectroscopy to identify two distinct carrier recombination dynamics in single-walled carbon nanotubes, revealing a slow interband process enhanced at resonance and its modulation by doping.

Contribution

It reports the first observation of a slow interband recombination component in resonantly-excited nanotubes and links it to doping-induced changes in absorption.

Findings

Slow component (5-20 ps) attributed to interband recombination.

Fast component (0.3-1.2 ps) attributed to intraband relaxation.

Doping reduces the slow component by shifting absorption peaks.

Abstract

Wavelength-dependent pump-probe spectroscopy of micelle-suspended single-walled carbon nanotubes reveals two-component dynamics. The slow component (5-20 ps), which has not been observed previously, is resonantly enhanced whenever the pump photon energy coincides with an absorption peak and we attribute it to interband carrier recombination, whereas we interpret the always-present fast component (0.3-1.2 ps) as intraband carrier relaxation in non-resonantly excited nanotubes. The slow component decreases drastically with decreasing pH (or increasing H$^+$ doping), especially in large-diameter tubes. This can be explained as a consequence of the disappearance of absorption peaks at high doping due to the entrance of the Fermi energy into the valence band, i.e., a 1-D manifestation of the Burstein-Moss effect.