Effect of environment on ultrafast photoexcitation kinetics in single‐wall carbon nanotubes

Recently, nonlinear optical properties of single-wall carbon nanotubes (SWNT) have attracted a great interest. This material has been proven to be an efficient wide spectral range saturable absorber. However, up to now it is unclear what are the optimum sample preparation parameters and operational spectral range. In this work, we have applied femtosecond pump–probe spectroscopy to investigate photoexcitation kinetics in SWNTs depending on the sample preparation technique. We demonstrate here that the characteristic lifetimes of the saturable absorption in SWNT samples decrease with increasing interaction of SWNTs with each other and with the surrounding environment. We also show that the saturable absorption is fairly strong not only for the energies corresponding to the first electronic transition, but also for transitions at higher energies. We conjecture the contribution of energy and charge transfer to the observed ultrafast dynamics. Charge transfer is evidenced by a photo-induced enhancement of the Sommerfeld factor.