We present evidence of all optical trion generation and emission in undoped single walled carbon nanotubes (SWCNTs). Luminescence spectra, recorded on individual SWCNTs over a large CW excitation intensity range, show trion emission peaks red-shifted with respect to the bright exciton peak. Clear chirality dependence is observed for 22 separate SWCNT species, allowing for determination of electron-hole exchange interaction and trion binding energy contributions.Luminescence data together with ultrafast pump probe experiments on chirality sorted bulk samples suggest that exciton-exciton annihilation processes generate dissociated carriers that allow for trion creation upon a subsequent photon absorption event.It is well established that the optical properties of semiconducting single walled carbon nanotubes (SWCNTs) are dominated by tightly bound one-dimensional excitons [1,2]. The recombination of these excitons results in narrow emission peaks. As it dominates the luminescence spectra, the lowest lying optically active exciton in SWCNTs has attracted much experimental and theoretical attention over the past decade [3]. Since SWCNTs consist only of surface atoms, exciton dynamics, and hence nanotube luminescence intensity, are extremely sensitive to the local environment and the presence of quenching sites or structural defects [4,5]. Such extrinsic effects are thought to be responsible for the fairly short luminescence lifetimes (100 ps or less [4,6]) and low luminescence quantum yields (of a few percent) reported for individual SWCNTs in the low excitation intensity regime [6,7].For sufficiently strong CW or pulsed excitation intensities multiple excitons are likely to exist simultaneously. In this regime, nanotube photophysics is governed by the interplay between onedimensional exciton diffusion along the nanotube sidewall [5] and strong coulomb interactions between carriers. When two or more excitons are present, their interaction can lead to two different situations. On one hand, they can undergo Auger processes such as exciton-exciton annihilation (EEA) which open-up additional, efficient nonradiative recombination pathways. Experimental evidence for this has been reported by several groups using ultrafast spectroscopy on ensemble samples [8,9 ]. On the other hand, excitons may form many-body bound states. Theorists have predicted biexcitons to have a binding energy larger than the thermal energy k B T [10,11]. No experimental evidence for these bound states has been reported so far, however, in agreement with recent theoretical studies [12].Charged excitons, or trions, are another class of many-body bound states predicted to possess a significant binding energy in SWCNTs [13]. Very recently, Matsunaga et al.[14] observed new spectral features in p-doped nanotube suspensions, which have been assigned to hole-exciton bound states (positively charged trions).Here we show that trions can be efficiently generated, on demand and in-situ, in highly luminescent undoped carbon nanotubes through control of photo-e...

We present a study of free carrier photogeneration and multicarrier bound states, such as biexcitons and trions (charged excitons), in semiconducting single-walled carbon nanotubes. Pump-and-probe measurements performed with fs pulses reveal the effects of strong Coulomb interactions between carriers on their dynamics. Biexciton formation by optical transition from exciton population results in an induced absorption line (binding energy 130 meV). Exciton-exciton annihilation process is shown to evolve at high densities towards an Auger process that can expel carriers from nanotubes. The remaining carriers give rise to an induced absorption due to trion formation (binding energy 190 meV). These features show the dynamics of exciton and free carriers populations.