Spectroscopic signatures of many-particle energy levels in non-covalently doped single-wall carbon nanotubes

We report the first observation of an optical transition from a ground trion state T to excited trion state T* in (6,5) single-wall carbon nanotubes non-covalently doped with hydrochloric acid. The position of such an excited trion level T* is estimated as 2,12 eV, while the ground trion level T has an energy of 1,08 eV. Besides, pump-probe transient absorption spectroscopy indicates that the ground trion level T cannot be excited directly. Instead, we propose that trions form after nonradioactive relaxation from excitons, dressed by interaction with doping induced hole-polarons. We also report a complete exciton-to-trion conversion by means of photoluminescence spectroscopy, thus supporting existence of the polaron-dressed exciton energy level in p-doped single-wall carbon nanotubes.