Exciton transfer and propagation in carbon nanotubes studied by near-field optical microscopy

We studied transfer and propagation of excitons in single semiconducting carbon nanotubes using high resolution tip-enhanced near-field photoluminescence microscopy. Exciton energy transfer is found to occur from a larger band gap nanotube to a smaller band gap nanotube. Efficient transfer however is found to be limited to a few nanometers because of competing fast non-radiative relaxation and can be explained in terms of electromagnetic near-field coupling. Towards the end of a nanotube, photoluminescence decay is observed on a length scale of 50-90 nm which is attributed to exciton propagation followed by additional non-radiative relaxation at the nanotube end.