The Role of Length and Defects on Optical Quantum Efficiency and Exciton Decay Dynamics in Single-Walled Carbon Nanotubes

We perform Monte Carlo simulations of the time-resolved, spatially resolved, and integrated photoluminescence from a nanotube to investigate the role of the nanotube length L and defects using an exciton random-walk and defect-induced quenching model. When nonradiative decay is due solely to diffusion quenching, the quantum efficiency is approximately proportional to L 2 at low quantum efficiency. With defects present, the quantum efficiency depends only weakly on the number defects but is instead tied to L eff 2 where L eff is the root-mean-square separation between defects. The time-resolved photoluminescence decay of nanotubes is multiexponential for both pristine nanotubes and nanotubes with defects. The dominant time scale for a pristine nanotube is proportional to L 2/D, where D is the diffusion constant. The presence of defects on the nanotube introduces additional time scales.