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 L2 at low quantum efficiency. With defects present, the quantum efficiency depends only weakly on the number defects but is instead tied to Leff2 where Leff 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 L2/D, where D is the diffusion constant. The presence of defects on the nanotube introduces additional time scales.