# High efficiency dark-to-bright exciton conversion in carbon nanotubes

## TL;DR

This study reveals that dark excitons in carbon nanotubes can efficiently convert to bright excitons, significantly impacting emission properties and offering avenues for surface-engineered optoelectronic applications.

## Contribution

It demonstrates high dark-to-bright exciton conversion efficiency in carbon nanotubes and explores how surface interactions enhance this process.

## Key findings

- Dark excitons contribute significantly to emission intensity.
- Dark-to-bright transition rates are high and chirality-dependent.
- Adsorbed air molecules enhance conversion efficiency.

## Abstract

We report that dark excitons can have a large contribution to the emission intensity in carbon nanotubes due to an efficient exciton conversion from a dark state to a bright state. Time-resolved photoluminescence measurements are used to investigate decay dynamics and diffusion properties of excitons, and we obtain intrinsic lifetimes and diffusion lengths of bright excitons as well as diffusion coefficients for both bright and dark excitons. We find that the dark-to-bright transition rates can be considerably high, and that more than half of the dark excitons can be transformed into the bright excitons. The state transition rates have a large chirality dependence with a family pattern, and the conversion efficiency is found to be significantly enhanced by adsorbed air molecules on the surface of the nanotubes. Our findings show the nontrivial significance of the dark excitons on the emission kinetics in low dimensional materials, and demonstrate the potential for engineering the dark-to-bright conversion process by using surface interactions.