Photoluminescence clamping with few excitons in a single-walled carbon nanotube

TL;DR

This study demonstrates that single-walled carbon nanotubes exhibit photoluminescence saturation at very low exciton numbers due to efficient exciton-exciton annihilation, with detailed modeling and spectroscopy revealing key exciton dynamics.

Contribution

It provides new insights into exciton behavior in carbon nanotubes, combining experimental and stochastic modeling approaches to understand PL clamping at low exciton counts.

Findings

Photoluminescence saturates at 2-6 excitons per pulse.

Exciton lifetime measured at approximately 85 ps.

Absorption efficiency of nanotubes is 2-6%.

Abstract

Single air-suspended carbon nanotubes (length 2 - 5 microns) exhibit high optical quantum efficiency (7 - 20%) for resonant pumping at low intensities. Under ultrafast excitation, the photoluminescence dramatically saturates for very low injected exciton numbers (2 to 6 excitons per pulse per SWCNT). This PL clamping is attributed to highly efficient exciton-exciton annihilation over micron length scales. Stochastic modeling of exciton dynamics and femtosecond excitation correlation spectroscopy allow determination of nanotube absorption (2 - 6%) and exciton lifetime (85 +- 20 ps).