Nonlinear Photoluminescence Excitation Spectroscopy of Carbon Nanotubes: Exploring the Upper Density Limit of One-Dimensional Excitons

TL;DR

This study investigates the upper density limit of one-dimensional excitons in carbon nanotubes using nonlinear photoluminescence excitation spectroscopy, revealing saturation behavior and estimating exciton densities.

Contribution

It introduces a theoretical model combining exciton diffusion and annihilation to estimate exciton densities at saturation in carbon nanotubes.

Findings

Emission peaks saturate at a species-independent value.

Estimated exciton densities are below the Mott density.

Saturation behavior differs from conventional quantum wires.

Abstract

We have studied emission properties of high-density excitons in single-walled carbon nanotubes through nonlinear photoluminescence excitation spectroscopy. As the excitation intensity was increased, all emission peaks arising from different chiralities showed clear saturation in intensity. Each peak exhibited a saturation value that was independent of the excitation wavelength, indicating that there is an upper limit on the exciton density for each nanotube species. We developed a theoretical model based on exciton diffusion and exciton-exciton annihilation that successfully reproduced the saturation behavior, allowing us to estimate exciton densities. These estimated densities were found to be still substantially smaller than the expected Mott density even in the saturation regime, in contrast to conventional semiconductor quantum wires.