Trions, Exciton Dynamics and Spectral Modifications in Doped Carbon Nanotubes: A Singular Defect-Driven Mechanism

TL;DR

This study investigates how doping affects exciton behavior and spectral properties in semiconducting carbon nanotubes, revealing a defect-driven mechanism involving charge trapping, exciton confinement, and trion formation.

Contribution

It provides a mechanistic understanding of doping effects on exciton dynamics and spectral modifications in carbon nanotubes through combined spectroscopic and modeling approaches.

Findings

Charge localization and barriers can be quantified with exciton transport models.

Counterions trap charges, creating quenching sites and exciton barriers.

Trion states are hosted by exohedral counterions.

Abstract

Doping substantially influences the electronic and photophysical properties of semiconducting single-wall carbon nanotubes (s-SWNTs). Although prior studies have noted that surplus charge carriers modify optical spectra and accelerate non-radiative exciton decay in doped s-SWNTs, a direct mechanistic correlation of trion formation, exciton dynamics and energetics remains elusive. This work examines the influence of doping-induced non-radiative decay and exciton confinement on s-SWNT photophysics. Using photoluminescence, continuous-wave absorption, and pump-probe spectroscopy, we show that localization of and barrier formation by trapped charges can be jointly quantified using diffusive exciton transport- and particle-in-the-box models, yielding a one-to-one correlation between charge carrier concentrations derived from these models. The study highlights the multifaceted role of exohedral counterions, which trap charges to create quenching sites, form barriers to exciton movement, and host trion states. This contributes significantly to understanding and optimizing the photophysical properties of doped SWNTs.