Unifying the low-temperature photoluminescence spectra of carbon nanotubes: the role of acoustic phonon confinement

TL;DR

This paper investigates the low-temperature photoluminescence spectra of single-wall carbon nanotubes, revealing that variations in acoustic phonon modes, including confinement effects, explain the spectral diversity observed.

Contribution

It provides a comprehensive set of photoluminescence profiles and demonstrates how modifications in acoustic phonon modes influence spectral features, including the emergence of narrow lines.

Findings

Diversity in spectra arises from modifications in acoustic phonon modes.

Suppression of low-energy modes yields ultra-narrow emission lines.

Confined phonon modes cause multi-peak temperature-dependent profiles.

Abstract

At low temperature the photoluminescence of single-wall carbon nanotubes show a large variety of spectral profiles ranging from ultra narrow lines in suspended nanotubes to broad and asymmetrical line-shapes that puzzle the current interpretation in terms of exciton-phonon coupling. Here, we present a complete set of photoluminescence profiles in matrix embedded nanotubes including unprecedented narrow emission lines. We demonstrate that the diversity of the low-temperature luminescence profiles in nanotubes originates in tiny modifications of their low-energy acoustic phonon modes. When low energy modes are locally suppressed, a sharp photoluminescence line as narrow as 0.7 meV is restored. Furthermore, multi-peak luminescence profiles with specific temperature dependence show the presence of confined phonon modes.