Photoluminescence sidebands of carbon nanotubes below the bright singlet excitonic levels: Coupling between dark excitons and K-point phonons

TL;DR

This study uses photoluminescence spectroscopy to identify a consistent emission sideband in single-walled carbon nanotubes, attributed to dark exciton and phonon coupling, revealing insights into excitonic interactions.

Contribution

It demonstrates the existence of a universal PL sideband in SWNTs and attributes it to dark exciton and K-point phonon coupling, expanding understanding of excitonic states.

Findings

PL sideband at ~145 meV below E11 observed across different SWNT types

Sideband energy is nearly independent of nanotube diameter

Coupling between dark excitons and K-point LO phonons is identified as the origin

Abstract

We performed detailed photoluminescence (PL) spectroscopy studies of three different types of single-walled carbon nanotubes (SWNTs) by using samples that contain essentially only one chiral type of SWNT, (6,5), (7,5), or (10,5). The observed PL spectra unambiguously show the existence of an emission sideband at ~ 145 meV below the lowest singlet excitonic (E11) level, whose identity and origin are now under debate. We find that the energy separation between the E11 level and the sideband is almost independent of the SWNT diameter. Based on this, we ascribe the origin of the observed sideband to coupling between K-point LO phonons and dipole-forbidden dark excitons, as recently suggested based on the measurement of (6,5) SWNTs.