Confirmation of K-Momentum Dark Exciton Vibronic Sidebands Using ¹³C-labeled, Highly Enriched (6,5) Single-walled Carbon Nanotubes

Abstract

A detailed knowledge of the manifold of both bright and dark excitons in single-walled carbon nanotubes (SWCNTs) is critical to understanding radiative and nonradiative recombination processes. Exciton-phonon coupling opens up additional absorption and emission channels, some of which may "brighten" the sidebands of optically forbidden (dark) excitonic transitions in optical spectra. In this report, we compare (12)C and (13)C-labeled SWCNTs that are highly enriched in the (6,5) species to identify both absorptive and emissive vibronic transitions. We find two vibronic sidebands near the bright (1)E(11) singlet exciton, one absorptive sideband ~200 meV above, and one emissive sideband ~140 meV below, the bright singlet exciton. Both sidebands demonstrate a ~50 cm(-1) isotope-induced shift, which is commensurate with exciton-phonon coupling involving phonons of A[Formula: see text] symmetry (D band, ω ~ 1330 cm(-1)). Independent analysis of each sideband indicates that both sidebands arise from the same dark exciton level, which lies at an energy approximately 25 meV above the bright singlet exciton. Our observations support the recent prediction of, and mounting experimental evidence for, the dark K-momentum singlet exciton lying ~25 meV (for the (6,5) SWCNT) above the bright Γ-momentum singlet. This study represents the first use of (13)C-labeled SWCNTs highly enriched in a single nanotube species to unequivocally confirm these sidebands as vibronic sidebands of the dark K-momentum singlet exciton.

Survey of exciton-phonon sidebands by magneto-optical spectroscopy using highly specified (6,5) single-walled carbon nanotubes

“…Furthermore, our value compares well with the experimental values of 25 meV and 29 meV reported recently [14,18].Consistency between these data clearly shows the high experimental accuracy of our measurements.…”

“…From these EMG fittings, we deduced that the actual peak position of X2 (pink vertical line in Fig. 3(c)) is shifted by ~ 19.6 meV from the peaks observed in the magneto-absorption spectra, which is in good agreement with the value given by Ref [18] and slightly larger than the value of 11 meV from Ref [14].…”

“…What is important is that, the actual peak position, E X2 , is shifted to higher energy because of the convolution. To extract the actual peak energy precisely, we followed the procedure employed in Refs [14,15,18] and utilized in our fitting the exponentially modified Gaussian (EMG) function, whose waveform is as follow [28][29]:…”

Exciton-phonon bound complex in single-walled carbon nanotubes revealed by high-field magneto-optical spectroscopy

“…In the case of the 1st sub-band transitions, there has been intense debate about the origin of the phonon sidebands, and it was confirmed recently that the D-K-S exciton is responsible for the observed phonon sidebands [7,8]. In the following, we would follow the procedure as employed in our previous work [8] to analyze the origin of the E 22 phonon sideband.…”

“…In the case of the D-K-S exciton, phonon sidebands were believed to originate from the D-K-S exciton coupling with the zone-boundary A ′ 1 symmetry phonon [7,[19][20][21][22]. Energy of this D-K-S exciton (E K ) remains constant in magnetic fields within the available field range [13].…”