Many-particle excitations in non-covalently doped single-walled carbon nanotubes

Abstract

Doping of single-walled carbon nanotubes leads to the formation of new energy levels which are able to participate in optical processes. Here, we investigate (6,5)-single walled carbon nanotubes doped in a solution of hydrochloric acid using optical absorption, photoluminescence, and pump-probe transient absorption techniques. We find that, beyond a certain level of doping, the optical spectra of such nanotubes exhibit the spectral features related to two doping-induced levels, which we assign to a localized exciton and a trion T, appearing in addition to an ordinary exciton . We evaluate the formation and relaxation kinetics of respective states and demonstrate that the kinetics difference between E1 and X energy levels perfectly matches the kinetics of the state T. This original finding evidences the formation of trions through nonradiative relaxation via the level, rather than via a direct optical excitation from the ground energy state of nanotubes.

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

“…Absorption spectra also feature a doping-induced band at 1.058 eV, which is frequently attributed to a three-particle trion 19,21,23,38,39,43−47 and sometimes to a many-particle exciton-polaron state. 36,48 We designate this band as the X + trion, in line with the prevailing sentiment in the literature as well as our earlier findings, which do not reveal any noticeable shift of the band position with doping level. 23,38 The attribution of the doping-induced band at 1.058 eV to a trion state is also consistent with the previously reported inhomogeneous nature of redox-chemical doping of (6,5) s-SWNTs, with surplus charges being trapped by shallow Coulomb wells.…”

“…Second, the trion population does not seem to be subject to a slow recovery of the ground state, at least not to the extent that this affects the photobleach of the exciton band in Figure a. This phenomenon is consistent with the previous assertion of partially decoupled ground states of the exciton and trion manifolds and serves as additional evidence supporting the localized nature of surplus charges at low doping levels …”

“…Absorption spectra also feature a doping-induced band at 1.058 eV, which is frequently attributed to a three-particle trion 19,21,23,38,39,43−47 and sometimes to a many-particle exciton-polaron state. 36,48 We designate this band as the X + trion, in line with the prevailing sentiment in the literature as Figure 1. Absorption spectra of p-doped SWNTs.…”

“…This phenomenon is consistent with the previous assertion of partially decoupled ground states of the exciton and trion manifolds 23 and serves as additional evidence supporting the localized nature of surplus charges at low doping levels. 48 Correlation of Carrier Concentrations from Dynamical and Spectral Analyses. One of the significant finding of this work lies in establishing a direct correlation between dynamical and spectral modifications induced by doping.…”

Photoinduced electron transfer processes of single-wall carbon nanotube (SWCNT)–based hybrids

“…The SWCNT (•+)n transient state nature was confirmed by adding the chemical oxidant (0.5 mm K 2 IrCl 6 [60,61]. More recent studies have shown that, this ∼1150 nm band is related to exciton polaron species, i.e., excitons dressed in the Fermi sea of charge carriers; and due to this reason, both the so-called "electron polaron" and "hole polaron" share the same spectroscopic signatures at ∼1150 nm [62][63][64]. Transient absorption bands centered at 625-800 nm and 880-950 nm are assigned to the polymer radical anion (Figure 6b).…”