Incidence of Quantum Confinement on Dark Triplet Excitons in Carbon Nanotubes

Abstract

The photophysics of single-wall carbon nanotubes (SWCNTs) is intensively studied due to their potential application in light harvesting and optoelectronics. Excited states of SWCNTs form strongly bound electron–hole pairs, excitons, of which only singlet excitons participate in application relevant optical transitions. Long-living spin-triplet states hinder applications, but they emerge as candidates for quantum information storage. Therefore, knowledge of the triplet exciton energy structure, in particular in a SWCNT chirality dependent manner, is greatly desired. We report the observation of light emission from triplet state recombination, i.e., phosphorescence, for several SWCNT chiralities using a purpose-built spectrometer. This yields the singlet–triplet gap as a function of the SWCNT diameter, and it follows predictions based on quantum confinement effects. Saturation under high microwave power (up to 10 W) irradiation allows the spin-relaxation time for triplet states to be determined. Our study sensitively discriminates whether the lowest optically active state is populated from an excited state on the same nanotube or through Förster exciton energy transfer from a neighboring nanotube.

Formation of organic color centers in air-suspended carbon nanotubes using vapor-phase reaction

“…5 c, d. The dependence shows a monotonic decrease and differs from the constant energy separation of 130 meV for the K -momentum excitons, and we thus exclude them from the origin of E and E . To describe the dependence, we consider the 1/ d scaling observed for the exciton binding energies and the 1/ d 2 scaling for singlet-triplet splitting 40 – 44 (Supplementary Note 5 ). The 1/ d 2 scaling yields better fits to both and than the 1/ d scaling.…”

Delayed Fluorescence from Carbon Nanotubes through Singlet Oxygen-Sensitized Triplet Excitons

“…We infer that these species have their lowest triplet exciton energies near 972 meV, giving estimated gaps to the bright singlet exciton of approximately 125 meV. This energy gap value is similar to the values of ∼80 to 90 meV reported from computations and from experiment, but it is significantly larger than energy gaps of ∼45 meV found in a recent ODMR phosphorescence study conducted under somewhat different sample conditions . However, we note that the emissive triplet exciton observed in ODMR phosphorescence likely lies above the triplet that is excited in our energy transfer process.…”

Interaction of Luminescent Defects in Carbon Nanotubes with Covalently Attached Stable Organic Radicals

“…The presence of the radical leads to partial quenching of defect PL, which is likely due to a combination of a photoinduced electron transfer process and population transfer to triplet states enabled by radical-enhanced intersystem crossing. Consequently, radical-functionalized sp 3 defects are an interesting platform for future studies of the elusive triplet exciton manifold in carbon nanotubes employing spin-sensitive methods such as optically detected magnetic resonance. , Moreover, as pulsed EPR techniques can probe the distances between spin labels on the length scale of a few nanometers, such defects could be a model system for investigating clustering, which is suspected to play an important part in both synthetic , and optical features of luminescent defects. Beyond that, the encapsulation of such radical-tailored SWCNTs in biocompatible surfactants might even enable their use as metal-free contrast agents for magnetic resonance imaging , complementary to in vivo near-infrared fluorescence imaging .…”