7 research outputs found
Structure-Dependent Fluorescence Efficiencies of Individual Single-Walled Carbon Nanotubes
Single-nanotube photometry was used to measure the product of absorption
cross-section and fluorescence quantum yield for 12 (n,m) structural species of
semiconducting SWNTs in aqueous SDBS suspension. These products ranged from 1.7
to 4.5 x 10(-19) cm2/C atom, generally increasing with optical band gap as
described by the energy gap law. The findings suggest fluorescent quantum
yields of ~8% for the brightest, (10,2) species and introduce the empirical
calibration factors needed to deduce quantitative (n,m) distributions from bulk
fluorimetric intensities
Stepwise Quenching of Exciton Fluorescence in Carbon Nanotubes by Single Molecule Reactions
Single-molecule chemical reactions with individual single-walled carbon
nanotubes were observed through near-infrared photoluminescence microscopy. The
emission intensity within distinct submicrometer segments of single nanotubes
changes in discrete steps after exposure to acid, base, or diazonium reactants.
The steps are uncorrelated in space and time, and reflect the quenching of
mobile excitons at localized sites of reversible or irreversible chemical
attack. Analysis of step amplitudes reveals an exciton diffusional range of
about 90 nanometers, independent of nanotube structure. Each exciton visits
approximately 104 atomic sites during its lifetime, providing highly efficient
sensing of local chemical and physical perturbations
Diameter-dependent bending dynamics of single-walled carbon nanotubes in liquids
By relating nanotechnology to soft condensed matter, understanding the mechanics and dynamics of single-walled carbon nanotubes (SWCNTs) in fluids is crucial for both fundamental and applied science. Here, we study the Brownian bending dynamics of individual chirality-assigned SWCNTs in water by fluorescence microscopy. The bending stiffness scales as the cube of the nanotube diameter and the shape relaxation times agree with the semiflexible chain model. This suggests that SWCNTs may be the archetypal semiflexible filaments, highly suited to act as nanoprobes in complex fluids or biological systems
Length- and Defect-Dependent Fluorescence Efficiencies of Individual Single-Walled Carbon Nanotubes
Using near-infrared fluorescence videomicroscopy with spectrally selective excitation and imaging, more than 400 individual (10,2) single-walled carbon nanotubes (SWCNTs) have been studied in unsorted liquid dispersions. For each nanotube, the spatially integrated emission intensity was measured under controlled excitation conditions while its length was found either from direct imaging or from the diffusion coefficient computed by analyzing its Brownian motion trajectory. The studied nanotubes ranged in length from 170 to 5300 nm. For any length, a wide variation in emission intensities was observed. These variations are attributed to differing densities of nanotube imperfections that cause fluorescence quenching. The brightest nanotubes at each length (presumed near-pristine) show total emission nearly proportional to length. This implies a nearly constant fluorescence quantum yield and a constant absorption cross section per carbon atom, validating conventional Beer–Lambert analysis for finding concentrations of SWCNT species. Ensemble-averaged emission is also proportional to length, but at only <i>ca.</i> 40% of the near-pristine values. Further research is needed to investigate the extrinsic effects causing wide variation in quantum yields and assess their implications for SWCNT fluorimetry