Mono- and Biexponential Luminescence Decays of Individual Single-Walled Carbon Nanotubes

Abstract

We have studied the exciton recombination dynamics of individual (6,4) and (6,5) single-walled carbon nanotubes embedded in aqueous gels or deposited on glass surfaces. CoMoCat nanotubes systematically display short monoexponential photoluminescence (PL) decays presumably due to defects introduced during their synthesis. In contrast HiPco nanotubes can either display mono-or biexponential PL decays depending on the environmental conditions. Transition from bi-to monoexponential decays can be reproduced by a simple three level model taking into account defect-dependent nonradiative decay mechanisms.The photoluminescence (PL) properties of semiconducting single walled carbon nanotubes (SWNTs) have attracted much attention over the last years.1 These properties strongly depend on the structure of each nanotube 2 but also on extrinsic factors resulting for instance from synthesis or environmental factors. 3-7As a result, PL studies performed on ensemble of SWNTs are affected by inhomogeneities that hinder the development of a detailed understanding of the underlying mechanisms. Experiments on individual SWNTs remove part of this heterogeneity by allowing description of the characteristics of each SWNT in its particular environment. 8 Comparisons between values of a physical parameter extracted from different experimental reports are however difficult because, generally, the studied samples differ by synthesis methods or preparation procedures. For example PL decays performed on individual (6,4) and (6,5) nanotubes by different groups have resulted in distinct behaviors, ranging from very short monoexponential decays to longer biexponential ones. 5,7,[9][10][11] This paper aims at understanding this large disparity in PL decay behaviors. We experimentally confirm that PL decays of (6,5) and (6,4) nanotubes can exhibit either mono-or biexponential behaviors and show that these depend on synthesis methods and nanotube environment. These observations are explained by a previous simple three-level model 10 taking now into account the defect-dependent dominant nonradiative decay mechanisms proposed by Pereibenos et al. 12The SWNTs used in this study were either synthesized using HiPco or CoMoCat methods. The nanotubes were dispersed in aqueous suspensions of the anionic surfactants sodium deoxycholate (DOC). For observations, single-molecule wide-field and confocal PL microscopes were used to image SWNTs excited with a continuous wave laser. The SWNTs were immobilized in aqueous agarose gels (5 wt %) or spin-coated on surfaces. SWNTs concentration was kept well below 1 µm -3 such that bright individual nanotubes could be optically resolved. The PL of these bright tubes was sent to a spectrometer for further spectral identifications of individual (6,4) or (6,5) nanotubes. Typically, isolated SWNTs feature narrow PL lines from their bright excitonic state E 11 , with full width at half-maximum (fwhm) in the range of ∼17-22 nm. Following identification of these bright individual nanotubes, the excitation modality was switche...

All-Optical Trion Generation in Single-Walled Carbon Nanotubes

“…Individual SWCNTs were imaged with a InGaAs camera and their luminescence spectra were recorded with a spectrometer equipped with a InGaAs detector array. These nanotubes showed bright, highly stable emission with the longest luminescence decays reported to date, signifying low defect density and reduced environmental perturbations [18].…”

“…Individual SWCNTs were imaged with a InGaAs camera and their luminescence spectra were recorded with a spectrometer equipped with a InGaAs detector array. These nanotubes showed bright, highly stable emission with the longest luminescence decays reported to date, signifying low defect density and reduced environmental perturbations [18].Bright individual nanotubes were selected (see inset of figure 1a) and their luminescence spectra were first recorded at excitation intensities in the monoexcitonic regime (well below 1 kW/cm²) (figure 1a-c). In addition to the bright singlet-exciton peak (X), the phonon sideband of the Kmomentum dark exciton is clearly visible at a nearly chirality independent shift of ~130 meV [17,19].…”

“…, a value which corresponds to a few (1 to 2) excitons present on average in a diffusion length (100-200 nm, after taking account an exciton lifetime of  100ps [5,18]). This strongly indicates that the third carrier constituting the trion comes from a process of exciton-exciton interaction resulting in the annihilation of one exciton and the dissociation of the second one (see proposed mechanism on fig 3e).…”

New Route to Fluorescent Single-Walled Carbon Nanotube/Silica Nanocomposites: Balancing Fluorescence Intensity and Environmental Sensitivity

“…11,12 A number of surfactant systems have been used in attempts to optimize the photoluminescence intensity signal from dispersed SWNTs. 3,[13][14][15][16] Ideally, for imaging and sensing applications a higher PL signal would increase the signal-to-noise ratio resulting in increased sensitivity, ultimately down to the single molecule sensitivity. 17 Recent work 15 has…”

Synthesis and Photophysical Properties of C3‐Symmetric Star‐Shaped Molecules Containing Heterocycles: A New Tactics for Multiple Fischer Indolization

“…Further detail about the instrument is available elsewhere. [21] The lifetime values were obtained by fitting the fluorescence decays to multiexponential functions [22] by an iterative reconvolution technique using reduced c 2 as the parameter for goodness of fit (c 2 < 1.2 for a good fit). The fitting function is as follows:…”