Exponential Decay Lifetimes of Excitons in Individual Single-Walled Carbon Nanotubes

Hagen, Axel; Steiner, M.; Raschke, Markus B.; Lienau, Christoph; Hertel, Tobias; Qian, Huihong; Meixner, Alfred J.; Hartschuh, Achim

doi:10.1103/physrevlett.95.197401

Cited by 213 publications

(256 citation statements)

References 25 publications

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“…233 Second, the local environment strongly influences the measured line widths and photoluminescent lifetimes of SWNTs in an unknown manner. 209,234 As presented in Chapter 3, fluorescence peaks shift and line widths sharpen or broaden according to the dispersing agent associated with the SWNT. The local environment also encompasses defect trap sites along the sidewall that alter the excited state lifetimes for individual nanotubes.…”

Section: Current Challenges In Swnt Photophysicsmentioning

confidence: 96%

“…The local environment also encompasses defect trap sites along the sidewall that alter the excited state lifetimes for individual nanotubes. 234 To better understand these effects, single molecule fluorescence and photoluminescence lifetime measurements could be conducted for SWNTs suspended in a range of surfactants. In particular, near-field optical techniques could enable the study of tiny areas of the SWNT with a uniform micellar environment (i.e., molecules typically adsorb nonuniformly onto the SWNT sidewall, and far-field measurements average over this distribution of local dielectric environments).…”

Section: Current Challenges In Swnt Photophysicsmentioning

confidence: 99%

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Photophysics of Individual Single-Walled Carbon Nanotubes

2008

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Single-walled carbon nanotubes (SWNTs) are cylindrical graphitic molecules that have remained at the forefront of nanomaterials research since 1991, largely due to their exceptional and unusual mechanical, electrical, and optical properties. The motivation for understanding how nanotubes interact with light (i.e., SWNT photophysics) is both fundamental and applied. Individual nanotubes may someday be used as superior near-infrared fluorophores, biological tags and sensors, and components for ultrahigh-speed optical communications systems. Establishing an understanding of basic nanotube photophysics is intrinsically significant and should enable the rapid development of such innovations. Unlike conventional molecules, carbon nanotubes are synthesized as heterogeneous samples, composed of molecules with different diameters, chiralities, and lengths. Because a nanotube can be either metallic or semiconducting depending on its particular molecular structure, SWNT samples are also mixtures of conductors and semiconductors. Early progress in understanding the optical characteristics of SWNTs was limited because nanotubes aggregate when synthesized, causing a mixing of the energy states of different nanotube structures. Recently, significant improvements in sample preparation have made it possible to isolate individual nanotubes, enabling many advances in characterizing their optical properties. In this Account, single-molecule confocal microscopy and spectroscopy were implemented to study the fluorescence from individual nanotubes. Single-molecule measurements naturally circumvent the difficulties associated with SWNT sample inhomogeneities. Intrinsic SWNT photoluminescence has a simple narrow Lorentzian line shape and a polarization dependence, as expected for a one-dimensional system. Although the local environment heavily influences the optical transition wavelength and intensity, single nanotubes are exceptionally photostable. In fact, they have the unique characteristic that their single molecule fluorescence intensity remains constant over time; SWNTs do not “blink” or photobleach under ambient conditions. In addition, transient absorption spectroscopy was used to examine the relaxation dynamics of photoexcited nanotubes and to elucidate the nature of the SWNT excited state. For metallic SWNTs, very fast initial recovery times (300–500 fs) corresponded to excited-state relaxation. For semiconducting SWNTs, an additional slower decay component was observed (50–100 ps) that corresponded to electron–hole recombination. As the excitation intensity was increased, multiple electron–hole pairs were generated in the SWNT; however, these e−h pairs annihilated each other completely in under 3 ps. Studying the dynamics of this annihilation process revealed the lifetimes for one, two, and three e−h pairs, which further confirmed that the photoexcitation of SWNTs produces not free electrons but rather one-dimensional bound electron–hole pairs (i.e., excitons). In summary, nanotube photophysics is a rapidly developing area o...

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Section: Current Challenges In Swnt Photophysicsmentioning

confidence: 96%

Section: Current Challenges In Swnt Photophysicsmentioning

confidence: 99%

Photophysics of Individual Single-Walled Carbon Nanotubes

2008

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“…We found a strong red shift caused by DNA-wrapping of between 7 and 17 meV depending on the nanotube chirality. In the next step, TENOM was used to resolve PL variations along DNA-wrapped (6,5) and (6,4) nanotubes. Here two distinct emission bands are identified and assigned to emission from DNA-wrapped segments of the nanotube at E DNA and unwrapped segments at E 0 , distinguished by energy shifts of 18 meV for (6,5) and 30 meV for (6,4)-nanotubes, respectively.…”

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confidence: 99%

“…Figure 2 presents the near-field PL measurement of a DNA-wrapped CoMoCAT (6,5) SWNT spin-coated on mica. Figure 2b represents the integrated intensity from 970 to 1030 nm covering the emission range of (6,5) nanotubes. 7 First, the center emission energies were obtained by fitting the spectra with a single Lorentzian line shape function shown in Figure 2c and d. Apparently, the emission energy varies between 1.259 and 1.241 eV along the nanotube, as indicated by the two red dashed lines in Figure 2c, while the average of all near-field spectra at 1.249 eV coincides with the value from confocal far-field measurements.…”

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Visualizing the Local Optical Response of Semiconducting Carbon Nanotubes to DNA-Wrapping

et al. 2008

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We studied the local optical response of semiconducting single-walled carbon nanotubes to wrapping by DNA segments using high resolution tip-enhanced near-field microscopy. Photoluminescence (PL) near-field images of single nanotubes reveal large DNA-wrapping-induced red shifts of the exciton energy that are two times higher than indicated by spatially averaging confocal microscopy. Near-field PL spectra taken along nanotubes feature two distinct PL bands resulting from DNA-wrapped and unwrapped nanotube segments. The transition between the two energy levels occurs on a length scale smaller than our spatial resolution of about 15 nm.Semiconducting single-walled carbon nanotubes (SWNTs) as photoluminescent quasi-one-dimensional systems have attracted enormous scientific interest and have large potential for various applications in photonics and opto-and nanoelectronics. 1-3 Photoluminescence (PL) of nanotubes results from exciton recombination and occurs in the near-infrared spectral range with emission energies controlled mainly by the nanotube structure (n,m). [4][5][6][7][8] Since nanotubes consist of surface atoms only, the detected emission energy is very sensitive to the nanotube environment, making them promising candidates for sensing applications. 9 At present, the influence of the environment is described by its relative dielectric constant ε influencing exciton binding energies but also renormalizing the band gap through charge carrier screening. 10-14 As a result, the emission energy of nanotubes is modulated by the dielectric constant, which can be expected to be nonuniform along nanotubes, leading to nonuniform emission energies in single nanotube measurements. 8,15,16 The use of DNA for hybridization of carbon nanotube sidewalls has facilitated sorting nanotubes and building chemical sensors. 9,[17][18][19] Single-strand DNA-wrapping introduces DNA segments with finite length, while the details of the secondary DNA structure will be determined by a complex interplay between π-π stacking interactions between DNA bases and nanotube surface as well as electrostatic interactions of the phosphate backbone. [20][21][22] The effect of helical wrapping by the charged DNA backbone was modeled by applying a helical potential causing symmetry breaking of the nanotube electronic structure and small energetic shifts for semiconducting nanotubes (0.01 meV in water). 23,24 It is well-known that DNA-wrapping red-shifts the PL energy depending on the nanotube chirality by several tens of meV compared to the values reported for micelleencapsulated nanotubes in aqueous solution, 7,25,26 which can be attributed to an increasing ε. 14 The surface coverage with DNA segments of finite length is expected to result in a nonuniform dielectric environment along the nanotubes. 25 Limited by diffraction, the PL information collected in confocal microscopy contains the optical response from a nanotube length of about 300 nm, which is far too large to clarify details of individual DNA-nanotube interactions. Tipenhanced n...

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“…Being first synthesised as a by-product of fullerene production [39], CNTs have gained high attractiveness for novel electronics and photonics device development due to their unique features [40]. In 2003, single-walled CNTs (SWNTs) were applied in Erdoped fibre laser for passive mode locking for the first time [41]. SWNTs are a promising candidate for the ultrashort pulse generation because they possess ultrafast excited state carrier dynamic and high optical nonlinearity [42][43][44].…”

Section: Introductionmentioning

confidence: 99%

Carbon nanotubes for ultrafast fibre lasers

et al. 2016

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Carbon nanotubes (CNTs) possess both remarkable optical properties and high potential for integration in various photonic devices. We overview, here, recent progress in CNT applications in fibre optics putting particular emphasis on fibre lasers. We discuss fabrication and characterisation of different CNTs, development of CNTbased saturable absorbers (CNT-SA), their integration and operation in fibre laser cavities putting emphasis on stateof-the-art fibre lasers, mode locked using CNT-SA. We discuss new design concepts of high-performance ultrafast operation fibre lasers covering ytterbium (Yb), bismuth (Bi), erbium (Er), thulium (Tm) and holmium (Ho)-doped fibre lasers.

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Exponential Decay Lifetimes of Excitons in Individual Single-Walled Carbon Nanotubes

Cited by 213 publications

References 25 publications

Photophysics of Individual Single-Walled Carbon Nanotubes

Photophysics of Individual Single-Walled Carbon Nanotubes

Visualizing the Local Optical Response of Semiconducting Carbon Nanotubes to DNA-Wrapping

Carbon nanotubes for ultrafast fibre lasers

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