Triplet State Absorption in Carbon Nanotubes:  A TD−DFT Study

Tretiak, Sergei

doi:10.1021/nl070355h

Cited by 85 publications

(124 citation statements)

References 38 publications

(216 reference statements)

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“…213,219 Another conjecture is that these processes may accelerate intersystem crossing to triplet states, which sequesters excited state carriers and lowers the observed QY. 220 Promisingly, SWNT sample quality is continuing to improve, and tailoring the environment immediately surrounding SWNTs could make it possible to suppress competing processes that arise from extrinsic factors, enabling more carriers to decay by radiative relaxation pathways.…”

Section: Motivationmentioning

confidence: 99%

“…Although the energy of the triplet state has been predicted for SWNTs, this transition has never been observed experimentally for ensemble samples. 220 At low temperatures, it may be possible to observe phosphorescence from the triplet state and to quantify the fraction of excited-state carriers involved in intersystem crossing.…”

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: Motivationmentioning

confidence: 99%

Section: Current Challenges In Swnt Photophysicsmentioning

confidence: 99%

Photophysics of Individual Single-Walled Carbon Nanotubes

2008

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“…It turns out to be d ¼ 3 AE 0.5 meV. This relatively small value (compared to theoretical predictions in the range of a few tens of meV [15,16]) means that the dark and bright states are almost equally populated at room temperature. Therefore, the existence of this dark state cannot in itself explain the very weak PL quantum yields reported for carbon nanotubes.…”

Section: Excitonsmentioning

confidence: 72%

“…Therefore, the existence of this dark state cannot in itself explain the very weak PL quantum yields reported for carbon nanotubes. In this context, the role of triplet states that are predicted to lie far below the singlet states [15] remains to be explored. This procedure can be repeated for other chiral species by means of selective PL.…”

Section: Excitonsmentioning

confidence: 99%

Excitonic signatures in the optical response of single‐wall carbon nanotubes

Voisin¹,

Berger²,

Berciaud³

et al. 2012

Physica Status Solidi (b)

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The optical properties of single-wall carbon nanotubes (SWNTs) are dominated by the excitonic character of the transitions even at room temperature. The very peculiar properties of these excitons arise from both the one-dimensional (1D) nature of carbon nanotubes and from the electronic properties of graphene from which nanotubes are made. We first propose a brief qualitative review of the structure of the excitonic manifold and emphasize the role of dark states. We describe recent experimental investigations of this excitonic structure by means of temperature dependent PL measurements. We investigate the case of upper sub-bands and show that high-order optical transitions remain excitonic for large diameter nanotubes. A careful investigation of Rayleigh scattering spectra at the single nanotube level reveals clear exciton-phonon side-bands and Lorentzian line profiles for all semi-conducting nanotubes. In contrast, metallic nanotubes show an ambivalent behavior which is related to the reduced excitonic binding energy.Schematic of the exciton manifold in single-wall carbon nanotubes.

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“…However, its role as a practical method to obtain dynamical properties of manybody systems is so far unrivaled by other ab initio methods due to the accuracy it provides with the currently available functionals versus the computational cost it entails. General prescriptions to compute excited state energies and their oscillator strengths via TDDFT have been reported, [9][10][11][12][13][14][15] and have been successfully used to study a wide variety of phenomena, such as chemical [16][17][18][19][20][21] and nonlinear optical [22][23][24] properties in nanomaterials, resonant energy transfer, 25,26 and many-body effects in solid state systems, [27][28][29] and lifetimes of atomic resonance states, 30,31 among many others. Whereas most of the studies so far have relied on the local density approximation, 1,[32][33][34] a big effort has also been taken on the direction of capturing memory effects.…”

mentioning

confidence: 99%

Remarks on time-dependent [current]-density functional theory for open quantum systems

Yuen-Zhou

Aspuru‐Guzik

2013

Phys. Chem. Chem. Phys.

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Time-dependent [current]-density functional theory for open quantum systems (OQS) has emerged as a formalism that can incorporate dissipative effects in the dynamics of many-body quantum systems.Here, we review and clarify some formal aspects of these theories that have been recently questioned in the literature. In particular, we provide theoretical support for the following conclusions: (1) contrary to what we and others had stated before, within the master equation framework, there is in fact a one-to-one mapping between vector potentials and current densities for fixed initial state, particleparticle interaction, and memory kernel; (2) regardless of the first conclusion, all of our recently suggested Kohn-Sham (KS) schemes to reproduce the current and particle densities of the original OQS, and in particular, the use of a KS closed driven system, remains formally valid; (3) the Lindblad master equation maintains the positivity of the density matrix regardless of the time-dependence of the Hamiltonian or the dissipation operators; (4) within the stochastic Schrödinger equation picture, a one-to-one mapping from stochastic vector potential to stochastic current density for individual trajectories has not been proven so far, except in the case where the vector potential is the same for every member of the ensemble, in which case, it reduces to the Lindblad master equation picture; (5) master equations may violate certain desired properties of the density matrix, such as positivity, but they remain as one of the most useful constructs to study OQS when the environment is not easily incorporated explicitly in the calculation. The conclusions support our previous work as formally rigorous, offer new insights into it, and provide a common ground to discuss related theories.

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Triplet State Absorption in Carbon Nanotubes: A TD−DFT Study

Cited by 85 publications

References 38 publications

Photophysics of Individual Single-Walled Carbon Nanotubes

Photophysics of Individual Single-Walled Carbon Nanotubes

Excitonic signatures in the optical response of single‐wall carbon nanotubes

Remarks on time-dependent [current]-density functional theory for open quantum systems

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