Theory of Single-Molecule Optical Line-Shape Distributions in Low-Temperature Glasses

and, Eitan Geva; Skinner, James

doi:10.1021/jp971722o

Cited by 161 publications

(194 citation statements)

References 138 publications

(288 reference statements)

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“…Physical constants have been chosen to correspond with typical situations for a glassy material [14,55]. In order to compare with our previous work on stochastic models, it is necessary to map the above quantum description to a stochastic picture.…”

Section: B Numerical Resultsmentioning

confidence: 99%

“…Where C is a collection of constants incorporating the coupling strength between TLS and bath, which is typically taken as a parameter used to fit experiment rather than estimated from first principles [14]. Of course the top two lines just express the phonon assisted transition rates from state d to c and b to a as expected.…”

Section: Chromophore Coupled To a Two Level Systemmentioning

confidence: 99%

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Single Molecule Photon Counting Statistics for Quantum Mechanical Chromophore Dynamics

2006

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We extend the generating function technique for calculation of single molecule photon emission statistics [Y. Zheng and F. L. H. Brown, Phys. Rev. Lett., 90,238305 (2003)] to systems governed by multi-level quantum dynamics. This opens up the possibility to study phenomena that are outside the realm of purely stochastic and mixed quantum-stochastic models. In particular, the present methodology allows for calculation of photon statistics that are spectrally resolved and subject to quantum coherence. Several model calculations illustrate the generality of the technique and highlight quantitative and qualitative differences between quantum mechanical models and related stochastic approximations. Calculations suggest that studying photon statistics as a function of photon frequency has the potential to reveal more about system dynamics than the usual broadband detection schemes.

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Section: B Numerical Resultsmentioning

confidence: 99%

Section: Chromophore Coupled To a Two Level Systemmentioning

confidence: 99%

Single Molecule Photon Counting Statistics for Quantum Mechanical Chromophore Dynamics

2006

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“…28,29 While the mechanism of spectral diffusion is thought to be quite different in single QDs than in single molecules, a similar theory has been proposed to account for the observed line shape differences in the case of single nanocrystallite QDs. 9 However, while spectral diffusion has been observed in single nanocrystallites, only indirect evidence exists regarding its contribution to single dot line shapes.…”

mentioning

confidence: 99%

“…29 The fluctuating electric fields responsible for spectral diffusion in CdSe nanocrystallites are thought to result from the presence of charge carriers trapped on or near the surface of individual QDs 12 that result from ionization of the CdSe core. 6,32 In what follows, we speculate that spectral diffusion in single nanocrystallite QDs can be described in terms of point charges in a system of many welled potentials (trap sites).…”

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confidence: 99%

Influence of Spectral Diffusion on the Line Shapes of Single CdSe Nanocrystallite Quantum Dots

1999

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We study the emission line shapes of single CdSe nanocrystallite quantum dots. Single dot line shapes are found to result from rapid spectral shifting of the emission spectrum rather than the intrinsic physics of the quantum dot. A strong dependence of single dot line widths on excitation intensity, wavelength, temperature, and integration time is found and is correlated with the number of times that the quantum dot is excited during the acquisition of a single spectrum. The observed results are consistent with thermally assisted spectral diffusion, activated by the release of excess excitation energy.Recent advances in the detection of single molecules have been responsible for a level of understanding in condensed phase systems that was not previously possible. Of particular interest are incoherent dynamic effects, which can be completely hidden when averaged over an ensemble. In recent years, single chromophore spectroscopy has allowed the direct observation of single enzyme reactions, 1 single energy transfer events, 2 and single molecule rotational dynamics. 3 In addition, new and unexpected physical phenomena have been observed, which appear to be common to many single chromophore systems, such as fluorescence blinking 4-6 and spectral shifting (spectral diffusion). [7][8][9][10][11][12] One field that has greatly benefited from single chromophore spectroscopy is the study of semiconductor quantum dots (QDs). QDs are of great interest due to their unique size dependent optical properties, 13 which can easily be tuned during fabrication. 14 Unfortunately, the characteristics that make QDs interesting also make them inherently difficult to study. Inhomogeneities in size and shape within ensemble samples result in spectral broadening that is many orders of magnitude larger than single QD spectra. 9,15 Though the mechanisms are thought to be quite different, the study of single QDs has revealed phenomena common to other single chromophore systems such as blinking 4 and spectral diffusion. [9][10][11][12] It has also revealed new characteristics specific to QDs such as ultranarrow transition line widths, 9,15 giant Overhauser shifts, 16 multicarrier effects, 17,18 and fluctuating local electric fields. 12 One area of particular interest which can, in principle, be addressed on the single QD level, is the nature of the homogeneous line shape. While theory predicts that QDs should have atomic-like spectral transitions due to long excited-state lifetimes and weak coupling to acoustic phonons, 19 previous ensemble experiments have suggested that line widths in both excitation [20][21][22] and emission 23-25 are quite broad (for example, "homogeneous" line widths extracted from fluorescence line narrowing experiments in CdSe nanocrystallite QDs are reported to be ∼5 meV 26 ). It was expected that single QD spectroscopy would uncover the true "homogeneous" line width. However, while single dot line widths are typically found to be significantly narrower than what is seen in ensemble experiments, many single dot exp...

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“…Unfortunately, optical measurements provide only the product mc TLS . However, the value of c TLS can be estimated on the basis of specific heat data [27]. Following this procedure a value of ͗m͘ ഠ 11 GHz ?…”

mentioning

confidence: 99%

Electronic Energy Relaxation and Transition Frequency Jumps of Single Molecules at 30 mK

Plakhotnik

Donley²,

Kharlamov³

2001

Phys. Rev. Lett.

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Transition frequency jumps for single terrylene molecules in a polyethylene matrix caused by resonant laser irradiation are investigated at 30 mK. These jumps are not accompanied by substantial sample heating. A model for the effect is proposed, based on the interaction of tunneling two-level systems (TLSs) surrounding the single molecule with high-energy nonthermal phonons emitted by the molecule during electronic energy relaxation. The radius of the effective interaction volume is estimated to be r m ഠ 12.5 nm, and the interaction cross section for nonequilibrium phonon -TLS scattering is estimated as ϳ10 222 cm 2 . DOI: 10.1103/PhysRevLett.87.015504 PACS numbers: 61.43.Fs, 78.40. -q The low-temperature properties of glasses have strong anomalies as compared to crystals [1][2][3]. These anomalies are successfully described by the tunneling two-level system (TLS) model, which assumes the existence of a special kind of local low-energy excitations with a very broad distribution of energies and relaxation rates. Phonon assisted TLS dynamics is thought to be responsible for many anomalous properties of glasses at low temperatures and has been the subject of extensive investigation by various methods for almost 30 years. One tool used for the investigation of these dynamics is optical spectroscopy, in particular, photon echo, hole burning, and single-molecule spectroscopy (SMS) (see reviews [4 -13]). All of these methods use a chromophore impurity as a probe whose resonance frequency is subject to spectral diffusion (SD) because of interactions between the probe and TLSs. In principle, impurities can disturb the matrix structure, but there is no indication that impurities at low and moderate concentrations affect the TLS density. An increase of the rate of SD has been detected in samples only at chromophore concentrations above 10 22 mol͞l [14]. Another expected effect of impurity molecules on their local environments could arise from light absorbed by the chromophore. Through subsequent decay processes the absorbed energy is inevitably partially converted to high-energy phonons, which spread into the surrounding space, exciting TLSs and finally decaying into thermal equilibrium phonons. TLS excitation via high-energy phonons was suggested in [14] as a reason for a specific SD time dependence in highly concentrated samples, but no direct evidence for this effect was obtained. The advantage of SMS in measurements of such a kind is that one and the same molecule serves as a phonon generator and as a probe. Therefore, the measurements can be carried out at a low concentration of chromophores, which does not disturb the structure of the matrix. The present work is a first attempt at direct investigation of the influence of highenergy phonons emitted by impurity molecules on their local environments.Experiments were performed on the sample used in previous works [15,16]. The sample has a sandwich structure. A thin layer (about 1 mm thick) of polyethylene (PE) doped with terrylene at a concentration of ϳ10 26 M was p...

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Theory of Single-Molecule Optical Line-Shape Distributions in Low-Temperature Glasses

Cited by 161 publications

References 138 publications

Single Molecule Photon Counting Statistics for Quantum Mechanical Chromophore Dynamics

Single Molecule Photon Counting Statistics for Quantum Mechanical Chromophore Dynamics

Influence of Spectral Diffusion on the Line Shapes of Single CdSe Nanocrystallite Quantum Dots

Electronic Energy Relaxation and Transition Frequency Jumps of Single Molecules at 30 mK

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