Quantum size dependence of femtosecond electronic dephasing and vibrational dynamics in CdSe nanocrystals

Mittleman, Daniel M.; Schoenlein, R. W.; Shiang, J. J.; Colvin, Vicki L.; Alivisatos, A. Paul; Shank, C. V.

doi:10.1103/physrevb.49.14435

Cited by 306 publications

(296 citation statements)

References 89 publications

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“…The signal decayed as exp(−4τ /T 2 ) with T 2 ∼ 440f s. From the measured dephasing time T 2 a homogeneous linewidth of ∼ 3 meV can be obtained, in agreement with previous measurements 13 . Low energy acoustic phonons can efficiently scatter excitons in the highly degenerate spin states within the manifold in PbS quantum dots and are generally thought to be the mechanism behind the rapid dephasing in colloidal quantum dots [13][14][15][16][17][18] .…”

Section: Resultsmentioning

confidence: 99%

Quantum beats due to excitonic ground-state splitting in colloidal quantum dots

et al. 2012

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The dephasing of PbS quantum dots has been carefully measured using three pulse four-wave mixing and two-dimensional nonlinear optical spectroscopy. The temperature dependence of the homogeneous linewidth obtained from the two-dimensional spectra indicates significant scattering by acoustic phonons, whereas the excitation density dependence shows negligible excitation induced broadening in agreement with previous results. The rapid dephasing is attributed to elastic scattering by acoustic phonons. However, two dephasing components emerge, the short component that dominates the decay and a weaker longer decay, likely due to 'zero-phonon' dephasing. Quantum beats originating from two separate states can be observed, possibly revealing a ∼23.6 meV splitting of the excitonic ground state. Finally, the emergence of biexcitonic effects enhanced by the high quantum confinement is discussed.

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Section: Resultsmentioning

confidence: 99%

Quantum beats due to excitonic ground-state splitting in colloidal quantum dots

et al. 2012

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“…Resonant excitation of quantum dots in conjunction with strong electron-phonon coupling leads to a modulation of a four wave mixing signal with the frequency of the LO phonon in CdSe quantum dots 128,129] and of the LO and TO mode in InP quantum dots 131]. Coherent acoustic modes could be observed in resonant pump-probe experiments on PbS quantum dots 132,133].…”

Section: Recent Developmentsmentioning

confidence: 96%

“…Coherent optical and acoustic modes have been observed recently in semiconductor quantum dots 128,129,130,131,132]. Resonant excitation of quantum dots in conjunction with strong electron-phonon coupling leads to a modulation of a four wave mixing signal with the frequency of the LO phonon in CdSe quantum dots 128,129] and of the LO and TO mode in InP quantum dots 131].…”

Section: Recent Developmentsmentioning

confidence: 99%

Coherent phonons in condensed media

Dekorsy¹,

Cho²,

Kurz³

2000

Topics in Applied Physics

139

127

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Abstract. The impulsive excitation and phase-sensitive detection of coherent phonons and phonon-polaritons provide a detailed insight i n to the dynamical properties of matter. The experiments are based on optical pump-probe techniques with femtosecond time resolution. These techniques enable the detection of amplitude and phase of the coherent lattice motion simultaneously. F requencies in the THz range and dephasing times in the picosecond range can be obtained with high accuracy. Especially in semiconductors and semiconductor heterostructures, where a coherent phonon mode and free carriers are excited simultaneously, important information about carrier-phonon interaction far away from equilibrium is obtained. This paper presents an overview of recent a c hievements in this vivid eld of condensed matter physics.

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“…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.…”

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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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Quantum size dependence of femtosecond electronic dephasing and vibrational dynamics in CdSe nanocrystals

Cited by 306 publications

References 89 publications

Quantum beats due to excitonic ground-state splitting in colloidal quantum dots

Quantum beats due to excitonic ground-state splitting in colloidal quantum dots

Coherent phonons in condensed media

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

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