Homogeneous linewidth of confined electron-hole-pair states in II-VI quantum dots

Woggon, U.; Гапоненко, С. В.; Langbein, Wolfgang Werner; Uhrig, A.; Klingshirn, C.

doi:10.1103/physrevb.47.3684

Cited by 100 publications

(36 citation statements)

References 29 publications

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“…4, 5,6,7,8,9 However, the issue is still open since none of these techniques is applicable to the whole variety of inhomogeneous physical systems of interest. For instance, in amorphous solids site-selective spectroscopy can been successfully applied only to defects which allow the the direct observation of the zero phonon line (ZPL) by virtue of a weak coupling with the vibrational modes of the matrix.…”

Section: Introductionmentioning

confidence: 99%

Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time-resolved emission spectroscopy

et al. 2008

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The article describes an experimental method that allows to estimate the inhomogeneous and homogeneous linewidths of the photoluminescence band of a point defect in an amorphous solid. We performed low temperature time-resolved luminescence measurements on two defects chosen as model systems for our analysis: extrinsic Oxygen Deficient Centers (ODC(II)) in amorphous silica and F + 3 centers in crystalline Lithium Fluoride. Measurements evidence that only defects embedded in the amorphous matrix feature a dependence of the radiative decay lifetime on the emission energy and a time dependence of the first moment of the emission band. A theoretical model is developed to link these properties to the structural disorder typical of amorphous solids. Specifically, the observations on ODC(II) are interpreted by introducing a gaussian statistical distribution of the zero phonon line energy position. Comparison with the results obtained on F + 3 crystalline defects strongly confirms the validity of the model. By analyzing experimental data within this frame, we obtain separate estimations of the homogenous and inhomogeneous contributions to the measured total linewidth of ODC(II), which results to be mostly inhomogeneous.

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Section: Introductionmentioning

confidence: 99%

Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time-resolved emission spectroscopy

et al. 2008

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“…This latter effect is observed as "photodarkening" by strong laser illumination which leads to a weak broadband reduction of the linear transmission [15,21] and to drastically reduced lifetimes of optically excited carriers, resulting in a reduction of the luminescence First publ. in: Applied Physics B 62 (1996) intensity and of the carrier-induced absorption changes in the nanosecond time regime [16,[21][22][23]. Also, a large amount of theoretical work has been done using various refinements of the first effective-mass calculations [3,24,25] in order to understand the optical properties of semiconductor NCs [26-30, 8, 31].…”

Section: Pacsmentioning

confidence: 99%

“…The magnitude and the dynamics of the optical nonlinearities have been investigated with various experimental techniques, such as single-beam absorption saturation, [15] pump-probe measurements in the nanosecond, [4,6,7,9,10,16] picosecond, [5,17,18] and femtosecond regime, [4,19] and photon-echo experiments [11,14,20].…”

Section: Pacsmentioning

confidence: 99%

Ultrafast dynamics of carrier-induced absorption changes in highly-excited CdSe nanocrystals

et al. 1996

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Abstract. We use femtosecond time-resolved transmission spectroscopy to study the density and time dependence of transient absorption changes of CdSe nanocrystals. Our data show pronounced absorption saturation up to complete bleaching of the lowest optical transition. At high carrier density the nonlinear spectra show several peaks that can be related to the two lowest quantized electron states. Thetime dependence of the carrier-induced absorption changes indicates an ultrafast relaxation process within the strongly broadened absorption lines. 78.47.+p; 73.20.Dx; 71.35.+z In recent years, there has been a strong interest in lowdimensional semiconductor structures such as quantum wells, quantum wires, and quantum dots. The electronic states in these artificial materials are strongly influenced by size quantization effects, which occur when the dimensions of the structures become comparable to or smaller than the exciton Bohr radius aB. Then, the electronic and optical properties of the structures become determined by their geometry. Thus, the controlled fabrication of low-dimensional semiconductor structures may allow to obtain materials with predefined properties. PACS:In addition, size quantization has been shown to lead to a significant enhancement of excitonic effects and to strongly enhanced optical nonlinearities in two-dimensional quantum wells, where the carriers are confined in only one dimension [1]. It can be expected that a confinement of carriers in two or three dimensions will lead to a further enhancement of the optical nonlinearities. Therefore, semiconductor quantum dots appear as a promising new material for nonlinear optical applications. It has been found that semiconductor crystallites with radii on the order of a few nanometer, denoted as nanocrystals (NCs), can be rather easily produced in semiconductor-doped glasses (which are commercially available as color-glass filters) or in organic solution [2][3][4]. The linear absorption of such samples generally shows a correlation with the average NC size, as the lowest absorption feature shifts towards higher energies with decreasing size [3,[5][6][7][8][9][10][11]. While this clear sign of size quantization is easily observed, the absorption spectra of semiconductordoped glasses usually fail to show sharp exciton peaks (in contrast with two-dimensional quantum wells) or even wellseparated absorption lines that reflect the expected discrete energy spectrum of a "zero-dimensional" structure. It is commonly accepted that the presence of discrete electronic states is masked in the linear absorption by strong homogeneous and inhomogeneous broadening. The nanocrystals may vary in size, geometry, and chemical composition. These variations cause a strong inhomogeneous broadening of the optical transitions. Variations of the NC size are typically on the order of 25% [12]. This value may be reduced to a few percent by sophisticated preparation techniques, but even then the size distribution has a significant influence on the optical properties [4,10,1...

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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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Homogeneous linewidth of confined electron-hole-pair states in II-VI quantum dots

Cited by 100 publications

References 29 publications

Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time-resolved emission spectroscopy

Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time-resolved emission spectroscopy

Ultrafast dynamics of carrier-induced absorption changes in highly-excited CdSe nanocrystals

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

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