Influence of quantum dot concentration on Förster resonant energy transfer in monodispersed nanocrystal quantum dot monolayers

Lunz, Manuela; Bradley, A. Louise; Chen, Wei-Yu; Gérard, Valérie; Byrne, Stephen J.; Gun’ko, Yurii K.; Lesnyak, Vladimir; Gaponik, Nikolai

doi:10.1103/physrevb.81.205316

Cited by 93 publications

(116 citation statements)

References 56 publications

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“…2. It is known, that FRET modifies the spectral dependences of the emission dynamics [28][29][30][31]. A similar behavior has been also found for the studied sample and will be reported elsewhere [32].…”

Section: Resultssupporting

confidence: 86%

Exciton spin dynamics of colloidal CdTe nanocrystals in magnetic fields

et al. 2014

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The recombination and spin dynamics of excitons in colloidal CdTe nanocrystals (NCs) are studied by time-resolved photoluminescence in high magnetic fields up to 15 T and at cryogenic temperatures. The recombination decay shows a nonexponential temporal behavior, with the longest component corresponding to the dark excitons having 260 ns decay time at zero magnetic field and 4.2 K temperature. This long component shortens to 150 ns at 15 T due to the magnetic-fieldinduced mixing of the bright and dark exciton states. The spin dynamics, assessed through the evolution of the magnetic-field-induced circular polarization degree of the photoluminescence, has a fast component shorter than 1 ns related to the bright excitons and a slow component of 5-10 ns associated with the dark excitons. The latter shortens with increasing magnetic field, which is characteristic for a phonon-assisted spin relaxation mechanism. The relatively low saturation level of the associated magnetic-field-induced circular polarization degree of −30% is explained by a model that suggests the CdTe NCs to constitute an ensemble of prolate and oblate NCs, both having a structural quantization axis. The exciton g-factor of 2.4-2.9 evaluated from fitting the experimental data in the frame of the suggested approach is in good agreement with the expected value for the dark excitons in CdTe NCs.

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Section: Resultssupporting

confidence: 86%

Exciton spin dynamics of colloidal CdTe nanocrystals in magnetic fields

et al. 2014

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“…Kagan et al were the first to report on FRET in QD solids. 28,29 Since then, FRET in QD systems has been studied in combination with organic dyes in solution-based complexes 19,30 and layer structures 31,32 as well as in pure QD assemblies such as clusters in solution, [33][34][35] monodispersed QD structures, [36][37][38] mixed donor-acceptor QD solids, 37,39 mixed donor-acceptor monolayers, 40,41 and donor-acceptor bilayer structures. 36,37,[42][43][44][45][46] The separated donor-acceptor bilayer structure is most interesting in terms of applications as it can be used in graded energy structures 22,23,47 and it also is the geometry used in substrate-based sensing platforms (see examples in the review by Borisov and Wolfbeis 5 ).…”

Section: Introductionmentioning

confidence: 99%

Concentration dependence of Förster resonant energy transfer between donor and acceptor nanocrystal quantum dot layers: Effect of donor-donor interactions

et al. 2011

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The influences of donor and acceptor concentrations on Förster resonant energy transfer (FRET) in a separated donor-acceptor quantum dot bilayer structure have been investigated. Donor intra-ensemble energy transfer is shown to have an impact on the donor-acceptor FRET efficiency in the bilayer structure. At high donor concentrations the FRET distance dependence and the acceptor concentration dependence in the separated donor-acceptor layer structure agree well with theories developed for FRET between randomly distributed, homogeneous donor and acceptor ensembles. However, discrepancies between measurement and theory are found at low donor concentrations. A donor concentration study shows that the FRET efficiency decreases with increasing donor concentration even though a donor concentration-independent FRET efficiency is predicted by standard theory. The observed dependence of the FRET efficiency on the donor concentration can be explained within the FRET rate model, for a constant, donor concentration independent FRET rate, by taking into account the concentration dependent donor reference lifetime arising from intra-donor ensemble FRET. This shows that the decrease in the FRET efficiency with increasing donor concentration is not a signature of a change in the donor-acceptor FRET rate, but due to the competition of the donor-acceptor and donor-donor energy transfer for the higher energy donors. As the intra-donor ensemble FRET represents another decay mechanism, the donor quantum yield for the higher energy donors decreases with increasing donor quantum dot (QD) concentration, as can also be seen from the redshift of the donor emission spectrum. Using this concentration dependent donor quantum yield in the calculation of the Förster radius, the FRET theory for homogeneous donor and acceptor ensembles can be modified to include the effect of the donor intra-ensemble transfer and to correctly describe the trends and absolute values of the measured FRET efficiencies as a function of the donor and the acceptor concentrations. These results show that in QD systems where intra-donor ensemble FRET is as important as the radiative and nonradiative donor decay mechanisms, the FRET rate rather than the FRET efficiency more appropriately characterizes the donor-acceptor FRET. By fitting with the rate model, FRET rates as high as (1.2 ns) −1 have been determined for the structures presented here.

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“…With increasing donor QD concentration c Don -corresponding to a decreasing QD separationa shortening of the decays is observed. This indicates that energy is transferred from the smaller QDs emitting on the blue side to larger QDs by the FRET mechanism [9]. The decrease of the corresponding lifetimes τ blue , obtained from a two-exponential fit of the PL decays, with increasing concentration c Don can be fitted by the theory of FRET in two dimensions [13], that has already been applied to characterize FRET in mixed donoracceptor monolayers [12].…”

Section: Monodispersed Quantum Dot Monolayersmentioning

confidence: 93%

“…2a, the theoretically calculated trend for the FRET efficiency in a two dimensions structure is also presented and it explains well the increasing FRET efficiency with donor QD concentration. Details about the fitting can be found elsewhere [9]. This shows that the process causing the concentration dependence of the optical properties in monodispersed QD structures, such as the peak emission wavelength and the PL lifetime, is dominated by FRET.…”

Section: Monodispersed Quantum Dot Monolayersmentioning

confidence: 97%

“…Then, the properties of QD monolayers prepared from eleven different green-emitting CdTe QDs are compared at one concentration. The QD concentration and the self-overlap of the spectral features of the QD ensemble both influence the intra-ensemble process significantly [9]. As an example, a donor/acceptor QD bilayer structure is investigated to highlight the impact of intra-donor ensemble FRET on the FRET efficiency in this structure and therefore, in more general terms, on the performance of QD based devices.…”

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confidence: 99%

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Influence of intra-ensemble energy transfer on the properties of nanocrystal quantum dot structures and devices

Lunz

Bradley

Chen

et al. 2010

2010 12th International Conference on Transparent Optical Networks

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The impact of intra-ensemble Förster resonant energy transfer (FRET) on the optical properties of monodispersed quantum dot (QD) monolayers and a donor/acceptor FRET bilayer structure are presented. The QD structures are characterized by steady-state absorption and photoluminescence (PL) spectroscopy as well as time-resolved PL measurements. The optical properties of the monodispersed monolayers, such as peak emission wavelength and PL decays, are strongly influenced by FRET from smaller to larger QDs within the ensemble. Comparing several QD samples, the spectral overlap of the QD ensemble and the QD concentration were identified as parameters that allow for tuning of FRET in monodispersed QD structures.For the donor/acceptor QD bilayer structure an unexpected decrease of the FRET efficiency between donor and acceptor layers is observed with increasing donor QD concentration. The concentration-dependent donor lifetime and a constant donor-acceptor FRET rate can explain this decrease within the FRET rate model. Even though the donor-acceptor FRET rate is donor-concentration independent -as expected from theory -its competition with donor-donor energy transfer leads to a concentration dependence of the FRET efficiency from donors to acceptors. This shows that intra-ensemble FRET can have an important impact on device performance. Keywords: Förster resonant energy transfer, colloidal quantum dots, photoluminescence spectroscopy, timeresolved emission decay, inhomogeneous broadening, spectral overlap. . In closely packed, monodispersed nanocrystal QD structures energy transfer between QDs can occur based on the overlap of emitting and absorbing states of QDs with different sizes, which is due to the inhomogeneous broadening of the QD ensemble and the Stokes shift between QD absorption and emission peak. This intra-ensemble energy transfer has been observed in QD solids [5,6] and layers [7] for CdSe as well as PbS QDs, that have been suggested for applications in the visible and infrared wavelength region respectively. It is important to investigate energy transfer within monodispersed QD structures more closely in order to identify ways to control intra-ensemble energy transfer other than by temperature tuning [6]. INTRODUCTIONHere we analyse the intra-ensemble energy transfer in monodispersed CdTe QD monolayers in detail for one QD sample and show that it is dominated by the Förster resonant energy transfer (FRET) mechanism [8]. Then, the properties of QD monolayers prepared from eleven different green-emitting CdTe QDs are compared at one concentration. The QD concentration and the self-overlap of the spectral features of the QD ensemble both influence the intra-ensemble process significantly [9]. As an example, a donor/acceptor QD bilayer structure is investigated to highlight the impact of intra-donor ensemble FRET on the FRET efficiency in this structure and therefore, in more general terms, on the performance of QD based devices.

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Influence of quantum dot concentration on Förster resonant energy transfer in monodispersed nanocrystal quantum dot monolayers

Cited by 93 publications

References 56 publications

Exciton spin dynamics of colloidal CdTe nanocrystals in magnetic fields

Exciton spin dynamics of colloidal CdTe nanocrystals in magnetic fields

Concentration dependence of Förster resonant energy transfer between donor and acceptor nanocrystal quantum dot layers: Effect of donor-donor interactions

Influence of intra-ensemble energy transfer on the properties of nanocrystal quantum dot structures and devices

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