Recombination dynamics of luminescence in colloidal CdSe/ZnS quantum dots

Lee, W. Z.; Shu, G. W.; Wang, J. S.; Shen, Ji‐Lin; Lin, Cheng-An J.; Chang, Walter; Ruaan, Ruoh‐Chyu; Chou, Wu–Ching; Lu, Chung‐Hsin; Lee, Y. C.

doi:10.1088/0957-4484/16/9/018

Cited by 60 publications

(59 citation statements)

References 25 publications

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“…[38] Recombination via radiative traps will result in lingering luminescence. [48] Because the QDs are perfectly crystallized, as shown in Figures 4 and 5, the localized states are mainly on the QD surfaces. [37] It has been suggested that the energy levels of the radiative surface traps at CdSe QDs are near the band edge.…”

mentioning

confidence: 98%

Controlled Synthesis of CdSe Quantum Dots by a Microwave‐Enhanced Process: A Green Approach for Mass Production

Ayele

Chen

et al. 2011

Chemistry A European J

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A method that does not employ hot-injection techniques has been developed for the size-tunable synthesis of high-quality CdSe quantum dots (QDs) with zinc blende structure. In this environmentally benign synthetic route, which uses less toxic precursors, solvents, and capping ligands, CdSe QDs that absorb visible light are obtained. The size of the as-prepared CdSe QDs and thus their optical properties can be manipulated by changing the microwave reaction conditions. The QDs were characterized by XRD, TEM, UV/Vis, FTIR, time-resolved fluorescence spectroscopy, and fluorescence spectrophotometry. In this approach, the reaction is conducted in open air and at a much lower temperature than in hot-injection techniques. The use of microwaves in this process allows for a highly reproducible and effective synthesis protocol that is fully adaptable for mass production and can be easily employed to synthesize a variety of semiconductor QDs with the desired properties. Possible applications of the CdSe QDs were assessed by deposition on TiO(2) films.

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mentioning

confidence: 98%

Controlled Synthesis of CdSe Quantum Dots by a Microwave‐Enhanced Process: A Green Approach for Mass Production

Ayele

Chen

et al. 2011

Chemistry A European J

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“…Nonetheless, there are 2 major advantages of using PL to examine trap states: (i) the well documented (5-12) sensitivity of NC PL to interface and environmental changes and (ii) the ability of time-resolved PL measurements to resolve processes that occur over a large dynamic range of timescales. Several groups (11,(31)(32)(33)(34)(35)(36)(37) have studied the influence of trap states on PL transients in CdSe NCs, and stochastic models have been used in some of these studies to extract radiative decay rates or trapping rates. Although such models successfully reproduce exciton-only dynamics, they have been unable to capture satisfactorily the influence of interface states.…”

mentioning

confidence: 99%

Quantitative modeling of the role of surface traps in CdSe/CdS/ZnS nanocrystal photoluminescence decay dynamics

Jones

Scholes

2009

Proc. Natl. Acad. Sci. U.S.A.

325

381

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Charge carrier trapping is an important phenomenon in nanocrystal (NC) decay dynamics because it reduces photoluminescence (PL) quantum efficiencies and obscures efforts to understand the interaction of NC excitons with their surroundings. Particularly crucial to our understanding of excitation dynamics in, e.g., multiNC assemblies, would be a way of differentiating between processes involving trap states and those that do not. Direct optical measurement of NC trap state processes is not usually possible because they have negligible transition dipole moments; however, they are known to indirectly affect exciton photoluminescence. Here, we develop a framework, based on Marcus electron transfer theory, to determine NC trap state dynamics from time-resolved NC exciton PL measurements. Our results demonstrate the sensitivity of PL to interfacial dynamics, indicating that the technique can be used as an indirect but effective probe of trap distribution changes. We anticipate that this study represents a step toward understanding how excitons in nanocrystals interact with their surroundings: a quality that must be optimized for their efficient application in photovoltaics, photodetectors, or chemical sensors.quantum dot ͉ states ͉ electron transfer ͉ time-correlated single-photon counting ͉ fluorescence intermittency C olloidal semiconductor nanocrystals (NCs) are potentially useful in a variety of photoactive applications because of their widely tunable electronic band gaps and their ease of processability. Different from well-studied molecular fluorophores, the excited electronic states of NCs with diameters in the range 1 to 10 nm are examples of nanoscale excitons (1). To be used in solar photovoltaics, for example, photo-generated NC excitons must be able to dissociate and transfer charge carriers to their surroundings in a controlled fashion; however, this process is impeded in NCs by the considerable influence of surface-localized states that trap carriers (2). Perturbations due to traps are important because of the significant surface-to-volume ratios characteristic of small colloids (3, 4). Certain surface sites act as charge acceptors that dissociate excitons and therefore reduce the photoluminescence (PL) quantum yield. Changes in solvent or surface-bound coordinating ligands have been found to affect these surface traps and thereby influence steady-state (5-9) and time-resolved (10-12) NC PL. The ability of surface traps to act as charge acceptors makes them excellent model systems for elucidating exciton dissociation processes occurring on the NC surface. Properties intrinsic to NC excitons have been examined in detail (13-17) but comparatively little is understood about the interplay among intrinsic excitons and surface states. Here, we report investigations of CdSe/CdS/ZnS core/shell/shell NC ensemble PL and establish a quantitative model of interfacial trapping and its effect on NC PL dynamics.Colloidal CdSe NCs are coated with passivating ligands that sustain their dispersion in solution and minimize ...

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“…Again, the following discussion is based on the properties of CdSe and CdTe nanocrystals. Several relaxation processes have been proposed to explain the photophysics of CdSe QDs, including the thermally activated exciton transition from dark to bright states (Crooker et al, 2003) and carriers surface localization in trap states (Lee et al, 2005). Moreover, it has been shown that at room temperature the main non radiative process in CdSe/ZnS core/shell QDs is thermal escape, assisted by multiple longitudinal optical (LO) phonons absorption (Valerini et al, 2005), while at low temperature evidence for carrier trapping at surface defects was found.…”

Section: Excitation and Relaxation Processes In Colloidal Nanocrystalsmentioning

confidence: 99%

“…Despite these results, the role and the chemical origin (Wang et al, 2003b) of the surface defect states in the radiative and non radiative relaxation in nanocrystals has not been clarified completely. The existence of surface states due to unpassivated dangling bonds has been invoked to explain anomalous red-shifted emission bands in colloidal nanocrystals (Lee et al, 2005). On the contrary, it has been shown that above-gap trap states (Bawendi et al, 1992) affect the ultrafast relaxation dynamics (Cretì et al, 2005) and the single nanoparticle PL spectra of CdSe quantum rods (Rothenberg et al, 2005) due to charge trapping and local electric field fluctuations.…”

Section: Excitation and Relaxation Processes In Colloidal Nanocrystalsmentioning

confidence: 99%

Optical Properties of Spherical Colloidal Nanocrystals

Morello¹

2012

Fingerprints in the Optical and Transport Properties of Quantum Dots

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Recombination dynamics of luminescence in colloidal CdSe/ZnS quantum dots

Cited by 60 publications

References 25 publications

Controlled Synthesis of CdSe Quantum Dots by a Microwave‐Enhanced Process: A Green Approach for Mass Production

Controlled Synthesis of CdSe Quantum Dots by a Microwave‐Enhanced Process: A Green Approach for Mass Production

Quantitative modeling of the role of surface traps in CdSe/CdS/ZnS nanocrystal photoluminescence decay dynamics

Optical Properties of Spherical Colloidal Nanocrystals

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