Influence of the core size on biexciton quantum yield of giant CdSe/CdS nanocrystals

Mangum, Benjamin D.; Sampat, Siddharth; Ghosh, Yagnaseni; Hollingsworth, Jennifer A.; Htoon, Han; Malko, Anton V.

doi:10.1039/c3nr06558h

Cited by 39 publications

(54 citation statements)

References 46 publications

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“…In sharp contrast, the biexciton emission QYs for QDs with a fixed core size but different shell thicknesses are almost constant (Supplementary Fig. 8), being consistent with the literature reports 29,41 . With and , the radiative and Auger non-radiative recombination rates of biexciton ( and ) can be calculated.…”

Section: Resultssupporting

confidence: 90%

Engineering Auger recombination in colloidal quantum dots via dielectric screening

et al. 2019

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Auger recombination is the main non-radiative decay pathway for multi-carrier states of colloidal quantum dots, which affects performance of most of their optical and optoelectronic applications. Outstanding single-exciton properties of CdSe/CdS core/shell quantum dots enable us to simultaneously study the two basic types of Auger recombination channels—negative trion and positive trion channels. Though Auger rates of positive trion are regarded to be much faster than that of negative trion for II-VI quantum dots in literature, our experiments find the two rates can be inverted for certain core/shell geometries. This is confirmed by theoretical calculations as a result of geometry-dependent dielectric screening. By varying the core/shell geometry, both types of Auger rates can be independently tuned for ~ 1 order of magnitude. Experimental and theoretical findings shed new light on designing quantum dots with necessary Auger recombination characteristics for high-power light-emitting-diodes, lasers, single-molecular tracking, super-resolution microscope, and advanced quantum light sources.

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Section: Resultssupporting

confidence: 90%

Engineering Auger recombination in colloidal quantum dots via dielectric screening

et al. 2019

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“…This enhancement is clearly evidenced by the histograms (Figure 2 d) showing the distribution of R. As a consequence of this enhancement, PL of the g-NQDs on graphene shows no saturation ( Figure 3 a) with an increase of pump fl uence as it has been commonly observed in PL of the g-NQDs on glass with Q 2X < 0.1. [ 23,24 ] This further indicates that this enhancement of R can lead to a real emission intensity enhancement at high pump fl uence.…”

Section: Communicationmentioning

confidence: 77%

Hybrid Graphene–Giant Nanocrystal Quantum Dot Assemblies with Highly Efficient Biexciton Emission

Gao

Roslyak

Dervishi

et al. 2014

Advanced Optical Materials

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COMMUNICATIONSXs and BXs with plasmons of metallic nanostructures. [ 12,13 ] This enhancement critically depends upon alignment between the energy of radiative transitions in a NQD and plasmonic resonance of a metal nanostructure, as well as an ability to couple NQDs to metal nanostructures at a distance where plasmonic enhancement of the radiative rates favors over the PL quenching via Förster energy transfer. In the case of the NQDgraphene coupled system, graphene's plasmonic resonances (lying in the IR and THz spectral regions, [14][15][16] make plasmonic enhancement of any of the NQDs' radiative transitions impossible. The semi-metallic band structure of graphene with its continuous distribution of the density of states also allows for very effi cient transfer of excitons from NQDs to graphene via a Förster process. It therefore appears and is confi rmed by a recent study [ 5 ] that the NQD-graphene coupling should only lead to strong quenching of the PL. However, the study was performed on standard NQDs, in which the PL emitting CdSe core is over-coated only by a thin ZnS (<2 ML, monolayer, thick) shell.Recently, giant nanocrystal quantum dots (g-NQDs), in which a CdSe core is over-coated with an ultra-thick single crystalline CdS shell, have been emerging as a new class of NQDs possessing such unique optical properties as nonblinking PL and strongly suppressed Auger recombination. [ 7,17,18 ] These g-NQDs possess structural, optical, and electronic properties that could alter the graphene-NQD interactions. Specifi cally, as the efficiency of Förster energy transfer is strongly dependent upon distance between donor (NQD core) and acceptor (graphene layer), the ultra-thick shells ( Figure 1 a) of these g-NQDs can provide necessary separation to suppress this process and signifi cantly reduce the PL quenching. The suppression of energy transfer by the thick shell has been observed in recent studies. [ 12,19 ] Furthermore, in contrast to standard NQDs, g-NQDs are characterized by quasi-type-II band alignment resulting in strong confi nement of the hole within the core and the electron delocalization to the shell. Our recent single-nanostructure electrochemistry study revealed that this asymmetric confi nement leads to near complete suppression of the Auger recombination of negatively charged exciton states and makes them highly emissive. [ 20 ] As photo-induced charging of the NQDs is known to occur on graphene effi ciently, [ 1 ] it becomes very interesting to see how the electric fi eld of charged g-NQDs could locally modify the electrochemical potential of graphene and how this modifi cation in turn affects the decay dynamics and emission effi ciencies of negatively charged SXs and BXs in the g-NQDs.To this end, we have performed single dot spectroscopy studies on g-NQDs overcoated with a 16 ML CdS shell spread Graphene sheets decorated with semiconducting, metallic, or magnetic nanocrystals are rapidly emerging as a new class of hybrid materials with many unique properties that are highly suited for a wide ...

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“…20 So far, the best result reported for the biexciton QY in colloidal NCs is 40%, averaged on all the studied QDs. 17,21 In the present study, we report a new generation of thick shell CdSe/CdS QDs that show, in air and at room temperature 100% QY for the biexciton for all the dots we observed. In addition, they present a completely suppressed blinking, no Auger recombination at least for the charged monoexciton and the biexciton, and a QY of 100% for the monoexciton as well as for the biexciton, strongly reduced Auger recombinations for higher-order multiexcitons and an emission color at the single-particle level that strongly depends on the excitation, yielding white-light emitting QDs at high excitation power.…”

mentioning

confidence: 81%

Gradient CdSe/CdS Quantum Dots with Room Temperature Biexciton Unity Quantum Yield

et al. 2015

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Auger recombination is a major limitation for the fluorescent emission of quantum dots (QDs). It is the main source of QDs fluorescence blinking at the single-particle level. At high-power excitation, when several charge carriers are formed inside a QD, Auger becomes more efficient and severely decreases the quantum yield (QY) of multiexcitons. This limits the efficiency and the use of colloidal QDs in applications where intense light output is required. Here, we present a new generation of thick-shell CdSe/CdS QDs with dimensions >40 nm and a composition gradient between the core and the shell that exhibits 100% QY for the emission of both the monoexciton and the biexciton in air and at room temperature for all the QDs we have observed. The fluorescence emission of these QDs is perfectly Poissonian at the single-particle level at different excitation levels and temperatures, from 30 to 300 K. In these QDs, the emission of high-order (>2) multiexcitons is quite efficient, and we observe white light emission at the single-QD level when high excitation power is used. These gradient thick shell QDs confirm the suppression of Auger recombination in gradient core/shell structures and help further establish the colloidal QDs with a gradient shell as a very stable source of light even under high excitation.

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Influence of the core size on biexciton quantum yield of giant CdSe/CdS nanocrystals

Cited by 39 publications

References 46 publications

Engineering Auger recombination in colloidal quantum dots via dielectric screening

Engineering Auger recombination in colloidal quantum dots via dielectric screening

Hybrid Graphene–Giant Nanocrystal Quantum Dot Assemblies with Highly Efficient Biexciton Emission

Gradient CdSe/CdS Quantum Dots with Room Temperature Biexciton Unity Quantum Yield

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