23 research outputs found

    Broadband Near-Infrared to Visible Upconversion in Quantum Dot–Quantum Well Heterostructures

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    Upconversion is a nonlinear process in which two, or more, long wavelength photons are converted to a shorter wavelength photon. It holds great promise for bioimaging, enabling spatially resolved imaging in a scattering specimen and for photovoltaic devices as a means to surpass the Shockley–Queisser efficiency limit. Here, we present dual near-infrared and visible emitting PbSe/CdSe/CdS nanocrystals able to upconvert a broad range of NIR wavelengths to visible emission at room temperature. The synthesis is a three-step process, which enables versatility and tunability of both the visible emission color and the NIR absorption edge. Using this method, one can achieve a range of desired upconverted emission peak positions with a suitable NIR band gap

    Super-resolved CARS by coherent image scanning

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    We present super-resolved coherent anti-Stokes Raman scattering (CARS) microscopy by implementing phase-resolved image scanning microscopy (ISM), achieving up to two-fold resolution increase as compared with a conventional CARS microscope. Phase-sensitivity is required for the standard pixel-reassignment procedure since the scattered field is coherent, thus the point-spread function (PSF) is well-defined only for the field amplitude. We resolve the complex field by a simple add-on to the CARS setup enabling inline interferometry. Phase-sensitivity offers additional contrast which informs the spatial distribution of both resonant and nonresonant scatterers. As compared with alternative super-resolution schemes in coherent nonlinear microscopy, the proposed method is simple, requires only low-intensity excitation, and is compatible with any conventional forward-detected CARS imaging setup

    Long-Lived Population Inversion in Isovalently Doped Quantum Dots

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    Optical gain from colloidal quantum dots has been desired for several decades since their discovery. While gain from multiexcitations is by now well-established, nonradiative Auger recombination limits the lifetime of such population inversion in quantum dots. CdSe cores isovalently doped by one to few Te atoms capped with rod-shaped CdS are examined as a candidate system for enhanced stimulated emission properties. Emission depletion spectroscopy shows a behavior characteristic of 3-level gain systems in these quantum dots. This implies complete removal of the 2-fold degeneracy of the lowest energy electronic excitation due to the large repulsive exciton–exciton interaction in the doubly excited state. Using emission depletion measurements of the trap-associated emission from poorly passivated CdS quantum dots, we show that 3-level characteristics are typical of emission resulting from a band edge to trap state transition, but reveal subtle differences between the two systems. These results allow for unprecedented observation of long-lived population inversion from singly excited quantum dots

    Quantum Dot Antennas for Photoelectrochemical Solar Cells

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    The use of Förster resonant energy transfer (FRET) has recently shown promise for significant improvement in various aspects of photoelectrochemical cells. Considering the particular case of semiconductor quantum dot donors, we show that they can enable broadening of the spectral response and increased optical density of the cell, thus increasing the current while potentially decreasing the electrode thickness. Moreover, the use of FRET and the separation of optical and electrical function within the cell provide flexibility in the choice of materials for both the antenna and sensitizer, opening new paths for performance optimization and achievement of long-term cell stability

    ExampleData2.zip

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    <div>Yonatan Israel, Ron Tenne, Dan Oron, and Yaron Silberberg,<br></div><div>Quantum correlation enhanced super-resolution localization using a fiber bundle camera</div><div>2017, Nature Communications</div><div><br></div><div>Description: ExampleData2 - Folder containing exmaple data used to generate Fig. 3 in the manuscript.</div

    Type-II Quantum-Dot-Sensitized Solar Cell Spanning the Visible and Near-Infrared Spectrum

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    Type-II heterostructure CdTe/CdSe core/shell nanocrystals (quantum dots, QDs) are explored as sensitizers in a QD-sensitized photoelectrochemical solar cell. These QDs comprise a hole-localizing core and an electron-localizing shell. Among their advantages is the significant red shift of the absorption edge of the heterostructured QD relative to its two constituents due to spatially indirect absorption leading to improved absorption characteristics, intraparticle exciton dissociation upon photoexcitation, and a relatively small content of the less abundant tellurium element. Upon incorporation in a sensitized solar cell utilizing a porous TiO<sub>2</sub> and a polysulfide electrolyte, these QDs exhibited efficient charge separation and high internal quantum efficiency despite hole localization in the CdTe core. Monochromatic incident photon-to-current conversion efficiency (IPCE) measurement shows a spectrally broad photoresponse spanning the whole visible spectrum and reaching up to ∼900 nm

    Enhanced Third-Harmonic Generation from a Metal/Semiconductor Core/Shell Hybrid Nanostructure

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    Nonlinear optical processes can be dramatically enhanced <i>via</i> the use of localized surface plasmon modes in metal nanoparticles. Here we show how more elaborate structures, based on shape-controlled Au/Cu<sub>2</sub>O core/shell nanostructures, enable further enhancement of the nanoparticle third-harmonic scattering cross-section. The semiconducting component takes a twofold role in this structure, both providing a knob to tune the resonant frequency of the gold plasmon and providing resonant enhancement by virtue of its excitonic states. The advantages and deficiencies of using such core/shell metal/semiconductor structures are discussed

    Nucleation, Growth, and Structural Transformations of Perovskite Nanocrystals

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    Despite the recent surge of interest in lead halide perovskite nanocrystals, there are still significant gaps in the understanding of nucleation and growth processes involved in their formation. Using CsPbX<sub>3</sub> as a model system, we systematically study the formation mechanism of cubic CsPbX<sub>3</sub> nanocrystals, their growth via oriented attachment into larger nanostructures, and the associated phase transformations. We found evidence to support that the formation of CsPbX<sub>3</sub> NCs occurs through the seed-mediated nucleation method, where Pb° NPs formed during the course of reaction act as seeds. Further growth occurs through self-assembly and oriented attachment. The polar environment is a major factor in determining the structure and shape of the resulting nanoparticles, as confirmed by experiments with aged seed reaction mixtures, and by addition of polar additives. These results provide a fundamental understanding of the influence of the environment polarity on self-assembly, self-healing, and the ability to control the morphology and structure over the perovskite structures. As a result of this understanding, we were able to extend the synthesis to produce other materials such as CsPbBr<sub>3</sub> nanowires and orthorhombic CsPbI<sub>3</sub> nanowires with tunable length ranging from 200 nm to several microns

    Study of Quantum Dot/Inorganic Layer/Dye Molecule Sandwich Structure for Electrochemical Solar Cells

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    A highly efficient quantum dot (QD)/inorganic layer/dye molecule sandwich structure was designed and applied in electrochemical QD-sensitized solar cells. The key component TiO<sub>2</sub>/CdS/ZnS/N719 hybrid photoanode with ZnS insertion between the two types of sensitizers was demonstrated not only to efficiently extend the light absorption but also to suppress the charge recombination from either TiO<sub>2</sub> or CdS QDs to electrolyte redox species, yielding a photocurrent density of 11.04 mA cm<sup>–2</sup>, an open-circuit voltage of 713 mV, a fill factor of 0.559, and an impressive overall energy conversion efficiency of 4.4%. More importantly, the cell exhibited enhanced photostability with the help of the synergistic stabilizing effect of both the organic and the inorganic passivation layers in the presence of a corrosive electrolyte
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