Showing papers by "Moungi G. Bawendi published in 2015"
TL;DR: It is shown that many of these limitations can be overcome by replacing interferometric optics with a two-dimensional absorptive filter array composed of colloidal quantum dots, which will be useful in applications where minimizing size, weight, cost and complexity of the spectrometer are critical.
Abstract: Spectroscopy is carried out in almost every field of science, whenever light interacts with matter. Although sophisticated instruments with impressive performance characteristics are available, much effort continues to be invested in the development of miniaturized, cheap and easy-to-use systems. Current microspectrometer designs mostly use interference filters and interferometric optics that limit their photon efficiency, resolution and spectral range. Here we show that many of these limitations can be overcome by replacing interferometric optics with a two-dimensional absorptive filter array composed of colloidal quantum dots. Instead of measuring different bands of a spectrum individually after introducing temporal or spatial separations with gratings or interference-based narrowband filters, a colloidal quantum dot spectrometer measures a light spectrum based on the wavelength multiplexing principle: multiple spectral bands are encoded and detected simultaneously with one filter and one detector, respectively, with the array format allowing the process to be efficiently repeated many times using different filters with different encoding so that sufficient information is obtained to enable computational reconstruction of the target spectrum. We illustrate the performance of such a quantum dot microspectrometer, made from 195 different types of quantum dots with absorption features that cover a spectral range of 300 nanometres, by measuring shifts in spectral peak positions as small as one nanometre. Given this performance, demonstrable avenues for further improvement, the ease with which quantum dots can be processed and integrated, and their numerous finely tuneable bandgaps that cover a broad spectral range, we expect that quantum dot microspectrometers will be useful in applications where minimizing size, weight, cost and complexity of the spectrometer are critical.
410 citations
TL;DR: It is concluded that eliminating sub-bandgap states in PbS QD films has the potential to show a greater gain than may be attainable by optimization of interfaces between QDs and other materials.
Abstract: Quantum dot photovoltaics (QDPV) offer the potential for low-cost solar cells. To develop strategies for continued improvement in QDPVs, a better understanding of the factors that limit their performance is essential. Here, we study carrier recombination processes that limit the power conversion efficiency of PbS QDPVs. We demonstrate the presence of radiative sub-bandgap states and sub-bandgap state filling in operating devices by using photoluminescence (PL) and electroluminescence (EL) spectroscopy. These sub-bandgap states are most likely the origin of the high open-circuit-voltage (VOC) deficit and relatively limited carrier collection that have thus far been observed in QDPVs. Combining these results with our perspectives on recent progress in QDPV, we conclude that eliminating sub-bandgap states in PbS QD films has the potential to show a greater gain than may be attainable by optimization of interfaces between QDs and other materials. We suggest possible future directions that could guide the design of high-performance QDPVs.
221 citations
TL;DR: This work synthesizes phase-pure BiI3 thin films by physical vapor transport and solution processing and single-crystals by an electrodynamic gradient vertical Bridgman method and measures optical absorption and recombination lifetimes, which can also inform future selection of candidate PV absorbers.
Abstract: Guided by predictive discovery framework, we investigate bismuth triiodide (BiI3) as a candidate thin-film photovoltaic (PV) absorber. BiI3 was chosen for its optical properties and the potential for “defect-tolerant” charge transport properties, which we test experimentally by measuring optical absorption and recombination lifetimes. We synthesize phase-pure BiI3 thin films by physical vapor transport and solution processing and single-crystals by an electrodynamic gradient vertical Bridgman method. The bandgap of these materials is ∼1.8 eV, and they demonstrate room-temperature band-edge photoluminescence. We measure monoexponential recombination lifetimes in the range of 180–240 ps for thin films, and longer, multiexponential dynamics for single crystals, with time constants up to 1.3 to 1.5 ns. We discuss the outstanding challenges to developing BiI3 PVs, including mechanical and electrical properties, which can also inform future selection of candidate PV absorbers.
180 citations
TL;DR: Core-shell PbS-CdS quantum dots enhance the peak external quantum efficiency of shortwave-infrared light-emitting devices by up to 50-100-fold (compared with core-only PbBS devices).
Abstract: Core-shell PbS-CdS quantum dots enhance the peak external quantum efficiency of shortwave-infrared light-emitting devices by up to 50-100-fold (compared with core-only PbS devices). This is more than double the efficiency of previous quantum-dot light-emitting devices operating at wavelengths beyond 1 μm, and results from the passivation of the PbS cores by the CdS shells against in situ photoluminescence quenching.
165 citations
TL;DR: In this paper, a biocompatible quantum dot (QD)-Ab conjugates were developed by coupling whole mAbs to QDs coated with norbornene-displaying polyimidazole ligands using tetrazine-norbornene cycloaddition.
Abstract: Multiplexed, phenotypic, intravital cytometric imaging requires novel fluorophore conjugates that have an appropriate size for long circulation and diffusion and show virtually no nonspecific binding to cells/serum while binding to cells of interest with high specificity. In addition, these conjugates must be stable and maintain a high quantum yield in the in vivo environments. Here, we show that this can be achieved using compact (∼15 nm in hydrodynamic diameter) and biocompatible quantum dot (QD) -Ab conjugates. We developed these conjugates by coupling whole mAbs to QDs coated with norbornene-displaying polyimidazole ligands using tetrazine–norbornene cycloaddition. Our QD immunoconstructs were used for in vivo single-cell labeling in bone marrow. The intravital imaging studies using a chronic calvarial bone window showed that our QD-Ab conjugates diffuse into the entire bone marrow and efficiently label single cells belonging to rare populations of hematopoietic stem and progenitor cells (Sca1+c-Kit+ cells). This in vivo cytometric technique may be useful in a wide range of structural and functional imaging to study the interactions between cells and between a cell and its environment in intact and diseased tissues.
110 citations
TL;DR: The results establish the utility of the QD-micelle approach for in vivo biological sensing applications and provide a means for signal transduction under both one- and two-photon excitation.
Abstract: Micelles have been employed to encapsulate the supramolecular assembly of quantum dots with palladium(II) porphyrins for the quantification of O2 levels in aqueous media and in vivo. Forster resonance energy transfer from the quantum dot (QD) to the palladium porphyrin provides a means for signal transduction under both one- and two-photon excitation. The palladium porphyrins are sensitive to O2 concentrations in the range of 0–160 Torr. The micelle-encapsulated QD-porphyrin assemblies have been employed for in vivo multiphoton imaging and lifetime-based oxygen measurements in mice with chronic dorsal skinfold chambers or cranial windows. Our results establish the utility of the QD-micelle approach for in vivo biological sensing applications.
104 citations
TL;DR: Despite slowing down precursor conversion rate by multiple orders of magnitude, the less reactive precursors do not yield the expected increase in size and improvement in size distribution, disproves the widely accepted explanation for the shortcoming of current III-V QD syntheses and points to the need for a new generalizable theoretical picture for the mechanism of QD formation and growth.
Abstract: Control of quantum dot (QD) precursor chemistry has been expected to help improve the size control and uniformity of III-V QDs such as indium phosphide and indium arsenide. Indeed, experimental results for other QD systems are consistent with the theoretical prediction that the rate of precursor conversion is an important factor controlling QD size and size distribution. We synthesized and characterized the reactivity of a variety of group-V precursors in order to determine if precursor chemistry could be used to improve the quality of III-V QDs. Despite slowing down precursor conversion rate by multiple orders of magnitude, the less reactive precursors do not yield the expected increase in size and improvement in size distribution. This result disproves the widely accepted explanation for the shortcoming of current III-V QD syntheses and points to the need for a new generalizable theoretical picture for the mechanism of QD formation and growth.
75 citations
TL;DR: In this article, under-charged Pb atoms were oxidized to reduce the density of trap states by a factor of 40 in colloidal PbS quantum dots for devices.
Abstract: Chemical oxidation of under-charged Pb atoms reduces the density of trap states by a factor of 40 in films of colloidal PbS quantum dots for devices. These emissive sub-bandgap states are a byproduct of several standard ligand-exchange procedures. X-ray photoelectron spectro-scopy measurements and density function theory simulations demonstrate that they are associated with under-charged Pb.
73 citations
01 Jun 2015
TL;DR: In this paper, an ultra-bright, highly efficient, low roll-off, inverted quantum dot-based red light emitting device (QLED) using solution-processed zinc oxide nanoparticles and cesium carbonate films as the electron injection and hole blocking layers, respectively, has been obtained at a current density of 1000 mA/cm2 with a low driving voltage of 58 V.
Abstract: We report an ultra-bright, highly efficient, low roll-off, inverted quantum dot-based red light emitting device (QLED) using solution-processed zinc oxide nanoparticles and cesium carbonate films as the electron injection and hole blocking layers, respectively Record luminance of 165,000 Cd/m2 has been obtained at a current density of 1000 mA/cm2 with a low driving voltage of 58 V for deep red device with CIE coordinates of (069, 031)
72 citations
TL;DR: In this article, an automated two-phase small scale platform based on controlled oscillatory motion of a droplet within a 12 cm long tubular Teflon reactor is designed and developed for high-throughput in situ studies of a solution-phase preparation of semiconductor nanocrystals.
Abstract: An automated two-phase small scale platform based on controlled oscillatory motion of a droplet within a 12 cm long tubular Teflon reactor is designed and developed for high-throughput in situ studies of a solution-phase preparation of semiconductor nanocrystals. The unique oscillatory motion of the droplet within the heated region of the reactor enables temporal single-point spectral characterization of the same nanocrystals with a time resolution of 3 s over the course of the synthesis time without sampling while removing the residence time limitation associated with continuous flow-based strategies. The developed oscillatory microprocessor allows for direct comparison of the high temperature and room temperature spectral characteristics of nanocrystals. Utilizing this automated experimental strategy, we study the effect of temperature on the nucleation and growth of II–VI and III–V semiconductor nanocrystals. The automated droplet preparation and injection of the precursors combined with the oscillator...
69 citations
01 Nov 2015
TL;DR: A highly efficient thin-film luminescent solar concentrator utilizing two π-conjugated polymers as antennae for small amounts of the valued perylene bisimide Lumogen F Red 305 is presented.
Abstract: National Science Foundation (U.S.) (Graduate Research Fellowship Program (Grant No. 1122374))
TL;DR: In this paper, water impurities in indium myristate precursors can negatively impact indium phosphide nanoparticle growth by limiting its size tunability, and the inhibited growth behavior was attributed to the hydroxylation effect of water or free hydroxide.
Abstract: We report that trace amounts of water impurities in indium myristate precursors can negatively impact indium phosphide nanoparticle growth by limiting its size tunability. Without water, the growth can be effectively tuned by growth temperature and time with the first absorption peak reaching 620 nm; with water, the growth presents a “focused” behavior with the first absorption peak remaining around 550 nm. The results imply that water impurities, either from indium acetate derived indium precursors or generated in situ during nanoparticle growth, may be the cause of the currently observed inhibited growth behavior of indium phosphide quantum dots. We use multistage microfluidic reactors to show that this inhibiting effect occurs at the late stage of particle growth, following precursor depletion. We extend our study by showing that trace amounts of free hydroxide can also inhibit nanoparticle growth. We attribute the inhibited growth behavior to the hydroxylation effect of water or free hydroxide.
TL;DR: A reliable QD sizing curve is created using small-angle X-ray scattering, thin-film SAXS, a pair-distribution function for QD spacing, and a stacked-capacitor geometry to measure the capacitance of the thin film to support a reduced dielectric constant in nanoparticles.
Abstract: We study the dielectric constant of lead sulfide quantum dot (QD) films as a function of the volume fraction of QDs by varying the QD size and keeping the ligand constant. We create a reliable QD sizing curve using small-angle X-ray scattering (SAXS), thin-film SAXS to extract a pair-distribution function for QD spacing, and a stacked-capacitor geometry to measure the capacitance of the thin film. Our data support a reduced dielectric constant in nanoparticles.
TL;DR: Recovering the locations and lifetimes of fluorescent markers hidden behind a turbid layer is proposed and experimentally demonstrated, opening the door to various applications for non-invasive diagnosis, analysis, flowmetry and inspection.
Abstract: Fluorescent patches can be localized in 3D and identified behind a diffusive layer by use of streak images taken from one horizontal line on the diffusive barrier. Satat et al. show that the time-resolved inversion along with sparse prior can be used to perform this with deeper recovery range.
TL;DR: A 750-μm-thick Nd3+-doped YAG planar waveguide sensitized by a luminescent CdSe/CdZnS (core/shell) colloidal nanocrystal is reported, yielding a peak cascade energy transfer of 14%, a broad spectral response in the visible portion of the solar spectrum, and an equivalent quasi-CW solar lasing threshold of 23 W-cm−2.
Abstract: The optical conversion of incoherent solar radiation into a bright, coherent laser beam enables the application of nonlinear optics to solar energy conversion and storage. Here, we present an architecture for solar pumped lasers that uses a luminescent solar concentrator to decouple the conventional trade-off between solar absorption efficiency and the mode volume of the optical gain material. We report a 750-μm-thick Nd(3+)-doped YAG planar waveguide sensitized by a luminescent CdSe/CdZnS (core/shell) colloidal nanocrystal, yielding a peak cascade energy transfer of 14%, a broad spectral response in the visible portion of the solar spectrum, and an equivalent quasi-CW solar lasing threshold of 23 W-cm(-2), or approximately 230 suns. The efficient coupling of incoherent, spectrally broad sunlight in small gain volumes should allow the generation of coherent laser light from intensities of less than 100 suns.
TL;DR: The conduction mechanism changes from nearest neighbor hopping in oleic-acid-capped PbS dots to Mott's variable range hopping in n-butylamine capped Pbs dots, and the importance of the capping ligand on charge transport through colloidal quantum dot arrays is highlighted.
Abstract: Colloidal quantum dot arrays with long organic ligands have better packing order than those with short ligands but are highly resistive, making low-bias conductance measurements impossible with conventional two-probe techniques. We use an integrated charge sensor to study transport in weakly coupled arrays in the low-bias regime, and we nanopattern the arrays to minimize packing disorder. We present the temperature and field dependence of the resistance for nanopatterned oleic-acid and n-butylamine-capped PbS arrays, measuring resistances as high as 1018 Ω. We find that the conduction mechanism changes from nearest neighbor hopping in oleic-acid-capped PbS dots to Mott’s variable range hopping in n-butylamine capped PbS dots. Our results can be understood in terms of a change in the interdot coupling strength or a change in density of trap states and highlight the importance of the capping ligand on charge transport through colloidal quantum dot arrays.
TL;DR: It is found that two-photon scanning microscopy has approximately twice the penetration depth of temporal-focusing microscopy, and that penetration depth is organ-specific; the heart has the lowest penetration depth, followed by the liver, lungs, and kidneys, then the spleen, and finally white adipose tissue.
Abstract: Temporal focusing is a technique for performing axially resolved widefield multiphoton microscopy with a large field of view. Despite significant advantages over conventional point-scanning multiphoton microscopy in terms of imaging speed, the need to collect the whole image simultaneously means that it is expected to achieve a lower penetration depth in common biological samples compared to point-scanning. We assess the penetration depth using a rigorous objective criterion based on the modulation transfer function, comparing it to point-scanning multiphoton microscopy. Measurements are performed in a variety of mouse organs in order to provide practical guidance as to the achievable penetration depth for both imaging techniques. It is found that two-photon scanning microscopy has approximately twice the penetration depth of temporal-focusing microscopy, and that penetration depth is organ-specific; the heart has the lowest penetration depth, followed by the liver, lungs, and kidneys, then the spleen, and finally white adipose tissue.
Patent•
08 May 2015TL;DR: In this article, a method of improving performance of a photovoltaic device can include modifying a surface energy level of a nanocrystal through ligand exchange, which can improve the performance of the device.
Abstract: A method of improving performance of a photovoltaic device can include modifying a surface energy level of a nanocrystal through ligand exchange. A photovoltaic device can include a layer that includes a nanocrystal with a surface energy modified through ligand exchange.
TL;DR: Colloidal CdSe quantum dot core ensembles were photodimmed and allowed to recover in the dark using ambient thermal energy at a range of temperatures to intuitively describe the distributed kinetics observed and complements commonly proposed blinking mechanisms.
Abstract: Colloidal CdSe quantum dot (QD) core ensembles were photodimmed and allowed to recover in the dark using ambient thermal energy at a range of temperatures. Nonlinear thermal recovery is well described by a stretched exponential function, and further analysis yields an underlying probability distribution of rate constants. Casting the rate constants as a collection of first-order activated processes provides an activation barrier probability distribution with significant density at room-temperature thermal energy that peaks at 200 meV before decaying to zero. This treatment for the recovery transition intuitively describes the distributed kinetics observed and complements commonly proposed blinking mechanisms.
Patent•
10 Sep 2015TL;DR: A method of preparing a coated nanoparticle can include decomposing a compound to produce a nanoparticle, oxidizing the nanoparticle to produce an oxidized nanoparticle and coating the oxidised nanoparticle with a zwitterionic ligand to produce the coated nanoparticles as discussed by the authors.
Abstract: A method of preparing a coated nanoparticle can include decomposing a compound to produce a nanoparticle, oxidizing the nanoparticle to produce an oxidized nanoparticle, and coating the oxidized nanoparticle with a zwitterionic ligand to produce the coated nanoparticle. The coated nanoparticle or the nanoparticle can be used in magnetic resonance imaging.
Patent•
13 Nov 2015TL;DR: One method of preparing a nanoparticle can include decomposing a compound at a high temperature, adding an acid to the solvent to form a reaction mixture, increasing the temperature of the reaction mixture to boiling point of the mixture, and heating the mixture at the boiling point for 60 to 120 minutes to produce the nanoparticle as mentioned in this paper.
Abstract: One method of preparing a nanoparticle can include decomposing a compound at a high temperature, adding an acid to the solvent to form a reaction mixture, increasing the temperature of the reaction mixture to boiling point of the reaction mixture, and heating the reaction mixture at the boiling point for 60 to 120 minutes to produce the nanoparticle. The coated nanoparticle or the nanoparticle can be used in magnetic particles imaging.
10 May 2015
TL;DR: In this paper, bowtie apertures fabricated by lift-off were used to optically trap a 30-nm silica coated quantum dot (scQD) with 1.56-MW/cm2 intensity at 1064-nm wavelength.
Abstract: Bowtie apertures fabricated by lift-off were used to optically trap a 30-nm silica coated quantum dot (scQD) with 1.56-MW/cm2 intensity at 1064-nm wavelength. The trapped scQD emitted fluorescence by two photon excitation from the trapping laser.
01 Apr 2015
TL;DR: In this article, the authors assess the penetration depth using a rigorous objective criterion based on the modulation transfer function, comparing point-scanning multiphoton microscopy with temporal focusing.
Abstract: Temporal focusing is a technique for performing axially resolved widefield multiphoton microscopy with a large field of view. Despite significant advantages over conventional point-scanning multiphoton microscopy in terms of imaging speed, the need to collect the whole image simultaneously means that it is expected to achieve a lower penetration depth in common biological samples compared to point-scanning. We assess the penetration depth using a rigorous objective criterion based on the modulation transfer function, comparing it to point-scanning multiphoton microscopy. Measurements are performed in a variety of mouse organs in order to provide practical guidance as to the achievable penetration depth for both imaging techniques. It is found that two-photon scanning microscopy has approximately twice the penetration depth of temporal-focusing microscopy, and that penetration depth is organ-specific; the heart has the lowest penetration depth, followed by the liver, lungs, and kidneys, then the spleen, and finally white adipose tissue.
Patent•
10 Sep 2015
TL;DR: In this article, a procede de preparation d'une nanoparticule revetue is described, which consiste a decomposer un compose pour produire nano-particles, a oxyder la nanoparticle oxydee, and a enrober the nanoparticiule oxydie d'un ligand zwitterionique.
Abstract: L'invention concerne un procede de preparation d'une nanoparticule revetue qui consiste a decomposer un compose pour produire une nanoparticule, a oxyder la nanoparticule pour produire une nanoparticule oxydee, et a enrober la nanoparticule oxydee d'un ligand zwitterionique pour produire la nanoparticule enrobee La nanoparticule ou la nanoparticule enrobee peut etre utilisee dans l'imagerie par resonance magnetique