Co-reporter:Yue Chen, Daniel M. Montana, He Wei, Jose M. Cordero, Marc Schneider, Xavier Le Guével, Ou Chen, Oliver T. Bruns, and Moungi G. Bawendi
Nano Letters October 11, 2017 Volume 17(Issue 10) pp:6330-6330
Publication Date(Web):September 27, 2017
DOI:10.1021/acs.nanolett.7b03070
The use of visible/NIR-emitting gold nanoclusters (Au NCs), previously proposed for in vivo imaging, has been limited to some extent by low quantum yields (QYs) and the limited penetration of visible light in tissue. Here we report short wavelength infrared (SWIR, λ = 1–2 μm) emitting Au NCs with a good photoluminescence QY for this wavelength range (0.6% to 3.8% for λem = 1000 to 900 nm) and excellent stability under physiological conditions. We show that surface ligand chemistry is critical to achieving these properties. We demonstrate the potential of these SWIR-emitting Au NCs for in vivo imaging in mice. The Au NCs have a hydrodynamic diameter that is small (∼5 nm) enough that they exhibit a rapid renal clearance, and images taken in the SWIR region show better resolution of the blood vessels than in the NIR region.Keywords: Gold nanocluster; renal clearance; SWIR imaging; zwitterionic ligand;
Co-reporter:Hendrik Utzat, Katherine E. Shulenberger, Odin B. Achorn, Michel Nasilowski, Timothy S. Sinclair, and Moungi G. Bawendi
Nano Letters November 8, 2017 Volume 17(Issue 11) pp:6838-6838
Publication Date(Web):October 17, 2017
DOI:10.1021/acs.nanolett.7b03120
Cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals (PNCs) have recently become a promising material for optoelectronic applications due to their high emission quantum yields and facile band gap tunability via both halide composition and size. The spectroscopy of single PNCs enhances our understanding of the effect of confinement on excitations in PNCs in the absence of obfuscating ensemble averaging and can also inform synthetic efforts. However, single PNC studies have been hampered by poor PNC photostability under confocal excitation, precluding interrogation of all but the most stable PNCs, and leading to a lack of understanding of PNCs in the regime of high confinement. Here, we report the first comprehensive spectroscopic investigation of single PNC properties using solution-phase photon-correlation methods, including both highly confined and blue-emitting PNCs, previously inaccessible to single NC techniques. With minimally perturbative solution-phase photon-correlation Fourier spectroscopy (s-PCFS), we establish that the ensemble emission linewidth of PNCs of all sizes and compositions is predominantly determined by the intrinsic single PNC linewidth (homogeneous broadening). The single PNC linewidth, in turn, dramatically increases with increasing confinement, consistent with what has been found for II–VI semiconductor nanocrystals. With solution-phase photon antibunching measurements, we survey the biexciton-to-exciton quantum yield ratio (BX/X QY) in the absence of user-selection bias or photodegradation. Remarkably, the BX/X QY ratio depends both on the PNC size and halide composition, with values between ∼2% for highly confined bromide PNCs and ∼50% for intermediately confined iodide PNCs. Our results suggest a wide range of underlying Auger rates, likely due to transitory charge carrier separation in PNCs with relaxed confinement.Keywords: biexciton quantum yield; Cesium lead halide perovskites; perovskite nanocrystals; photon correlation Fourier spectroscopy; semiconductor nanocrystals; single nanocrystal spectroscopy; spectral lineshapes;
Co-reporter:Francesca S. Freyria, José M. Cordero, Justin R. Caram, Sandra Doria, Amro Dodin, Yue Chen, Adam P. Willard, and Moungi G. Bawendi
Nano Letters December 13, 2017 Volume 17(Issue 12) pp:7665-7665
Publication Date(Web):November 17, 2017
DOI:10.1021/acs.nanolett.7b03735
Enhancing photoluminescent emission (PL) in the near-infrared–infrared (NIR–IR) spectral region has broad applications from solar energy conversion to biological imaging. We show that self-assembled molecular dye J-aggregates (light-harvesting nanotubes, LHNs) can increase the PL emission of NIR PbS quantum dots (QDs) in both liquid and solid media more than 8-fold, promoted primarily by a long-range antenna effect and efficient Förster resonance energy transfer (FRET) from donor to acceptor. To create this composite material and preserve the optical properties of the nanocrystals, we performed an in situ ligand substitution followed by a functionalization reaction using click-chemistry. This resulted in PbS QDs soluble in an aqueous environment compatible with the molecular J-aggregates (LHNs). Theoretical and experimental results demonstrate that long-range diffusive exciton transport in LHNs enables efficient energy transfer to low concentrations of QDs despite there being no direct binding between molecular donors and QD acceptors. This suggests a broad application space for mixed light harvesting and photophysically active nanocomposite materials based on self-assembling molecular aggregates.Keywords: antenna effect; excitons; FRET; hybrid materials; J-aggregates; NIR PbS QDs; water-soluble QDs;
Co-reporter:Lea Nienhaus, Mengfei Wu, Nadav Geva, James J. Shepherd, Mark W. B. Wilson, Vladimir Bulović, Troy Van Voorhis, Marc A. Baldo, and Moungi G. Bawendi
ACS Nano August 22, 2017 Volume 11(Issue 8) pp:7848-7848
Publication Date(Web):July 26, 2017
DOI:10.1021/acsnano.7b02024
Hybrid interfaces combining inorganic and organic materials underpin the operation of many optoelectronic and photocatalytic systems and allow for innovative approaches to photon up- and down-conversion. However, the mechanism of exchange-mediated energy transfer of spin-triplet excitons across these interfaces remains obscure, particularly when both the macroscopic donor and acceptor are composed of many separately interacting nanoscopic moieties. Here, we study the transfer of excitons from colloidal lead sulfide (PbS) nanocrystals to the spin-triplet state of rubrene molecules. By reducing the length of the carboxylic acid ligands on the nanocrystal surface from 18 to 4 carbon atoms, thinning the effective ligand shell from 13 to 6 Å, we are able to increase the characteristic transfer rate by an order of magnitude. However, we observe that the energy transfer rate asymptotes for shorter separation distances (≤10 Å) which we attribute to the reduced Dexter coupling brought on by the increased effective dielectric constant of these solid-state devices when the aliphatic ligands are short. This implies that the shortest ligands, which hinder long-term colloidal stability, offer little advantage for energy transfer. Indeed, we find that hexanoic acid ligands are already sufficient for near-unity transfer efficiency. Using nanocrystals with these optimal-length ligands in an improved solid-state device structure, we obtain an upconversion efficiency of (7 ± 1)% with excitation at λ = 808 nm.Keywords: Dexter transfer; dielectric constant; triplet exciton transfer; triplet−triplet annihilation; upconversion;
Co-reporter:Yi Shen;Nopphon Weeranoppanant;Lisi Xie;Yue Chen;Marcella R. Lusardi;Joseph Imbrogno;Klavs F. Jensen
Nanoscale (2009-Present) 2017 vol. 9(Issue 23) pp:7703-7707
Publication Date(Web):2017/06/14
DOI:10.1039/C7NR01826F
This paper presents a fully-continuous novel liquid–liquid-extraction (LLE) platform for the purification of nanoparticles. The use of multistage operation enhances the purity of the final stream without the expense of high solvent consumption. Two case studies, purification of CdSe quantum dots in organic solvent and that of gold nanoparticles in water, demonstrate that the LLE platform is versatile, non-destructive, and highly efficient.
Co-reporter:Michel Nasilowski;Lea Nienhaus;Sophie N. Bertram
Chemical Communications 2017 vol. 53(Issue 32) pp:4517-4517
Publication Date(Web):2017/04/18
DOI:10.1039/C7CC90119D
Correction for ‘Colloidal atomic layer deposition growth of PbS/CdS core/shell quantum dots’ by Michel Nasilowski et al., Chem. Commun., 2017, 53, 869–872.
Co-reporter:Michel Nasilowski;Lea Nienhaus;Sophie N. Bertram
Chemical Communications 2017 vol. 53(Issue 5) pp:869-872
Publication Date(Web):2017/01/10
DOI:10.1039/C6CC07403K
Traditionally, PbS/CdS quantum dots (QDs) have been synthesized via a cation exchange method, making fine control over shell growth challenging. We show here that colloidal atomic layer deposition (c-ALD) allows for the sequential growth of single monolayers of the shell, thus creating a ‘true’ CdS shell on PbS QDs.
Co-reporter:Dr. Yi Shen; Dr. Milad Abolhasani;Yue Chen;Dr. Lisi Xie;Dr. Lu Yang;Connor W. Coley; Dr. Moungi G. Bawendi; Dr. Klavs F. Jensen
Angewandte Chemie 2017 Volume 129(Issue 51) pp:16551-16555
Publication Date(Web):2017/12/18
DOI:10.1002/ange.201710899
AbstractOscillatory flow reactors provide a surface energy-driven approach for automatically screening reaction conditions and studying reaction mechanisms of biphasic nanocrystal ligand-exchange reactions. Sulfide and cysteine ligand-exchange reactions with as-synthesized CdSe quantum dots (QDs) are chosen as two model reactions. Different reaction variables including the new-ligand-to-QD ratio, the size of the particles, and the original ligand type are examined systematically. Based on the in situ-obtained UV/Vis absorption spectra during the reaction, we propose two different exchange pathways for the sulfide exchange reaction.
Co-reporter:Dr. Yi Shen; Dr. Milad Abolhasani;Yue Chen;Dr. Lisi Xie;Dr. Lu Yang;Connor W. Coley; Dr. Moungi G. Bawendi; Dr. Klavs F. Jensen
Angewandte Chemie International Edition 2017 Volume 56(Issue 51) pp:16333-16337
Publication Date(Web):2017/12/18
DOI:10.1002/anie.201710899
AbstractOscillatory flow reactors provide a surface energy-driven approach for automatically screening reaction conditions and studying reaction mechanisms of biphasic nanocrystal ligand-exchange reactions. Sulfide and cysteine ligand-exchange reactions with as-synthesized CdSe quantum dots (QDs) are chosen as two model reactions. Different reaction variables including the new-ligand-to-QD ratio, the size of the particles, and the original ligand type are examined systematically. Based on the in situ-obtained UV/Vis absorption spectra during the reaction, we propose two different exchange pathways for the sulfide exchange reaction.
Co-reporter:Gregory D. Gutierrez;Igor Coropceanu;Timothy M. Swager
Advanced Materials 2016 Volume 28( Issue 3) pp:497-501
Publication Date(Web):
DOI:10.1002/adma.201504358
Co-reporter:Justin R. Caram, Sandra Doria, Dörthe M. Eisele, Francesca S. Freyria, Timothy S. Sinclair, Patrick Rebentrost, Seth Lloyd, and Moungi G. Bawendi
Nano Letters 2016 Volume 16(Issue 11) pp:6808-6815
Publication Date(Web):September 30, 2016
DOI:10.1021/acs.nanolett.6b02529
We report 1.6 ± 1 μm exciton transport in self-assembled supramolecular light-harvesting nanotubes (LHNs) assembled from amphiphillic cyanine dyes. We stabilize LHNs in a sucrose glass matrix, greatly reducing light and oxidative damage and allowing the observation of exciton–exciton annihilation signatures under weak excitation flux. Fitting to a one-dimensional diffusion model, we find an average exciton diffusion constant of 55 ± 20 cm2/s, among the highest measured for an organic system. We develop a simple model that uses cryogenic measurements of static and dynamic energetic disorder to estimate a diffusion constant of 32 cm2/s, in agreement with experiment. We ascribe large exciton diffusion lengths to low static and dynamic energetic disorder in LHNs. We argue that matrix-stabilized LHNS represent an excellent model system to study coherent excitonic transport.Keywords: coherent exciton; exciton; exciton delocalization; exciton diffusion; J-aggregate; molecular aggregate;
Co-reporter:Justin R. Caram, Sophie N. Bertram, Hendrik Utzat, Whitney R. Hess, Jessica A. Carr, Thomas S. Bischof, Andrew P. Beyler, Mark W. B. Wilson, and Moungi G. Bawendi
Nano Letters 2016 Volume 16(Issue 10) pp:6070-6077
Publication Date(Web):September 14, 2016
DOI:10.1021/acs.nanolett.6b02147
Lead chalcogenide colloidal nanocrystals (NCs) are promising materials for solution processable optoelectronics. However, there is little agreement on the identity and character of PbS NC emission for different degrees of quantum confinement—a critical parameter for realizing applications for these nanocrystals. In this work, we combine ensemble and single NC spectroscopies to interrogate preparations of lead sulfide NCs. We use solution photon correlation Fourier spectroscopy (S-PCFS) to measure the average single NC linewidth of near-infrared-emitting PbS quantum dots and find it to be dominated by homogeneous broadening. We further characterize PbS NCs using temperature-dependent linear and time-resolved emission spectroscopy which demonstrate that a kinetically accessed defect state dominates room temperature emission of highly confined emitting NCs. These experiments, taken together, demonstrate that the linewidth and Stokes shift of PbS NCs are the result of emission from two states: a thermally accessed defect—with an energetically pinned charge carrier—and an inhomogeneously broadened band-edge state.Keywords: Colloidal quantum dots; nanoparticle synthesis; near infrared emission; PbS nanocrystals; photon correlation Fourier spectroscopy; semiconductor nanocrystals; spectral linewidth;
Co-reporter:Jian Cui, Andrew P. Beyler, Igor Coropceanu, Liam Cleary, Thomas R. Avila, Yue Chen, José M. Cordero, S. Leigh Heathcote, Daniel K. Harris, Ou Chen, Jianshu Cao, and Moungi G. Bawendi
Nano Letters 2016 Volume 16(Issue 1) pp:289-296
Publication Date(Web):December 4, 2015
DOI:10.1021/acs.nanolett.5b03790
The optimization of photoluminescence spectral linewidths in semiconductor nanocrystal preparations involves minimizing both the homogeneous and inhomogeneous contributions to the ensemble spectrum. Although the inhomogeneous contribution can be controlled by eliminating interparticle inhomogeneities, far less is known about how to synthetically control the homogeneous, or single-nanocrystal, spectral linewidth. Here, we use solution photon-correlation Fourier spectroscopy (S-PCFS) to measure how the sample-averaged single-nanocrystal emission linewidth of CdSe core and core/shell nanocrystals change with systematic changes in the size of the cores and the thickness and composition of the shells. We find that the single-nanocrystal linewidth at room temperature is heavily influenced by the nature of the CdSe surface and the epitaxial shell, which have a profound impact on the internal electric fields that affect exciton–phonon coupling. Our results explain the wide variations, both experimental and theoretical, in the magnitude and size dependence in previous reports on exciton–phonon coupling in CdSe nanocrystals. Moreover, our findings offer a general pathway for achieving the narrow spectral linewidths required for many applications of nanocrystals.
Co-reporter:Lisi Xie, Yi Shen, Daniel Franke, Víctor Sebastián, Moungi G. Bawendi, and Klavs F. Jensen
Journal of the American Chemical Society 2016 Volume 138(Issue 41) pp:13469-13472
Publication Date(Web):October 3, 2016
DOI:10.1021/jacs.6b06468
Clusters have been identified as important growth intermediates during group III–V quantum dot (QD) formation. Here we report a one-solvent protocol that integrates synthesis, purification, and mass characterization of indium phosphide (InP) QD growth mixtures. The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) successfully tracks the evolution of clusters and the formation of QDs throughout the synthesis. Similar clusters are observed during the formation of large particles, suggesting that these clusters serve as a reservoir for QD formation. Combining MALDI and NMR techniques further enables us to extract extinction coefficients and construct sizing curves for cluster-free InP QDs. The use of MALDI MS opens new opportunities for characterization and mechanistic studies of small-sized air-sensitive clusters or QDs.
Co-reporter:Igor Coropceanu, Aurelio Rossinelli, Justin R. Caram, Francesca S. Freyria, and Moungi G. Bawendi
ACS Nano 2016 Volume 10(Issue 3) pp:3295
Publication Date(Web):February 17, 2016
DOI:10.1021/acsnano.5b06772
A two-step process has been developed for growing the shell of CdSe/CdS core/shell nanorods. The method combines an established fast-injection-based step to create the initial elongated shell with a second slow-injection growth that allows for a systematic variation of the shell thickness while maintaining a high degree of monodispersity at the batch level and enhancing the uniformity at the single-nanorod level. The second growth step resulted in nanorods exhibiting a fluorescence quantum yield up to 100% as well as effectively complete energy transfer from the shell to the core. This improvement suggests that the second step is associated with a strong suppression of the nonradiative channels operating both before and after the thermalization of the exciton. This hypothesis is supported by the suppression of a defect band, ubiquitous to CdSe-based nanocrystals after the second growth.Keywords: CdSe/CdS; nanorod; optical downshifting
Co-reporter:Dong-Kyun Ko, Andrea Maurano, Su Kyung Suh, Donghun Kim, Gyu Weon Hwang, Jeffrey C. Grossman, Vladimir Bulović, and Moungi G. Bawendi
ACS Nano 2016 Volume 10(Issue 3) pp:3382
Publication Date(Web):February 24, 2016
DOI:10.1021/acsnano.5b07186
Recent advances in quantum dot surface passivation have led to a rapid development of high-efficiency solar cells. Another critical element for achieving efficient power conversion is the charge neutrality of quantum dots, as charge imbalances induce electronic states inside the energy gap. Here we investigate how the simultaneous introduction of metal cations and halide anions modifies the charge balance and enhances the solar cell efficiency. The addition of metal salts between QD deposition and ligand exchange with 1,3-BDT results in an increase in the short-circuit current and fill factor, accompanied by a distinct reduction in a crossover between light and dark current density–voltage characteristics.Keywords: metal salts; nanocrystals; photovoltaics; quantum dots; solar cells
Co-reporter:Russell A. Jensen, I-Chun Huang, Ou Chen, Jennifer T. Choy, Thomas S. Bischof, Marko Lončar, and Moungi G. Bawendi
ACS Photonics 2016 Volume 3(Issue 3) pp:
Publication Date(Web):January 25, 2016
DOI:10.1021/acsphotonics.5b00575
We demonstrate bowtie apertures that were designed and fabricated by a lift-off process to optically trap individual, 30 nm, silica-coated quantum dots (scQD). Simulations and experiments confirm the trapping capability of the system with a relatively low continuous wave trapping flux of 1.56 MW/cm2 at 1064 nm. Additionally, the scQD emits upon trapping via two-photon excitation from the trapping laser due to strong field enhancement inside the aperture. This system is an exciting platform for studying light–matter interactions and mulitphoton processes in single emitters.
Co-reporter:Jessica A. Carr;Tulio A. Valdez;Oliver T. Bruns
PNAS 2016 Volume 113 (Issue 36 ) pp:9989-9994
Publication Date(Web):2016-09-06
DOI:10.1073/pnas.1610529113
Visualizing structures deep inside opaque biological tissues is one of the central challenges in biomedical imaging. Optical
imaging with visible light provides high resolution and sensitivity; however, scattering and absorption of light by tissue
limits the imaging depth to superficial features. Imaging with shortwave infrared light (SWIR, 1–2 μm) shares many advantages
of visible imaging, but light scattering in tissue is reduced, providing sufficient optical penetration depth to noninvasively
interrogate subsurface tissue features. However, the clinical potential of this approach has been largely unexplored because
suitable detectors, until recently, have been either unavailable or cost prohibitive. Here, taking advantage of newly available
detector technology, we demonstrate the potential of SWIR light to improve diagnostics through the development of a medical
otoscope for determining middle ear pathologies. We show that SWIR otoscopy has the potential to provide valuable diagnostic
information complementary to that provided by visible pneumotoscopy. We show that in healthy adult human ears, deeper tissue
penetration of SWIR light allows better visualization of middle ear structures through the tympanic membrane, including the
ossicular chain, promontory, round window niche, and chorda tympani. In addition, we investigate the potential for detection
of middle ear fluid, which has significant implications for diagnosing otitis media, the overdiagnosis of which is a primary
factor in increased antibiotic resistance. Middle ear fluid shows strong light absorption between 1,400 and 1,550 nm, enabling
straightforward fluid detection in a model using the SWIR otoscope. Moreover, our device is easily translatable to the clinic,
as the ergonomics, visual output, and operation are similar to a conventional otoscope.
Co-reporter:Gyu Weon Hwang;Donghun Kim;Jose M. Cordero;Mark W. B. Wilson;Chia-Hao M. Chuang;Jeffrey C. Grossman
Advanced Materials 2015 Volume 27( Issue 30) pp:4481-4486
Publication Date(Web):
DOI:10.1002/adma.201501156
Co-reporter:Darcy D. W. Grinolds, Patrick R. Brown, Daniel K. Harris, Vladimir Bulovic, and Moungi G. Bawendi
Nano Letters 2015 Volume 15(Issue 1) pp:21-26
Publication Date(Web):December 22, 2014
DOI:10.1021/nl5024244
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.
Co-reporter:Chia-Hao Marcus Chuang, Andrea Maurano, Riley E. Brandt, Gyu Weon Hwang, Joel Jean, Tonio Buonassisi, Vladimir Bulović, and Moungi G. Bawendi
Nano Letters 2015 Volume 15(Issue 5) pp:3286-3294
Publication Date(Web):April 30, 2015
DOI:10.1021/acs.nanolett.5b00513
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.
Co-reporter:Christopher M. Lemon; Elizabeth Karnas; Xiaoxing Han; Oliver T. Bruns; Thomas J. Kempa; Dai Fukumura; Moungi G. Bawendi; Rakesh K. Jain; Dan G. Duda;Daniel G. Nocera
Journal of the American Chemical Society 2015 Volume 137(Issue 31) pp:9832-9842
Publication Date(Web):July 7, 2015
DOI:10.1021/jacs.5b04765
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. Förster 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.
Co-reporter:Lisi Xie, Daniel K. Harris, Moungi G. Bawendi, and Klavs F. Jensen
Chemistry of Materials 2015 Volume 27(Issue 14) pp:5058
Publication Date(Web):July 7, 2015
DOI:10.1021/acs.chemmater.5b01626
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.
Co-reporter:Milad Abolhasani, Connor W. Coley, Lisi Xie, Ou Chen, Moungi G. Bawendi, and Klavs F. Jensen
Chemistry of Materials 2015 Volume 27(Issue 17) pp:6131
Publication Date(Web):August 13, 2015
DOI:10.1021/acs.chemmater.5b02821
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 oscillatory flow technique allows 7500 spectral data within a parameter space of 10 min reaction time at ten different temperatures and five different precursor ratios to be obtained automatically using only 250 μL of each precursor solution. The oscillatory microprocessor platform provides real-time in situ spectral information at the synthesis temperature, vital for fundamental studies of different mechanisms involved during the nucleation and growth stages of different types of nanomaterials.
Co-reporter:Hee-Sun Han;Elisabeth Niemeyer;Yuhui Huang;Walid S. Kamoun;John D. Martin;Jayeeta Bhaumik;Yunching Chen;Sylvie Roberge;Jian Cui;Margaret R. Martin;Dai Fukumura;Rakesh K. Jain;Dan G. Duda;
Proceedings of the National Academy of Sciences 2015 112(5) pp:1350-1355
Publication Date(Web):January 20, 2015
DOI:10.1073/pnas.1421632111
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.
Co-reporter:Russell A. Jensen; Igor Coropceanu; Yue Chen
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 15) pp:2933-2937
Publication Date(Web):July 14, 2015
DOI:10.1021/acs.jpclett.5b00989
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.
Co-reporter:Daniel Franke;Dr. Daniel K. Harris;Lisi Xie; Klavs F. Jensen; Moungi G. Bawendi
Angewandte Chemie International Edition 2015 Volume 54( Issue 48) pp:14299-14303
Publication Date(Web):
DOI:10.1002/anie.201505972
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.
Co-reporter:Daniel Franke;Dr. Daniel K. Harris;Lisi Xie; Klavs F. Jensen; Moungi G. Bawendi
Angewandte Chemie 2015 Volume 127( Issue 48) pp:14507-14511
Publication Date(Web):
DOI:10.1002/ange.201505972
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.
Co-reporter:Jian Cui, Andrew P. Beyler, Thomas S. Bischof, Mark W. B. Wilson and Moungi G. Bawendi
Chemical Society Reviews 2014 vol. 43(Issue 4) pp:1287-1310
Publication Date(Web):27 Nov 2013
DOI:10.1039/C3CS60330J
Prior to the advent of single-molecule fluorescence spectroscopy, many of the fundamental optical properties of colloidal semiconductor nanocrystal quantum dots were obscured by ensemble averaging over their inherent inhomogeneities. Single quantum dot spectroscopy has become a leading technique for the unambiguous determination of the governing excitonic physics of these quantum-confined systems. The analysis and interpretation of the timing and energies of photons emitted from individual nanocrystals have uncovered unexpected and fundamental electronic processes at the nanoscale. We review several different paradigms for deconstructing the photon stream from single nanocrystals, ranging from intensity “binning” techniques to more sophisticated methods based on single-photon counting. In particular, we highlight photon correlation – a powerful developing paradigm in single-nanocrystal studies. The application of photon-correlation techniques to single nanocrystals is changing the study of multiexcitonic recombination dynamics, uncovering the basic processes governing spectral linewidths and spectral diffusion, and enabling the extraction of single-nanocrystal properties directly from an ensemble with high statistical significance. These single-molecule techniques have proven invaluable for understanding the physics of nanocrystals and can provide unique insight into other heterogeneous and dynamical systems.
Co-reporter:Dong-Kyun Ko;Patrick R. Brown;Vladimir Bulovi&x107;
Advanced Materials 2014 Volume 26( Issue 28) pp:4845-4850
Publication Date(Web):
DOI:10.1002/adma.201401250
Co-reporter:Andrew P. Beyler, Thomas S. Bischof, Jian Cui, Igor Coropceanu, Daniel K. Harris, and Moungi G. Bawendi
Nano Letters 2014 Volume 14(Issue 12) pp:6792-6798
Publication Date(Web):November 19, 2014
DOI:10.1021/nl5027953
The brightness of nanoscale optical materials such as semiconductor nanocrystals is currently limited in high excitation flux applications by inefficient multiexciton fluorescence. We have devised a solution-phase photon correlation measurement that can conveniently and reliably measure the average biexciton-to-exciton quantum yield ratio of an entire sample without user selection bias. This technique can be used to investigate the multiexciton recombination dynamics of a broad scope of synthetically underdeveloped materials, including those with low exciton quantum yields and poor fluorescence stability. Here, we have applied this method to measure weak biexciton fluorescence in samples of visible-emitting InP/ZnS and InAs/ZnS core/shell nanocrystals, and to demonstrate that a rapid CdS shell growth procedure can markedly increase the biexciton fluorescence of CdSe nanocrystals.
Co-reporter:Thomas S. Bischof, Raoul E. Correa, Danna Rosenberg, Eric A. Dauler, and Moungi G. Bawendi
Nano Letters 2014 Volume 14(Issue 12) pp:6787-6791
Publication Date(Web):November 17, 2014
DOI:10.1021/nl502180w
The understanding of the photophysics of visible-emitting colloidal nanocrystals (NCs) has long been aided by single-molecule studies of their emission. Until recently, no suitable detection technologies have existed for corresponding studies of shortwave-infrared (SWIR) emitters. Now, the use of superconducting nanowire single-photon detectors (SNSPDs) enables the detailed study of SWIR NC emission dynamics at the single-emitter level. Here, we report a detailed analysis of the emission dynamics of individual InAs/CdZnS NCs emitting in the SWIR region. We observe blinking akin to the type A and type B blinking previously observed in visible-emitting CdSe NCs. We determine the intrinsic radiative lifetime of several InAs/CdZnS NCs and find examples ranging from 50–200 ns, indicative of a quasi-type-II electronic structure. We also measure g0(2) for several of these NCs and find that their biexciton emission quantum yields vary from <1% up to 43%.
Co-reporter:Igor Coropceanu and Moungi G. Bawendi
Nano Letters 2014 Volume 14(Issue 7) pp:4097-4101
Publication Date(Web):June 6, 2014
DOI:10.1021/nl501627e
CdSe/CdS core/shell quantum dots (QDs) have been optimized toward luminescent solar concentration (LSC) applications. Systematically increasing the shell thickness continuously reduced reabsorption up to a factor of 45 for the thickest QDs studied (with ca. 14 monolayers of CdS) compared to the initial CdSe cores. Moreover, an improved synthetic method was developed that retains a high-fluorescence quantum yield, even for particles with the thickest shell volume, for which a quantum yield of 86% was measured in solution. These high quantum yield thick shell quantum dots were embedded in a polymer matrix, yielding highly transparent composites to serve as prototype LSCs, which exhibited an optical efficiency as high as 48%. A Monte Carlo simulation was developed to model LSC performance and to identify the major loss channels for LSCs incorporating the materials developed. The results of the simulation are in excellent agreement with the experimental data.
Co-reporter:Camilla Lelii, Moungi G. Bawendi, Paolo Biagini, Po-Yen Chen, Marcello Crucianelli, Julio M. D'Arcy, Francesco De Angelis, Paula T. Hammond and Riccardo Po
Journal of Materials Chemistry A 2014 vol. 2(Issue 43) pp:18375-18382
Publication Date(Web):29 Aug 2014
DOI:10.1039/C4TA03098B
CdSe quantum dots of two different sizes exhibiting a maximum emission at 495 nm (CdSe495) and 545 nm (CdSe545) were combined with di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4-dicarboxylato)ruthenium(II) (N719) or 2-cyano-3-{5-[7-(4-diphenylamino-phenyl)benzo[1,2,5]thiadiazol-4-yl]-thiophen-2-yl}-acrylic acid (TBTCA) resulting in four novel hybrid organic–inorganic sensitizers, which were used in the fabrication of dye-sensitized solar cells. The results showed that with N719, both the CdSe dots decreased the power conversion efficiencies when compared to a standard device consisting only of N719 as the sensitizer. With the organic dye TBTCA, CdSe545 showed no significant effect, while CdSe495 interacted favorably, leading to a 25% increase in power conversion efficiency compared to a device sensitized solely by TBTCA. Studies on excited-state lifetimes of N719 in the presence of CdSe did not distinguish between energy and/or charge transfer mechanisms. On the other hand, time correlated single photon counting experiments on the photoelectrodes suggest that the advantages due to the CdSe495–TBTCA combination could be ascribed to FRET from quantum dots to the organic dye and to a further contribution, as suggested by IPCE spectra, consisting of electron transfer via cascade from the LUMO level of TBTCA to CdSe495 to TiO2, which produces a higher flux of electrons in the external circuit.
Co-reporter:Dörthe M. Eisele;Dylan H. Arias;Xiaofeng Fu;Erik A. Bloemsma;Colby P. Steiner;Russell A. Jensen;Holger Eisele;Patrick Rebentrost;Andrei Tokmakoff;Seth Lloyd;Keith A. Nelson;Daniela Nicastro;Jasper Knoester
PNAS 2014 Volume 111 (Issue 33 ) pp:E3367-E3375
Publication Date(Web):2014-08-19
DOI:10.1073/pnas.1408342111
Nature's highly efficient light-harvesting antennae, such as those found in green sulfur bacteria, consist of supramolecular
building blocks that self-assemble into a hierarchy of close-packed structures. In an effort to mimic the fundamental processes
that govern nature’s efficient systems, it is important to elucidate the role of each level of hierarchy: from molecule, to
supramolecular building block, to close-packed building blocks. Here, we study the impact of hierarchical structure. We present
a model system that mirrors nature’s complexity: cylinders self-assembled from cyanine-dye molecules. Our work reveals that
even though close-packing may alter the cylinders’ soft mesoscopic structure, robust delocalized excitons are retained: Internal
order and strong excitation-transfer interactions—prerequisites for efficient energy transport—are both maintained. Our results
suggest that the cylindrical geometry strongly favors robust excitons; it presents a rational design that is potentially key
to nature’s high efficiency, allowing construction of efficient light-harvesting devices even from soft, supramolecular materials.
Co-reporter:Darcy D. Wanger, Raoul E. Correa, Eric A. Dauler, and Moungi G. Bawendi
Nano Letters 2013 Volume 13(Issue 12) pp:5907-5912
Publication Date(Web):November 20, 2013
DOI:10.1021/nl402886j
We present a quantitative measurement of the number of trapped carriers combined with a measurement of exciton quenching to assess limiting mechanisms for current losses in PbS-quantum-dot-based photovoltaic devices. We use photocurrent intensity dependence and short-wave infrared transient photoluminescence and correlate these with device performance. We find that the effective density of trapped carriers ranges from 1 in 10 to 1 in 10 000 quantum dots, depending on ligand treatment, and that nonradiative exciton quenching, as opposed to recombination with trapped carriers, is likely the limiting mechanism in these devices.
Co-reporter:Liang-Yi Chang, Richard R. Lunt, Patrick R. Brown, Vladimir Bulović, and Moungi G. Bawendi
Nano Letters 2013 Volume 13(Issue 3) pp:994-999
Publication Date(Web):February 13, 2013
DOI:10.1021/nl3041417
PbS colloidal quantum dot heterojunction solar cells have shown significant improvements in performance, mostly based on devices that use high-temperature annealed transition metal oxides to create rectifying junctions with quantum dot thin films. Here, we demonstrate a solar cell based on the heterojunction formed between PbS colloidal quantum dot layers and CdS thin films that are deposited via a solution process at 80 °C. The resultant device, employing a 1,2-ethanedithiol ligand exchange scheme, exhibits an average power conversion efficiency of 3.5%. Through a combination of thickness-dependent current density–voltage characteristics, optical modeling, and capacitance measurements, the combined diffusion length and depletion width in the PbS quantum dot layer is found to be approximately 170 nm.
Co-reporter:Christopher M. Lemon, Elizabeth Karnas, Moungi G. Bawendi, and Daniel G. Nocera
Inorganic Chemistry 2013 Volume 52(Issue 18) pp:10394-10406
Publication Date(Web):August 26, 2013
DOI:10.1021/ic4011168
Supramolecular assemblies of a quantum dot (QD) associated to palladium(II) porphyrins have been developed to detect oxygen (pO2) in organic solvents. Palladium porphyrins are sensitive in the 0–160 Torr range, making them ideal phosphors for in vivo biological oxygen quantification. Porphyrins with meso pyridyl substituents bind to the surface of the QD to produce self-assembled nanosensors. Appreciable overlap between QD emission and porphyrin absorption features results in efficient Förster resonance energy transfer (FRET) for signal transduction in these sensors. The QD serves as a photon antenna, enhancing porphyrin emission under both one- and two-photon excitation, demonstrating that QD-palladium porphyrin conjugates may be used for oxygen sensing over physiological oxygen ranges.
Co-reporter:He Wei, Oliver T. Bruns, Ou Chen and Moungi G. Bawendi
Integrative Biology 2013 vol. 5(Issue 1) pp:108-114
Publication Date(Web):05 Oct 2012
DOI:10.1039/C2IB20142A
We have recently developed compact and water-soluble zwitterionic dopamine sulfonate (ZDS) ligand coated superparamagnetic iron oxide nanoparticles (SPIONs) for use in various biomedical applications. The defining characteristics of ZDS-coated SPIONs are small hydrodynamic diameters, low non-specific interactions with fetal bovine serum, the opportunity for specific labeling, and stability with respect to time, pH, and salinity. We report here on the magnetic characterization of ZDS-coated SPIONs and their in vitro and in vivo performance relative to non-specific interactions with HeLa cells and in mice, respectively. ZDS-coated SPIONs retained the superparamagnetism and saturation magnetization (Ms) of as-synthesized hydrophobic SPIONs, with Ms = 74 emu g−1 [Fe]. Moreover, ZDS-coated SPIONs showed only small non-specific uptake into HeLa cancer cells in vitro and low non-specific binding to serum proteins in vivo in mice.
Co-reporter:Dr. Euan R. Kay;Jungmin Lee; Daniel G. Nocera; Moungi G. Bawendi
Angewandte Chemie 2013 Volume 125( Issue 4) pp:1203-1207
Publication Date(Web):
DOI:10.1002/ange.201207181
Co-reporter:Dr. Hee-Sun Han;John D. Martin;Jungmin Lee;Daniel K. Harris;Dr. Dai Fukumura;Dr. Rakesh K. Jain;Dr. Moungi Bawendi
Angewandte Chemie 2013 Volume 125( Issue 5) pp:1454-1459
Publication Date(Web):
DOI:10.1002/ange.201208331
Co-reporter:Dr. Euan R. Kay;Jungmin Lee; Daniel G. Nocera; Moungi G. Bawendi
Angewandte Chemie International Edition 2013 Volume 52( Issue 4) pp:1165-1169
Publication Date(Web):
DOI:10.1002/anie.201207181
Co-reporter:Dr. Hee-Sun Han;John D. Martin;Jungmin Lee;Daniel K. Harris;Dr. Dai Fukumura;Dr. Rakesh K. Jain;Dr. Moungi Bawendi
Angewandte Chemie International Edition 2013 Volume 52( Issue 5) pp:1414-1419
Publication Date(Web):
DOI:10.1002/anie.201208331
Co-reporter:David B. Strasfeld, August Dorn, Darcy D. Wanger, and Moungi G. Bawendi
Nano Letters 2012 Volume 12(Issue 2) pp:569-575
Publication Date(Web):January 17, 2012
DOI:10.1021/nl204116b
We fabricated planar PbS quantum dot devices with ohmic and Schottky type electrodes and characterized them using scanning photocurrent and photovoltage microscopies. The microscopy techniques used in this investigation allow for interrogation of the lateral depletion width and related photovoltaic properties in the planar Schottky type contacts. Titanium/QD contacts exhibited depletion widths that varied over a wide range as a function of bias voltage, while the gold/QD contacts showed ohmic behavior over the same voltage range.
Co-reporter:Raoul E. Correa, Eric A. Dauler, Gautham Nair, Si H. Pan, Danna Rosenberg, Andrew J. Kerman, Richard J. Molnar, Xiaolong Hu, Francesco Marsili, Vikas Anant, Karl K. Berggren, and Moungi G. Bawendi
Nano Letters 2012 Volume 12(Issue 6) pp:2953-2958
Publication Date(Web):May 24, 2012
DOI:10.1021/nl300642k
Experimental restrictions imposed on the collection and detection of shortwave-infrared photons (SWIR) have impeded single molecule work on a large class of materials whose optical activity lies in the SWIR. Here we report the successful observation of room-temperature single nanocrystal photoluminescence at SWIR wavelengths using a highly efficient multielement superconducting nanowire single photon detector. We confirm that the photoluminescence from single lead sulfide nanocrystals is strongly antibunched, demonstrating the feasibility of performing sophisticated photon correlation experiments on individual weak SWIR emitters, and, more broadly, paving the way for sensitive measurements of spectral observables on infrared quantum systems that are incompatible with current detection techniques.
Co-reporter:Jing Zhao, Ou Chen, David B. Strasfeld, and Moungi G. Bawendi
Nano Letters 2012 Volume 12(Issue 9) pp:4477-4483
Publication Date(Web):August 7, 2012
DOI:10.1021/nl3013727
We explore biexciton (BX) nonradiative recombination processes in single semiconductor nanocrystals (NCs) using confocal fluorescence microscopy and second-order photon intensity correlation. More specifically, we measure the photoluminescence blinking and BX quantum yields (QYs) and study the correlation between these two measurements for single core (shell) CdSe (CdS) nanocrystals (NCs). We find that NCs with a high “on” time fraction are significantly more likely to have a high BX QY than NCs with a low “on” fraction, even though the BX QYs of NCs with a high “on” fraction vary dramatically. The BX QYs of single NCs are also weakly dependent upon excitation wavelength. The weak correlation between exciton “on” fractions and BX QYs suggests that multiple recombination processes are involved in the BX recombination. To explain our results, we propose a model that combines both trapping and an Auger mechanism for BX recombination.
Co-reporter:Jungmin Lee, Armon Sharei, Woo Young Sim, Andrea Adamo, Robert Langer, Klavs F. Jensen, and Moungi G. Bawendi
Nano Letters 2012 Volume 12(Issue 12) pp:6322-6327
Publication Date(Web):November 12, 2012
DOI:10.1021/nl303421h
The ability to straightforwardly deliver engineered nanoparticles into the cell cytosol with high viability will vastly expand the range of biological applications. Nanoparticles could potentially be used as delivery vehicles or as fluorescent sensors to probe the cell. In particular, quantum dots (QDs) may be used to illuminate cytosolic proteins for long-term microscopy studies. Whereas recent advances have been successful in specifically labeling proteins with QDs on the cell membrane, cytosolic delivery of QDs into live cells has remained challenging. In this report, we demonstrate high throughput delivery of QDs into live cell cytoplasm using an uncomplicated microfluidic device while maintaining cell viabilities of 80–90%. We verify that the nanoparticle surface interacts with the cytosolic environment and that the QDs remain nonaggregated so that single QDs can be observed.
Co-reporter:He Wei, Numpon Insin, Jungmin Lee, Hee-Sun Han, Jose M. Cordero, Wenhao Liu, and Moungi G. Bawendi
Nano Letters 2012 Volume 12(Issue 1) pp:22-25
Publication Date(Web):December 20, 2011
DOI:10.1021/nl202721q
The potential of superparamagnetic iron oxide nanoparticles (SPIONs) in various biomedical applications, including magnetic resonance imaging (MRI), sensing, and drug delivery, requires that their surface be derivatized to be hydrophilic and biocompatible. We report here the design and synthesis of a compact and water-soluble zwitterionic dopamine sulfonate (ZDS) ligand with strong binding affinity to SPIONs. After ligand exchange, the ZDS-coated SPIONs exhibit small hydrodynamic diameters, and stability with respect to time, pH, and salinity. Furthermore, small ZDS coated SPIONs were found to have a reduced nonspecific affinity (compared to negatively charged SPIONs) toward serum proteins; streptavidin/dye functionalized SPIONs were bioactive and thus specifically targeted biotin receptors.
Co-reporter:Daniel K. Harris
Journal of the American Chemical Society 2012 Volume 134(Issue 50) pp:20211-20213
Publication Date(Web):December 10, 2012
DOI:10.1021/ja309863n
The synthesis of III–V quantum dots has been long known to be more challenging than the synthesis of other types of inorganic quantum dots. This is attributed to highly reactive group-V precursors. We synthesized molecules that are suitable for use as group-V precursors and characterized their reactivity using multiple complementary techniques. We show that the size distribution of indium arsenide quantum dots indeed improves with decreased precursor reactivity.
Co-reporter:Rebecca C. Somers, Ryan M. Lanning, Preston T. Snee, Andrew B. Greytak, Rakesh K. Jain, Moungi G. Bawendi and Daniel G. Nocera
Chemical Science 2012 vol. 3(Issue 10) pp:2980-2985
Publication Date(Web):26 Jun 2012
DOI:10.1039/C2SC20212C
A ratiometric fluorescent pH sensor based on CdSe/CdZnS nanocrystal quantum dots (NCs) has been designed for biological pH ranges. The construct is formed from the conjugation of a pH dye (SNARF) to NCs coated with a poly(amido amine) (PAMAM) dendrimer. The sensor exhibits a well-resolved ratio response at pH values between 6 and 8 under linear or two-photon excitation, and in the presence of a 4% bovine serum albumin (BSA) solution.
Co-reporter:Andrew B. Greytak, Peter M. Allen, Wenhao Liu, Jing Zhao, Elizabeth R. Young, Zoran Popović, Brian J. Walker, Daniel G. Nocera and Moungi G. Bawendi
Chemical Science 2012 vol. 3(Issue 6) pp:2028-2034
Publication Date(Web):10 Apr 2012
DOI:10.1039/C2SC00561A
We report single-particle photoluminescence (PL) intermittency (blinking) with high on-time fractions in colloidal CdSe quantum dots (QD) with conformal CdS shells of 1.4 nm thickness, equivalent to approximately 4 CdS monolayers. All QDs observed displayed on-time fractions >60% with the majority >80%. The high on-time fraction blinking is accompanied by fluorescence quantum yields (QY) close to unity (up to 98% in an absolute QY measurement) when dispersed in organic solvents and a monoexponential ensemble photoluminescence (PL) decay lifetime. The CdS shell is formed in high synthetic yield using a modified selective ion layer adsorption and reaction (SILAR) technique that employs a silylated sulfur precursor. The CdS shell provides sufficient chemical and electronic passivation of the QD excited state to permit water solubilization with greater than 60% QY via ligand exchange with an imidazole-bearing hydrophilic polymer.
Co-reporter:Rebecca C. Somers, Preston T. Snee, Moungi G. Bawendi, Daniel G. Nocera
Journal of Photochemistry and Photobiology A: Chemistry 2012 Volume 248() pp:24-29
Publication Date(Web):15 November 2012
DOI:10.1016/j.jphotochem.2012.07.012
Energy transfer between a CdSe/ZnS nanocrystal (NC) donor and a rhodamine isothiocyanate (RITC) acceptor has been achieved via a functionalized poly(acrylic acid) (PAA) encapsulating layer over the surface of the NC. The modification of PAA with both N-octylamine (OA) and 5-amino-1-pentanol (AP) [PAA–OA–AP], allows for the simultaneous water-solubilization and functionalization of the NCs, underscoring the ease of synthesizing NC–acceptor conjugates with this strategy. Photophysical studies of the NC–RITC constructs showed that energy transfer is efficient, with kFRET approaching 108 s−1. The ease of the covalent conjugation of molecules to NCs with PAA–OA–AP coating, together with efficient energy transfer, makes the NCs encapsulated with PAA–OA–AP attractive candidates for sensing applications.Graphical abstractThe modification of poly(acrylic acid) (PAA) with both N-octylamine (OA) and 5-amino-1-4 pentanol (AP) [PAA–OA–AP] allows for the simultaneous water-solubilization and 5 functionalization of the NCs for applications derived from energy transfer.Highlights► Poly(acrylic acid) (PAA) has been modified with both N-octylamine (OA) and 5-amino-1-pentanol (AP) [PAA–OA–AP]. ► This modification furnishes a water-soluble and functionalized overcoating for conjugation to CdSe/ZnS nanocrystals (NCs). ► Photophysical studies establish energy transfer between the NC and a conjugated rhodamine isothiocyanate (RITC) dye. ► These properties together establish NC–PAA–OA–AP conjugates as attractive candidates for sensing applications.
Co-reporter:Gautham Nair, Jing Zhao, and Moungi G. Bawendi
Nano Letters 2011 Volume 11(Issue 3) pp:1136-1140
Publication Date(Web):February 2, 2011
DOI:10.1021/nl104054t
Biexciton properties strongly affect the usability of a light emitter in quantum photon sources and lasers but are difficult to measure for single fluorophores at room temperature due to luminescence intermittency and bleaching at the high excitation fluences usually required. Here, we observe the biexciton (BX) to exciton (X) to ground photoluminescence cascade of single colloidal semiconductor nanocrystals (NCs) under weak excitation in a g(2) photon correlation measurement and show that the normalized amplitude of the cascade feature is equal to the ratio of the BX to X fluorescence quantum yields. This imposes a limit on the attainable depth of photon antibunching and provides a robust means to study single emitter biexciton physics. In NC samples, we show that the BX quantum yield is considerably inhomogeneous, consistent with the defect sensitivity expected of the Auger nonradiative recombination mechanism. The method can be extended to study X,BX spectral and polarization correlations.
Co-reporter:Gautham Nair, Liang-Yi Chang, Scott M. Geyer, and Moungi G. Bawendi
Nano Letters 2011 Volume 11(Issue 5) pp:2145-2151
Publication Date(Web):April 18, 2011
DOI:10.1021/nl200798x
This article presents a perspective on the experimental and theoretical work to date on the efficiency of carrier multiplication (CM) in colloidal semiconductor nanocrystals (NCs). Early reports on CM in NCs suggested large CM efficiency enhancements. However, recent experiments have shown that CM in nanocrystalline samples is not significantly stronger, and often is weaker, than in the parent bulk when compared on an absolute photon energy basis. This finding is supported by theoretical consideration of the CM process and the competing intraband relaxation. We discuss the experimental artifacts that may have led to the apparently strong CM estimated in early reports. The finding of bulklike CM in NCs suggests that the main promise of quantum confinement is to boost the photovoltage at which carriers can be extracted. With this in mind, we discuss research directions that may result in effective use of CM in a solar cell.
Co-reporter:Brian J. Walker, August Dorn, Vladimir Bulović, and Moungi G. Bawendi
Nano Letters 2011 Volume 11(Issue 7) pp:2655-2659
Publication Date(Web):May 26, 2011
DOI:10.1021/nl200679n
J-aggregates are ordered clusters of coherently coupled molecular dyes,(1) and they have been used as light sensitizers in film photography due to their intense absorptions. Hybrid structures containing J-aggregates may also have applications in devices that require spectral specificity, such as color imaging or optical signaling.(2) However the use of J-aggregates in optoelectronic devices has posed a long-standing challenge(3, 4) due to the difficulty of controlling aggregate formation and the low charge carrier mobility of many J-aggregates in solid state. In this paper, we demonstrate a modular method to assemble three different cyanine J-aggregates onto CdSe nanowires, resulting in a photodetector that is color-sensitized in three specific, narrow absorption bands. Both the J-aggregate and nanowire device components are fabricated from solution and the sensitizing wavelength is switched from blue to red to green, using only solution-phase exchange of the J-aggregates on the same underlying device.
Co-reporter:Daniel K. Harris ; Peter M. Allen ; Hee-Sun Han ; Brian J. Walker ; Jungmin Lee
Journal of the American Chemical Society 2011 Volume 133(Issue 13) pp:4676-4679
Publication Date(Web):March 9, 2011
DOI:10.1021/ja1101932
We present the synthesis of Cd3As2 colloidal quantum dots luminescent from 530 to 2000 nm. Previous reports on quantum dots emitting in the infrared are primarily limited to the lead chalcogenides and indium arsenide. This work expands the availability of high quality infrared emitters.
Co-reporter:Vikash P. Chauhan;Dr. Zoran Popovi&x107;;Dr. Ou Chen;Jian Cui;Dr. Dai Fukumura;Dr. Moungi G. Bawendi;Dr. Rakesh K. Jain
Angewandte Chemie 2011 Volume 123( Issue 48) pp:11619-11622
Publication Date(Web):
DOI:10.1002/ange.201104449
Co-reporter:Cliff Wong;Triantafyllos Stylianopoulos;Jian Cui;Vikash P. Chauhan;Wen Jiang;John Martin;Zoran Popović;Rakesh K. Jain;Dai Fukumura
PNAS 2011 Volume 108 (Issue 6 ) pp:2426-2431
Publication Date(Web):2011-02-08
DOI:10.1073/pnas.1018382108
Current Food and Drug Administration-approved cancer nanotherapeutics, which passively accumulate around leaky regions of
the tumor vasculature because of an enhanced permeation and retention (EPR) effect, have provided only modest survival benefits.
This suboptimal outcome is likely due to physiological barriers that hinder delivery of the nanotherapeutics throughout the
tumor. Many of these nanotherapeutics are ≈100 nm in diameter and exhibit enhanced accumulation around the leaky regions of
the tumor vasculature, but their large size hinders penetration into the dense collagen matrix. Therefore, we propose a multistage
system in which 100-nm nanoparticles “shrink” to 10-nm nanoparticles after they extravasate from leaky regions of the tumor
vasculature and are exposed to the tumor microenvironment. The shrunken nanoparticles can more readily diffuse throughout
the tumor's interstitial space. This size change is triggered by proteases that are highly expressed in the tumor microenvironment
such as MMP-2, which degrade the cores of 100-nm gelatin nanoparticles, releasing smaller 10-nm nanoparticles from their surface.
We used quantum dots (QD) as a model system for the 10-nm particles because their fluorescence can be used to demonstrate
the validity of our approach. In vitro MMP-2 activation of the multistage nanoparticles revealed that the size change was
efficient and effective in the enhancement of diffusive transport. In vivo circulation half-life and intratumoral diffusion
measurements indicate that our multistage nanoparticles exhibited both the long circulation half-life necessary for the EPR
effect and the deep tumor penetration required for delivery into the tumor's dense collagen matrix.
Co-reporter:Jinyoung Baek;Dr. Peter M. Allen; Moungi G. Bawendi; Klavs F. Jensen
Angewandte Chemie 2011 Volume 123( Issue 3) pp:653-656
Publication Date(Web):
DOI:10.1002/ange.201006412
Co-reporter:Jinyoung Baek;Dr. Peter M. Allen; Moungi G. Bawendi; Klavs F. Jensen
Angewandte Chemie International Edition 2011 Volume 50( Issue 3) pp:627-630
Publication Date(Web):
DOI:10.1002/anie.201006412
Co-reporter:Vikash P. Chauhan;Dr. Zoran Popovi&x107;;Dr. Ou Chen;Jian Cui;Dr. Dai Fukumura;Dr. Moungi G. Bawendi;Dr. Rakesh K. Jain
Angewandte Chemie International Edition 2011 Volume 50( Issue 48) pp:11417-11420
Publication Date(Web):
DOI:10.1002/anie.201104449
Co-reporter:Scott M. Geyer, Jennifer M. Scherer, Nosipho Moloto, Frank B. Jaworski, and Moungi G. Bawendi
ACS Nano 2011 Volume 5(Issue 7) pp:5566
Publication Date(Web):May 17, 2011
DOI:10.1021/nn2010238
A colloidal quantum dot (QD) luminescent down-shifting (LDS) layer is used to sensitize an InGaAs short wavelength infrared photodetector to the near UV spectral band. An average improvement in the external quantum efficiency (EQE) from 1.8% to 21% across the near UV is realized using an LDS layer consisting of PbS/CdS core/shell QDs embedded in PMMA. A simple model is used to fit the experimental EQE data. A UV sensitive InGaAs imaging array is demonstrated and the effect of the LDS layer on the optical resolution is calculated. The bandwidth of the LDS detector under UV illumination is characterized and shown to be determined by the photoluminescence lifetime of the QDs.Keywords: down-shifting; dual-band; InGaAs; nanocrystal; quantum dot; SWIR
Co-reporter:Brian J. Walker, Vladimir Bulović, and Moungi G. Bawendi
Nano Letters 2010 Volume 10(Issue 10) pp:3995-3999
Publication Date(Web):September 23, 2010
DOI:10.1021/nl1018639
This paper describes the solution preparation of thin films composed of quantum dots and thiacyanine J-aggregates, making use of the size tunable emission of quantum dots and the narrow, intense absorption of J-aggregates in the solid state. These blended films exhibit 90% energy transfer efficiency from J-aggregates to quantum dots and can uniformly cover a large area. Because the presence of the J-aggregates enhances the QD photoluminescence intensity by 2.5-fold over QDs alone, these solid state materials may be useful in downconversion applications or in fundamental investigations of light harvesting.
Co-reporter:Hee-Sun Han ; Neal K. Devaraj ; Jungmin Lee ; Scott A. Hilderbrand ; Ralph Weissleder
Journal of the American Chemical Society 2010 Volume 132(Issue 23) pp:7838-7839
Publication Date(Web):May 19, 2010
DOI:10.1021/ja101677r
We present a bioorthogonal and modular conjugation method for efficient coupling of organic dyes and biomolecules to quantum dots (QDs) using a norbornene−tetrazine cycloaddition. The use of noncoordinating functional groups combined with the rapid rate of the cycloaddition leads to highly efficient conjugation. We have applied this method to the in situ targeting of norbornene-coated QDs to live cancer cells labeled with tetrazine-modified proteins.
Co-reporter:PeterM. Allen;BrianJ. Walker;MoungiG. Bawendi
Angewandte Chemie 2010 Volume 122( Issue 4) pp:772-774
Publication Date(Web):
DOI:10.1002/ange.200905632
Co-reporter:PeterM. Allen;BrianJ. Walker;MoungiG. Bawendi
Angewandte Chemie International Edition 2010 Volume 49( Issue 4) pp:760-762
Publication Date(Web):
DOI:10.1002/anie.200905632
Co-reporter:Dr. Zoran Popovi&x107;;Dr. Wenhao Liu;Vikash P. Chauhan;Jungmin Lee;Cliff Wong;Dr. Andrew B. Greytak;Numpon Insin;Dr. Daniel G. Nocera;Dr. Dai Fukumura;Dr. Rakesh K. Jain;Dr. Moungi G. Bawendi
Angewandte Chemie International Edition 2010 Volume 49( Issue 46) pp:8649-8652
Publication Date(Web):
DOI:10.1002/anie.201003142
Co-reporter:Dr. Zoran Popovi&x107;;Dr. Wenhao Liu;Vikash P. Chauhan;Jungmin Lee;Cliff Wong;Dr. Andrew B. Greytak;Numpon Insin;Dr. Daniel G. Nocera;Dr. Dai Fukumura;Dr. Rakesh K. Jain;Dr. Moungi G. Bawendi
Angewandte Chemie 2010 Volume 122( Issue 46) pp:8831-8834
Publication Date(Web):
DOI:10.1002/ange.201003142
Co-reporter:Scott M. Geyer, Peter M. Allen, Liang-Yi Chang, Cliff R. Wong, Tim P. Osedach, Ni Zhao, Vladimir Bulovic, and Moungi G. Bawendi
ACS Nano 2010 Volume 4(Issue 12) pp:7373
Publication Date(Web):December 2, 2010
DOI:10.1021/nn101772n
Nanocrystal (NC) films have been proposed as an alternative to bulk semiconductors for electronic applications such as solar cells and photodetectors. One outstanding challenge in NC electronics is to robustly control the carrier type to create stable p−n homojunction-based devices. We demonstrate that the postsynthetic addition of Cd to InAs nanocrystals switches the resulting InAs:Cd NC films from n-type to p-type when operating in a field effect transistor. This method presents a stable, facile way to control the carrier type of InAs nanocrystals prior to deposition. We present two mechanisms to explain the observed switch in carrier type. In mechanism 1, Cd atoms are incorporated at In sites in the lattice and act as acceptor defects, forming a partially compensated p-type semiconductor. In mechanism 2, Cd atoms passivate donor-type InAs surface states and create acceptor-type surface states. This work represents a critical step toward the creation of p−n homojunction-based NC electronics.Keywords: InAs; nanocrystal; photoconductivity; quantum dot
Co-reporter:Hak Soo Choi, Binil Itty Ipe, Preeti Misra, Jeong Heon Lee, Moungi G. Bawendi and John V. Frangioni
Nano Letters 2009 Volume 9(Issue 6) pp:2354-2359
Publication Date(Web):May 7, 2009
DOI:10.1021/nl900872r
A significant portion of the field of nanomedicine is predicated on being able to target nanoparticles to sites of disease. However, in vivo biodistribution and clearance of nanoparticles are poorly understood. In this study, a novel formulation of near-infrared fluorescent InAs(ZnS) quantum dots was synthesized and coated with a systematically increasing chain length of PEG. We found that varying PEG chain length resulted in major changes in organ/tissue-selective biodistribution and clearance from the body.
Co-reporter:Peter M. Allen ; Wenhao Liu ; Vikash P. Chauhan ; Jungmin Lee ; Alice Y. Ting ; Dai Fukumura ; Rakesh K. Jain
Journal of the American Chemical Society 2009 Volume 132(Issue 2) pp:470-471
Publication Date(Web):December 21, 2009
DOI:10.1021/ja908250r
We present the synthesis of InAs quantum dots (QDs) with a ZnCdS shell with bright and stable emission in the near-infrared (NIR, 700−900 nm) region for biological imaging applications. We demonstrate how NIR QDs can image tumor vasculature in vivo at significantly deeper penetration depths and with higher contrast than visible emitting CdSe(CdS) QDs. Targeted cellular labeling is also presented and may enable multiplexed and low autofluorescence cellular imaging.
Co-reporter:Brian J. Walker ; Gautham P. Nair ; Lisa F. Marshall ; Vladimir Bulović
Journal of the American Chemical Society 2009 Volume 131(Issue 28) pp:9624-9625
Publication Date(Web):June 23, 2009
DOI:10.1021/ja902813q
We report narrow-band absorption enhancement of semiconductor nanocrystals via Förster resonance energy transfer from cyanine J-aggregates. These J-aggregated dyes associate electrostatically with short quantum-dot (QD) surface ligands in solution. Energy transfer efficiencies approach unity for this light sensitization and result in a 5-fold enhancement in the QD excitation near the J-aggregate absorption maximum. Because a thin layer of J-aggregates attenuates the same amount of light (at peak absorbance) as a far thicker film of monomer dye, these absorption-enhanced materials may have applications in light-sensitizing applications such as photodetection and optical down-conversion.
Co-reporter:Emily J. McLaurin ; Andrew B. Greytak ; Moungi G. Bawendi ;Daniel G. Nocera
Journal of the American Chemical Society 2009 Volume 131(Issue 36) pp:12994-13001
Publication Date(Web):August 21, 2009
DOI:10.1021/ja902712b
Two nanocrystal-osmium(II) polypyridyl (NC-Os(II)PP) conjugates have been designed to detect oxygen in biological environments. Polypyridines appended with a single free amine were linked with facility to a carboxylic acid functionality of a semiconductor NC overlayer to afford a biologically stable amide bond. The Os(II)PP complexes possess broad absorptions that extend into the red spectral region; this absorption feature makes them desirable acceptors of energy from NC donors. Fluorescence resonance energy transfer (FRET) from the NC to the Os(II)PP causes an enhanced Os(II)PP emission with a concomitant quenching of the NC emission. Owing to the large two-photon absorption cross-section of the NCs, FRET from the NC to the Os(II)PP can be established under two-photon excitation conditions. In this way, two-photon processes of metal polypyridyl complexes can be exploited for sensing. The emission of the NC is insensitive to oxygen, even at 1 atm, whereas excited states of both osmium complexes are quenched in the presence of oxygen. The NC emission may thus be used as an internal reference to correct for fluctuations in the photoluminescence intensity signal. These properties taken together establish NC-Os(II)PP conjugates as competent ratiometric, two-photon oxygen sensors for application in biological microenvironments.
Co-reporter:Jonathan E. Halpert, Jonathan R. Tischler, Gautham Nair, Brian J. Walker, Wenhao Liu, Vladimir Bulović and Moungi G. Bawendi
The Journal of Physical Chemistry C 2009 Volume 113(Issue 23) pp:9986-9992
Publication Date(Web):May 13, 2009
DOI:10.1021/jp8099169
We report the formation and photonic properties of CdSe/ZnS quantum dot (QD)/J-aggregate donor−acceptor Forster resonant energy transfer (FRET) pairs that are electrostatically bound and dispersed in water. Assembly occurs when the positively charged dye, 1,1′,3,3′-tetraethyl-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine (TTBC), binds electrostatically to QDs that are coated with a negatively charged amphiphilic polymer. QD/J-aggregate FRET pairs display the broadband absorption in the visible and the ultraviolet (UV) part of the spectrum typical of quantum dots, along with the narrow emission linewidths characteristic of J-band emitters (∼12 nm full width at half-maximum). We use dynamic light scattering, transmission electron microscopy, photoluminescence spectroscopy, and photoluminescence lifetimes to conclude that the size of the aggregates formed in the presence of QDs is between 1−6 nm. We find the FRET radius of the QD/J-aggregate to be 5.1 nm. We further demonstrate electrostatic binding as a general synthetic strategy for these types of FRET pairs by attaching a negatively charged J-aggregate (BIC) to a quantum dot coated with positively charged ligands.
Co-reporter:Samuel Marre;Jongnam Park;Jane Rempel;Juan Guan;Klavs F. Jensen
Advanced Materials 2008 Volume 20( Issue 24) pp:4830-4834
Publication Date(Web):
DOI:10.1002/adma.200801579
Co-reporter:August Dorn, Hao Huang and Moungi G. Bawendi
Nano Letters 2008 Volume 8(Issue 5) pp:1347-1351
Publication Date(Web):April 8, 2008
DOI:10.1021/nl080018o
We present a technique for making nanoscale gaps with work function offsets based on electromigrating leads composed of two different metals. Electroluminescence spectra from plain metal gaps with and without CdSe/ZnS (core/shell) nanocrystals are qualitatively very similar and exhibit features that are much broader than the photoluminescence spectra obtained from the same nanocrystals. These observations can be explained by inelastic scattering of conduction electrons in the metal leads or by electroluminescence from small metallic clusters that can form during the fabrication process. However, electroluminescence that spectrally coincides with nanocrystal photoluminescence can be observed in devices containing nanocrystals formed by electromigrating Pt leads bridged with small indium islands. This suggests that electromigrating leads made of different metals is a promising route to fabricating nanoscale gaps with work function offsets for optoelectronic devices.
Co-reporter:Numpon Insin, Joseph B. Tracy, Hakho Lee, John P. Zimmer, Robert M. Westervelt, Moungi G. Bawendi
ACS Nano 2008 Volume 2(Issue 2) pp:197
Publication Date(Web):January 10, 2008
DOI:10.1021/nn700344x
We describe the synthesis of magnetic and fluorescent silica microspheres fabricated by incorporating maghemite (γ-Fe2O3) nanoparticles (MPs) and CdSe/CdZnS core/shell quantum dots (QDs) into a silica shell around preformed silica microspheres. The resultant ∼500 nm microspheres have a narrow size distribution and show uniform incorporation of QDs and MPs into the shell. We have demonstrated manipulation of these microspheres using an external magnetic field with real-time fluorescence microscopy imaging.Keywords: fluorescent; iron oxide nanoparticles; magnetic manipulation; multifunctional microspheres; quantum dots; silica microspheres; superparamagnetic
Co-reporter:Jonathan S. Steckel Dr.;Preston Snee Dr.;Seth Coe-Sullivan Dr.;John P. Zimmer Dr.;Jonathan E. Halpert;Polina Anikeeva;Lee-Ann Kim;Vladimir Bulovic
Angewandte Chemie 2006 Volume 118(Issue 35) pp:
Publication Date(Web):28 JUL 2006
DOI:10.1002/ange.200600317
Durch und durch grün: Nanokristalle mit einem CdxZn1−xSe-Kern wurden synthetisiert und mit CdyZn1−yS überzogen, um Kern-Schale-Nanokristalle mit der idealen Emissionswellenlänge für Quantenpunkt-LEDs (QD-LEDs) zu erhalten. Diese (CdxZn1−xSe)CdyZn1−yS-Kern-Schale-Nanokristalle wurden zur Herstellung farbgesättigter grün emittierender QD-LEDs genutzt (siehe Bild), die sich für Display-Anwendungen eignen.
Co-reporter:Jonathan S. Steckel Dr.;Preston Snee Dr.;Seth Coe-Sullivan Dr.;John P. Zimmer Dr.;Jonathan E. Halpert;Polina Anikeeva;Lee-Ann Kim;Vladimir Bulovic
Angewandte Chemie International Edition 2006 Volume 45(Issue 35) pp:
Publication Date(Web):28 JUL 2006
DOI:10.1002/anie.200600317
Green to the core: CdxZn1−xSe alloy core nanocrystals are synthesized and overcoated with CdyZn1−yS to create core–shell nanocrystals with the ideal wavelength of emission for quantum dot light-emitting device (QD-LED) displays. These (CdxZn1−xSe)CdyZn1−yS core–shell nanocrystals are used to fabricate color-saturated green-emitting QD-LEDs (see picture), which are suitable for display applications.
Co-reporter:P. T. Snee;Y. Chan;D. G. Nocera;M. G. Bawendi
Advanced Materials 2005 Volume 17(Issue 9) pp:
Publication Date(Web):10 MAR 2005
DOI:10.1002/adma.200401571
Spherical whispering-gallery-mode lasers employing CdSe/ZnS semiconductor nanocrystals (see Figure, inset scale bar: 15 μm) are assembled on a substrate using a simple, robust spin-coating fabrication method. The flexibility to choose the size of the microsphere template and the emission wavelength allows for the observation of single-mode lasing. At higher excitation intensities, lasing from higher multiexcitonic states is also observed.
Co-reporter:Brian K. H. Yen;Axel Günther;Martin A. Schmidt ;Klavs F. Jensen
Angewandte Chemie International Edition 2005 Volume 44(Issue 34) pp:
Publication Date(Web):20 JUN 2005
DOI:10.1002/anie.200500792
Monodisperse CdSe quantum dots (QDs) with excellent optical properties can be prepared with a gas–liquid segmented flow microreactor with multiple temperature zones (see picture; red=heated; blue=cooled quench zone). The enhanced mixing and narrow residence time distributions of segmented flow produce QDs superior to those prepared in single-phase operations.
Co-reporter:Brian K. H. Yen;Axel Günther;Martin A. Schmidt ;Klavs F. Jensen
Angewandte Chemie International Edition 2005 Volume 44(Issue 34) pp:
Publication Date(Web):22 AUG 2005
DOI:10.1002/anie.200590114
Co-reporter:Brian K. H. Yen;Axel Günther;Martin A. Schmidt ;Klavs F. Jensen
Angewandte Chemie 2005 Volume 117(Issue 34) pp:
Publication Date(Web):20 JUN 2005
DOI:10.1002/ange.200500792
Monodisperse CdSe-Quantenpunkte (QDs) mit ausgezeichneten optischen Eigenschaften sind mit einem Gas-flüssig-segmentierten Fluss-Mikroreaktor erhältlich, der mehrere Temperaturzonen aufweist (siehe Bild; rot=beheizte, blau=gekühlte Quenching-Zone). Das bessere Mischen und die engen Verweilzeitverteilungen des segmentierten Flusses liefern QDs, die denen aus Einphasenoperationen überlegen sind.
Co-reporter:Brian K. H. Yen;Axel Günther;Martin A. Schmidt ;Klavs F. Jensen
Angewandte Chemie 2005 Volume 117(Issue 34) pp:
Publication Date(Web):22 AUG 2005
DOI:10.1002/ange.200590113
Co-reporter:Y. Chan;J. P. Zimmer;M. Stroh;J. S. Steckel;R. K. Jain;M. G. Bawendi
Advanced Materials 2004 Volume 16(Issue 23‐24) pp:
Publication Date(Web):17 NOV 2004
DOI:10.1002/adma.200400237
Silica microspheres coated with a silica or titania shell containing fluorescent semiconductor nanocrystals are described. Since the coating process does not affect the monodispersity of the silica microspheres, microspheres of a defined size and emission wavelength, potentially useful for biological applications, can be fabricated. The Figure shows 100 nm diameter blue-light-emitting and 500 nm diameter red-light-emitting microspheres circulating in the brain of a mouse.
Co-reporter:Jonathan S. Steckel;John P. Zimmer;Seth Coe-Sullivan;Nathan E. Stott;Vladimir Bulović
Angewandte Chemie International Edition 2004 Volume 43(Issue 16) pp:
Publication Date(Web):6 APR 2004
DOI:10.1002/anie.200453728
Out of the blue: (CdS)ZnS nanocrystals suitable for display applications have been prepared and exhibit a narrow, blue luminescence from 460 to 480 nm (FWHM ≤28 nm; see picture), with quantum efficiencies of 20–30 %. It is possible to demonstrate blue electroluminescence from these core–shell nanocrystals by embedding them in an organic thin-film device.
Co-reporter:Jonathan S. Steckel;John P. Zimmer;Seth Coe-Sullivan;Nathan E. Stott;Vladimir Bulović
Angewandte Chemie 2004 Volume 116(Issue 16) pp:
Publication Date(Web):6 APR 2004
DOI:10.1002/ange.200453728
Ins Blaue: Die hier vorgestellten (CdS)ZnS-Nanokristalle für Displays zeichnen sich durch eine blaue Lumineszenz im engen Bereich zwischen 460 und 480 nm (Halbwertsbreite≤28 nm; siehe Bild) mit einer Quanteneffizienz von 20–30 % aus. Nach Integrierung in dünnen organischen Filmen kann blaue Elektrolumineszenz dieser Kern-Schale-Nanokristalle ausgelöst werden.
Co-reporter:B.K.H. Yen;N.E. Stott;K.F. Jensen;M.G. Bawendi
Advanced Materials 2003 Volume 15(Issue 21) pp:
Publication Date(Web):11 SEP 2003
DOI:10.1002/adma.200305162
Co-reporter:J.S. Steckel;S. Coe-Sullivan;V. Bulović;M.G. Bawendi
Advanced Materials 2003 Volume 15(Issue 21) pp:
Publication Date(Web):6 NOV 2003
DOI:10.1002/adma.200305449
Co-reporter:W.-K. Woo;K.T. Shimizu;M.V. Jarosz;R.G. Neuhauser;C.A. Leatherdale;M.A. Rubner;M.G. Bawendi
Advanced Materials 2002 Volume 14(Issue 15) pp:
Publication Date(Web):29 JUL 2002
DOI:10.1002/1521-4095(20020805)14:15<1068::AID-ADMA1068>3.0.CO;2-1
Co-reporter:V.C. Sundar;H.-J. Eisler;M.G. Bawendi
Advanced Materials 2002 Volume 14(Issue 10) pp:
Publication Date(Web):17 MAY 2002
DOI:10.1002/1521-4095(20020517)14:10<739::AID-ADMA739>3.0.CO;2-Y
Co-reporter:Dmitry P. Dinega;M. G. Bawendi
Angewandte Chemie International Edition 1999 Volume 38(Issue 12) pp:
Publication Date(Web):8 JUN 1999
DOI:10.1002/(SICI)1521-3773(19990614)38:12<1788::AID-ANIE1788>3.0.CO;2-2
Kinetic control of crystal growth in the presence of a coordinating ligand is critical for the formation of a new structure of elemental cobalt (ε-cobalt, the unit cell with the two different types of cobalt atoms is shown), which was discovered upon analyzing the metallic powder produced by the thermal decomposition of [Co2(CO)8] in solution in the presence of trioctylphosphane oxide [TOPO, Eq. (1)].
Co-reporter:Dmitry P. Dinega
Angewandte Chemie 1999 Volume 111(Issue 12) pp:
Publication Date(Web):8 JUN 1999
DOI:10.1002/(SICI)1521-3757(19990614)111:12<1906::AID-ANGE1906>3.0.CO;2-0
Die kinetische Kontrolle des Kristallwachstums in Gegenwart eines koordinierenden Liganden spielt eine entscheidende Rolle bei der Bildung einer neuen Struktur elementaren Cobalts (ε-Cobalt, die Elementarzelle mit den zwei Arten von Cobaltatomen ist gezeigt). Diese wurde bei der Analyse des metallischen Pulvers entdeckt, das bei der thermischen Zersetzung von Octacarbonyldicobalt in Lösung in Gegenwart von Trioctylphosphanoxid (TOPO) entsteht [Gl. (1)].
Co-reporter:Camilla Lelii, Moungi G. Bawendi, Paolo Biagini, Po-Yen Chen, Marcello Crucianelli, Julio M. D'Arcy, Francesco De Angelis, Paula T. Hammond and Riccardo Po
Journal of Materials Chemistry A 2014 - vol. 2(Issue 43) pp:NaN18382-18382
Publication Date(Web):2014/08/29
DOI:10.1039/C4TA03098B
CdSe quantum dots of two different sizes exhibiting a maximum emission at 495 nm (CdSe495) and 545 nm (CdSe545) were combined with di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4-dicarboxylato)ruthenium(II) (N719) or 2-cyano-3-{5-[7-(4-diphenylamino-phenyl)benzo[1,2,5]thiadiazol-4-yl]-thiophen-2-yl}-acrylic acid (TBTCA) resulting in four novel hybrid organic–inorganic sensitizers, which were used in the fabrication of dye-sensitized solar cells. The results showed that with N719, both the CdSe dots decreased the power conversion efficiencies when compared to a standard device consisting only of N719 as the sensitizer. With the organic dye TBTCA, CdSe545 showed no significant effect, while CdSe495 interacted favorably, leading to a 25% increase in power conversion efficiency compared to a device sensitized solely by TBTCA. Studies on excited-state lifetimes of N719 in the presence of CdSe did not distinguish between energy and/or charge transfer mechanisms. On the other hand, time correlated single photon counting experiments on the photoelectrodes suggest that the advantages due to the CdSe495–TBTCA combination could be ascribed to FRET from quantum dots to the organic dye and to a further contribution, as suggested by IPCE spectra, consisting of electron transfer via cascade from the LUMO level of TBTCA to CdSe495 to TiO2, which produces a higher flux of electrons in the external circuit.
Co-reporter:Jian Cui, Andrew P. Beyler, Thomas S. Bischof, Mark W. B. Wilson and Moungi G. Bawendi
Chemical Society Reviews 2014 - vol. 43(Issue 4) pp:NaN1310-1310
Publication Date(Web):2013/11/27
DOI:10.1039/C3CS60330J
Prior to the advent of single-molecule fluorescence spectroscopy, many of the fundamental optical properties of colloidal semiconductor nanocrystal quantum dots were obscured by ensemble averaging over their inherent inhomogeneities. Single quantum dot spectroscopy has become a leading technique for the unambiguous determination of the governing excitonic physics of these quantum-confined systems. The analysis and interpretation of the timing and energies of photons emitted from individual nanocrystals have uncovered unexpected and fundamental electronic processes at the nanoscale. We review several different paradigms for deconstructing the photon stream from single nanocrystals, ranging from intensity “binning” techniques to more sophisticated methods based on single-photon counting. In particular, we highlight photon correlation – a powerful developing paradigm in single-nanocrystal studies. The application of photon-correlation techniques to single nanocrystals is changing the study of multiexcitonic recombination dynamics, uncovering the basic processes governing spectral linewidths and spectral diffusion, and enabling the extraction of single-nanocrystal properties directly from an ensemble with high statistical significance. These single-molecule techniques have proven invaluable for understanding the physics of nanocrystals and can provide unique insight into other heterogeneous and dynamical systems.
Co-reporter:Michel Nasilowski, Lea Nienhaus, Sophie N. Bertram and Moungi G. Bawendi
Chemical Communications 2017 - vol. 53(Issue 5) pp:NaN872-872
Publication Date(Web):2016/12/12
DOI:10.1039/C6CC07403K
Traditionally, PbS/CdS quantum dots (QDs) have been synthesized via a cation exchange method, making fine control over shell growth challenging. We show here that colloidal atomic layer deposition (c-ALD) allows for the sequential growth of single monolayers of the shell, thus creating a ‘true’ CdS shell on PbS QDs.
Co-reporter:Michel Nasilowski, Lea Nienhaus, Sophie N. Bertram and Moungi G. Bawendi
Chemical Communications 2017 - vol. 53(Issue 32) pp:NaN4517-4517
Publication Date(Web):2017/04/06
DOI:10.1039/C7CC90119D
Correction for ‘Colloidal atomic layer deposition growth of PbS/CdS core/shell quantum dots’ by Michel Nasilowski et al., Chem. Commun., 2017, 53, 869–872.
Co-reporter:Rebecca C. Somers, Ryan M. Lanning, Preston T. Snee, Andrew B. Greytak, Rakesh K. Jain, Moungi G. Bawendi and Daniel G. Nocera
Chemical Science (2010-Present) 2012 - vol. 3(Issue 10) pp:NaN2985-2985
Publication Date(Web):2012/06/26
DOI:10.1039/C2SC20212C
A ratiometric fluorescent pH sensor based on CdSe/CdZnS nanocrystal quantum dots (NCs) has been designed for biological pH ranges. The construct is formed from the conjugation of a pH dye (SNARF) to NCs coated with a poly(amido amine) (PAMAM) dendrimer. The sensor exhibits a well-resolved ratio response at pH values between 6 and 8 under linear or two-photon excitation, and in the presence of a 4% bovine serum albumin (BSA) solution.
Co-reporter:Andrew B. Greytak, Peter M. Allen, Wenhao Liu, Jing Zhao, Elizabeth R. Young, Zoran Popović, Brian J. Walker, Daniel G. Nocera and Moungi G. Bawendi
Chemical Science (2010-Present) 2012 - vol. 3(Issue 6) pp:NaN2034-2034
Publication Date(Web):2012/04/10
DOI:10.1039/C2SC00561A
We report single-particle photoluminescence (PL) intermittency (blinking) with high on-time fractions in colloidal CdSe quantum dots (QD) with conformal CdS shells of 1.4 nm thickness, equivalent to approximately 4 CdS monolayers. All QDs observed displayed on-time fractions >60% with the majority >80%. The high on-time fraction blinking is accompanied by fluorescence quantum yields (QY) close to unity (up to 98% in an absolute QY measurement) when dispersed in organic solvents and a monoexponential ensemble photoluminescence (PL) decay lifetime. The CdS shell is formed in high synthetic yield using a modified selective ion layer adsorption and reaction (SILAR) technique that employs a silylated sulfur precursor. The CdS shell provides sufficient chemical and electronic passivation of the QD excited state to permit water solubilization with greater than 60% QY via ligand exchange with an imidazole-bearing hydrophilic polymer.
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