Showing papers on "Quantum dot published in 2010"

Atomically thin MoS2: a new direct-gap semiconductor

Abstract: The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N=1,2,…,6 S-Mo-S monolayers have been investigated by optical spectroscopy Through characterization by absorption, photoluminescence, and photoconductivity spectroscopy, we trace the effect of quantum confinement on the material's electronic structure With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by more than 06 eV This leads to a crossover to a direct-gap material in the limit of the single monolayer Unlike the bulk material, the MoS₂ monolayer emits light strongly The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 10⁴ compared with the bulk material

Emerging Photoluminescence in Monolayer MoS2

Abstract: Novel physical phenomena can emerge in low-dimensional nanomaterials. Bulk MoS2, a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS2 crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d-electron system. This observation shows that quantum confinement in layered d-electron materials like MoS2 provides new opportunities for engineering the electronic structure of matter at the nanoscale.

Unidirectional emission of a quantum dot coupled to a nanoantenna

Abstract: Nanoscale quantum emitters are key elements in quantum optics and sensing. However, efficient optical excitation and detection of such emitters involves large solid angles because their interaction with freely propagating light is omnidirectional. Here, we present unidirectional emission of a single emitter by coupling to a nanofabricated Yagi-Uda antenna. A quantum dot is placed in the near field of the antenna so that it drives the resonant feed element of the antenna. The resulting quantum-dot luminescence is strongly polarized and highly directed into a narrow forward angular cone. The directionality of the quantum dot can be controlled by tuning the antenna dimensions. Our results show the potential of optical antennas to communicate energy to, from, and between nano-emitters.

Nanoparticles : from theory to application

Abstract: 1. General Introduction (G. Schmid).2. Quantum Dots (W. Parak, et al.).Introduction and Outline.Nanoscale Materials and Quantum Mechanics.From Atoms to Molecules and Quantum Dots.Shrinking Bulk Materials to a Quantum Dot.Energy Levels of a (Semiconductor) Quantum Dot.Varieties of Quantum Dots.Optical Properties of Quantum Dots.Some (Electrical) Transport Properties of Quantum Dots.3. Syntheses and Characterizations.Semiconductor Nanoparticles.Synthesis of Metal Nanoparticles.4. Organization of Nanoparticles.Semiconductor Nanoparticles.Metal Nanoparticles.5. Properties.Semiconductor Nanoparticles.Electrical Properties of Metal Nanoparticles.6. Biomaterial-Nanoparticle Hybrid Systems: Synthesis, Properties, and Applications (E. Katz, et al.).Introduction.The Synthesis and Properties of Biomaterial-Functionalized Nanoparticles.Biomaterial-Functionalized for Controlled Chemical Reactivity.The Aggregation of Biomaterial-Functionalized Nanoparticles.Assembly of Biomaterial-Nanoparticles Architectures on Surfaces.Functional Biomaterial-Nanoparticle Structures on Surfaces for Sensoric and Electronic Applications.Biomaterial-Functionalized Magnetic Particles.7. Conclusions and Perspectives (All Authors).

Near-Infrared Localized Surface Plasmon Resonances Arising from Free Carriers in Doped Quantum Dots

Abstract: Quantum confinement of electronic wavefunctions in semiconductor quantum dots (QDs) yields discrete atom-like and tunable electronic levels, thereby allowing the engineering of excitation and emission spectra. Metal nanoparticles, on the other hand, display strong resonant interactions with light from localized surface plasmon resonance (LSPR) oscillations of free carriers, resulting in enhanced and geometrically tunable absorption and scattering resonances. The complementary attributes of these nanostructures lends strong interest toward integration into hybrid nanostructures to explore enhanced properties or the emergence of unique attributes arising from their interaction. However, the physicochemical interface between the two components can be limiting for energy transfer and synergistic coupling within such a hybrid nanostructure. Therefore, it is advantageous to realize both attributes, i.e., LSPRs and quantum confinement within the same nanostructure. Here, we describe well-defined LSPRs arising from p-type carriers in vacancy-doped semiconductor quantum dots. This opens up possibilities for light harvesting, non-linear optics, optical sensing and manipulation of solid-state processes in single nanocrystals.

Semiconductor quantum dots and quantum dot arrays and applications of multiple exciton generation to third-generation photovoltaic solar cells.

Abstract: Here, we will first briefly summarize the general principles of QD synthesis using our previous work on InP as an example. Then we will focus on QDs of the IV-VI Pb chalcogenides (PbSe, PbS, and PbTe) and Si QDs because these were among the first QDs that were reported to produce multiple excitons upon absorbing single photons of appropriate energy (a process we call multiple exciton generation (MEG)). We note that in addition to Si and the Pb-VI QDs, two other semiconductor systems (III-V InP QDs(56) and II-VI core-shell CdTe/CdSe QDs(57)) were very recently reported to also produce MEG. Then we will discuss photogenerated carrier dynamics in QDs, including the issues and controversies related to the cooling of hot carriers and the magnitude and significance of MEG in QDs. Finally, we will discuss applications of QDs and QD arrays in novel quantum dot PV cells, where multiple exciton generation from single photons could yield significantly higher PV conversion efficiencies.

Quantum Dots and Their Multimodal Applications: A Review

Abstract: Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

White‐Light‐Emitting Diodes with Quantum Dot Color Converters for Display Backlights

Abstract: Quantum dots (QDs) have attracted great attention as good candidate for the next generation displays due to their narrow emission, and high luminescence efficiency, and tunable emission covering all visible range. However, QDs easily lost their initial optical properties during the process for a device fabrication and practical operation. We synthesized well passivated green and red light emitting QDs that show almost 100% of QE. When the highly luminescent green and red light emitting QDs were applied as color converters in InGaN blue LEDs, resulting cool white QD-LEDs showed 41lm/W and more than 100% of color reproducibility compared to NTSC standard in CIE1931 and maintained their optical properties for a long time operation. We also demonstrated a 46-inch LCD panel using the white QDLED backlight was successfully demonstrated (Figure).

Quantum‐Dot‐Sensitized Solar Cells

Abstract: Quantum-dot-sensitized solar cells (QDSCs) are a promising low-cost alternative to existing photovoltaic technologies such as crystalline silicon and thin inorganic films The absorption spectrum of quantum dots (QDs) can be tailored by controlling their size, and QDs can be produced by low-cost methods Nanostructures such as mesoporous films, nanorods, nanowires, nanotubes and nanosheets with high microscopic surface area, redox electrolytes and solid-state hole conductors are borrowed from standard dye-sensitized solar cells (DSCs) to fabricate electron conductor/QD monolayer/hole conductor junctions with high optical absorbance Herein we focus on recent developments in the field of mono- and polydisperse QDSCs Stability issues are adressed, coating methods are presented, performance is reviewed and special emphasis is given to the importance of energy-level alignment to increase the light to electric power conversion efficiency

Depleted-Heterojunction Colloidal Quantum Dot Solar Cells

Abstract: Colloidal quantum dot (CQD) photovoltaics combine low-cost solution processability with quantum size-effect tunability to match absorption with the solar spectrum. Rapid recent advances in CQD photovoltaics have led to impressive 3.6% AM1.5 solar power conversion efficiencies. Two distinct device architectures and operating mechanisms have been advanced. The first—the Schottky device—was optimized and explained in terms of a depletion region driving electron−hole pair separation on the semiconductor side of a junction between an opaque low-work-function metal and a p-type CQD film. The second—the excitonic device—employed a CQD layer atop a transparent conductive oxide (TCO) and was explained in terms of diffusive exciton transport via energy transfer followed by exciton separation at the type-II heterointerface between the CQD film and the TCO. Here we fabricate CQD photovoltaic devices on TCOs and show that our devices rely on the establishment of a depletion region for field-driven charge transport and...

Large, solution-processable graphene quantum dots as light absorbers for photovoltaics.

Abstract: Graphenes have very attractive properties for photovoltaics. Their tunable bandgap and large optical absorptivity are desirable for efficient light harvesting. Their electronic levels and interfacing with other materials for charge transfer processes can both be tuned with well-developed carbon chemistry. Graphenes have also been shown to have very large charge mobilities, which could be useful for charge collection in solar cells. In addition, they consist of elements abundant on Earth and are environmentally friendly. However, these important properties have not been taken advantage of because graphenes that are large enough to be useful for photovoltaics have extremely poor solubility and have a strong tendency to aggregate into graphite. Here we present a novel solubilization strategy for large graphene nanostructures. It has enabled us to synthesize solution-processable, black graphene quantum dots with uniform size through solution chemistry, and we show that they can be used as sensitizers for sola...

A diamond nanowire single-photon source

Abstract: The development of a robust light source that emits one photon at a time will allow new technologies such as secure communication through quantum cryptography. Devices based on fluorescent dye molecules, quantum dots and carbon nanotubes have been demonstrated, but none has combined a high single-photon flux with stable, room-temperature operation. Luminescent centres in diamond have recently emerged as a stable alternative, and, in the case of nitrogen-vacancy centres, offer spin quantum bits with optical readout. However, these luminescent centres in bulk diamond crystals have the disadvantage of low photon out-coupling. Here, we demonstrate a single-photon source composed of a nitrogen-vacancy centre in a diamond nanowire, which produces ten times greater flux than bulk diamond devices, while using ten times less power. This result enables a new class of devices for photonic and quantum information processing based on nanostructured diamond, and could have a broader impact in nanoelectromechanical systems, sensing and scanning probe microscopy.

Multiple Exciton Collection in a Sensitized Photovoltaic System

Abstract: Multiple exciton generation, the creation of two electron-hole pairs from one high-energy photon, is well established in bulk semiconductors, but assessments of the efficiency of this effect remain controversial in quantum-confined systems like semiconductor nanocrystals. We used a photoelectrochemical system composed of PbS nanocrystals chemically bound to TiO 2 single crystals to demonstrate the collection of photocurrents with quantum yields greater than one electron per photon. The strong electronic coupling and favorable energy level alignment between PbS nanocrystals and bulk TiO 2 facilitate extraction of multiple excitons more quickly than they recombine, as well as collection of hot electrons from higher quantum dot excited states. Our results have implications for increasing the efficiency of photovoltaic devices by avoiding losses resulting from the thermalization of photogenerated carriers.

Synthesis of large, stable colloidal graphene quantum dots with tunable size.

Abstract: We report a solution-chemistry-based approach to large, stable colloidal graphene quantum dots with uniform size and shape. The versatility of solution chemistry allows us to tune the structures of the graphenes and thus their properties.

Layered graphene/quantum dots for photovoltaic devices.

Abstract: To meet the increasing demand of clean energy the harvesting of electricity from solar incident photons with high efficiency at economically viable cost is needed. Quantum dot (QD) based solar cells are poised to play a leading role in this revolution owing to their potential in exceeding the Shockley–Queissar limit, their size-tuned optical response, and their efficient multiple carrier generation. 6] A major challenge in developing high-performance QD solar cells is the effective separation of photogenerated electron–hole pairs and the transfer of the electrons to the electrode. Strategies that have been tried include the introduction of nanomaterials with a suitable band energy as efficient acceptors. Carbon, an environmentally friendly and inexpensive material, exists in a variety of nanostructures ranging from insulator/semiconducting diamond to metallic/semimetallic graphite, conducting/semiconducting fullerenes, and single-walled carbon nanotubes (SWNTs), 10] and recently has been widely used in QD solar cells. Particularly, SWNTs 12] and stacked-cup carbon nanotubes have been used as efficient acceptors to enhance photoinduced charge transfer for improved performance because of their unique one-dimensional nanostructure and appropriate band energy. However, the efficiency of carbon nanomaterial based QD solar cells reported so far is still low (incident photon-to-charge-carrier conversion efficiency (IPCE) 5 % and photocurrent response 0.4 mAcm 2 under light illumination of 100 mWcm ), which is still some distance from the requirement for the next generation of solar cells. Graphene, a new class of two-dimensional carbon material with single-atom-thick layer features different from balllike C60 and one-dimensional carbon nanotubes, has attracted attention in recent years. As a result of its high specific surface area for a large interface, high mobility up to 10000 cm V 1 s , and tunable band gap, graphene should be a very promising electron acceptor in photovoltaic devices. In this work, a novel layered nanofilm of graphene/QDs was constructed from all aqueous solutions to fabricate a photovoltaic device using graphene as acceptor, demonstrating the best performance (IPCE of 16% and photoresponse of 1.08 mAcm 2 under light illumination of 100 mWcm ) in all reported carbon/QD solar cells. For a better understanding of the mechanism of the graphene in improving the performance of the device, the graphene/QDs and SWNT/QDs photovoltaic devices are compared. The fabrication of the layered graphene/QDs device is shown schematically in Figure 1. Chemically reduced graphene was used not only because of its unique properties

Quantum Criticality in an Ising Chain: Experimental Evidence for Emergent E8 Symmetry

Abstract: Quantum phase transitions take place between distinct phases of matter at zero temperature. Near the transition point, exotic quantum symmetries can emerge that govern the excitation spectrum of the system. A symmetry described by the E8 Lie group with a spectrum of eight particles was long predicted to appear near the critical point of an Ising chain. We realize this system experimentally by using strong transverse magnetic fields to tune the quasi-one-dimensional Ising ferromagnet CoNb2O6 (cobalt niobate) through its critical point. Spin excitations are observed to change character from pairs of kinks in the ordered phase to spin-flips in the paramagnetic phase. Just below the critical field, the spin dynamics shows a fine structure with two sharp modes at low energies, in a ratio that approaches the golden mean predicted for the first two meson particles of the E8 spectrum. Our results demonstrate the power of symmetry to describe complex quantum behaviors.

Modeling high-efficiency quantum dot sensitized solar cells

Abstract: With energy conversion efficiencies in continuous growth, quantum dot sensitized solar cells (QDSCs) are currently under an increasing interest, but there is an absence of a complete model for these devices. Here, we compile the latest developments in this kind of cells in order to attain high efficiency QDSCs, modeling the performance. CdSe QDs have been grown directly on a TiO(2) surface by successive ionic layer adsorption and reaction to ensure high QD loading. ZnS coating and previous growth of CdS were analyzed. Polysulfide electrolyte and Cu(2)S counterelectrodes were used to provide higher photocurrents and fill factors, FF. Incident photon-to-current efficiency peaks as high as 82%, under full 1 sun illumination, were obtained, which practically overcomes the photocurrent limitation commonly observed in QDSCs. High power conversion efficiency of up to 3.84% under full 1 sun illumination (V(oc) = 0.538 V, j(sc) = 13.9 mA/cm(2), FF = 0.51) and the characterization and modeling carried out indicate that recombination has to be overcome for further improvement of QDSC.

Spin–orbit qubit in a semiconductor nanowire

Abstract: Motion of electrons can influence their spins through a fundamental effect called spin–orbit interaction This interaction provides a way to control spins electrically and thus lies at the foundation of spintronics Even at the level of single electrons, the spin–orbit interaction has proven promising for coherent spin rotations Here we implement a spin–orbit quantum bit (qubit) in an indium arsenide nanowire, where the spin–orbit interaction is so strong that spin and motion can no longer be separated In this regime, we realize fast qubit rotations and universal single-qubit control using only electric fields; the qubits are hosted in single-electron quantum dots that are individually addressable We enhance coherence by dynamically decoupling the qubits from the environment Nanowires offer various advantages for quantum computing: they can serve as one-dimensional templates for scalable qubit registers, and it is possible to vary the material even during wire growth Such flexibility can be used to design wires with suppressed decoherence and to push semiconductor qubit fidelities towards error correction levels Furthermore, electrical dots can be integrated with optical dots in p–n junction nanowires The coherence times achieved here are sufficient for the conversion of an electronic qubit into a photon, which can serve as a flying qubit for long-distance quantum communication

Bandgap-like strong fluorescence in functionalized carbon nanoparticles.

Abstract: Semiconductor quantum dots (QDs), especially the highly fluorescent CdSe-based core-shell nanostructures, have generated much excitement for their variety of potential applications in optical bioimaging and beyond.[1,2] These QDs are widely considered as being more advantageous over conventional organic dyes as well as genetically engineered fluorescent proteins in terms of optical brightness and photostability.[1,3–5] However, a serious disadvantage with these popular QDs is their containing heavy metals such as cadmium, whose significant toxicity and environmental hazard are well-documented.[6–9] Alternative benign (nontoxic) QD-like fluorescent nanomaterials have therefore been pursued, including the recent finding of fluorescent carbon nanoparticles (dubbed “carbon dots”).[10,11]

Ultrabright source of entangled photon pairs

Abstract: Entangled photon pairs are essential components for practical quantum information applications. Two different approaches for producing entanglement are available: parametric conversion in a nonlinear optical medium, or radiative decay of electron–hole pairs trapped in a semiconductor quantum dot. The first approach has a low intrinsic efficiency; the second suffers from poor collection efficiency. In general, collection of emitted photons from quantum dots is often improved by coupling them to an optical cavity, but this is not straightforward to implement for entangled photon pairs. Dousse et al. have now constructed a suitable optical cavity in the form of a 'photonic molecule' — two connecting identical microcavities that are deterministically coupled to the optically active modes of a pre-selected quantum dot. They show that entangled photon pairs are emitted into two cavity modes, with a rate of 0.12 per excitation pulse. The authors believe that improvements in the fabrication of the device should enable triggered sources of entangled photon pairs, with an overall (creation and collection) efficiency of 80%. Quantum information science requires a source of entangled photon pairs, but existing sources suffer from a low intrinsic efficiency or poor extraction efficiency. Collecting emitted photons from quantum dots can be improved by coupling the dots to an optical cavity, but this is not easy for entangled photon pairs. Now, a suitable optical cavity has been made in the form of a 'photonic' molecule — two identical, connecting microcavities that are deterministically coupled to the optically active modes of a pre-selected quantum dot. A source of triggered entangled photon pairs is a key component in quantum information science1; it is needed to implement functions such as linear quantum computation2, entanglement swapping3 and quantum teleportation4. Generation of polarization entangled photon pairs can be obtained through parametric conversion in nonlinear optical media5,6,7 or by making use of the radiative decay of two electron–hole pairs trapped in a semiconductor quantum dot8,9,10,11. Today, these sources operate at a very low rate, below 0.01 photon pairs per excitation pulse, which strongly limits their applications. For systems based on parametric conversion, this low rate is intrinsically due to the Poissonian statistics of the source12. Conversely, a quantum dot can emit a single pair of entangled photons with a probability near unity but suffers from a naturally very low extraction efficiency. Here we show that this drawback can be overcome by coupling an optical cavity in the form of a ‘photonic molecule’13 to a single quantum dot. Two coupled identical pillars—the photonic molecule—were etched in a semiconductor planar microcavity, using an optical lithography method14 that ensures a deterministic coupling to the biexciton and exciton energy states of a pre-selected quantum dot. The Purcell effect ensures that most entangled photon pairs are emitted into two cavity modes, while improving the indistinguishability of the two optical recombination paths15,16. A polarization entangled photon pair rate of 0.12 per excitation pulse (with a concurrence of 0.34) is collected in the first lens. Our results open the way towards the fabrication of solid state triggered sources of entangled photon pairs, with an overall (creation and collection) efficiency of 80%.

Double-Sided CdS and CdSe Quantum Dot Co-Sensitized ZnO Nanowire Arrays for Photoelectrochemical Hydrogen Generation

Abstract: We report the design and characterization of a novel double-sided CdS and CdSe quantum dot cosensitized ZnO nanowire arrayed photoanode for photoelectrochemical (PEC) hydrogen generation. The double-sided design represents a simple analogue of tandem cell structure, in which the dense ZnO nanowire arrays were grown on an indium−tin oxide substrate followed by respective sensitization of CdS and CdSe quantum dots on each side. As-fabricated photoanode exhibited strong absorption in nearly the entire visible spectrum up to 650 nm, with a high incident-photon-to-current-conversion efficiency (IPCE) of ∼45% at 0 V vs Ag/AgCl. On the basis on a single white light illumination of 100 mW/cm2, the photoanode yielded a significant photocurrent density of ∼12 mA/cm2 at 0.4 V vs Ag/AgCl. The photocurrent and IPCE were enhanced compared to single quantum dot sensitized structures as a result of the band alignment of CdS and CdSe in electrolyte. Moreover, in comparison to single-sided cosensitized layered structures, ...

Near-infrared photoluminescent Ag2S quantum dots from a single source precursor.

Abstract: Monodisperse Ag(2)S quantum dots (QDs) were synthesized via pyrolysis of Ag(DDTC) in oleic acid, octadecylamine, and 1-octadecene. The uniform alkyl-capped Ag(2)S QDs with a size of 10.2 nm emit near-IR emission at 1058 nm under 785 nm excitation.

Superresolution Imaging using Single-Molecule Localization

Abstract: Superresolution imaging is a rapidly emerging new field of microscopy that dramatically improves the spatial resolution of light microscopy by over an order of magnitude (approximately 10-20-nm resolution), allowing biological processes to be described at the molecular scale. Here, we discuss a form of superresolution microscopy based on the controlled activation and sampling of sparse subsets of photoconvertible fluorescent molecules. In this single-molecule-based imaging approach, a wide variety of probes have proved valuable, ranging from genetically encodable photoactivatable fluorescent proteins to photoswitchable cyanine dyes. These have been used in diverse applications of superresolution imaging: from three-dimensional, multicolor molecule localization to tracking of nanometric structures and molecules in living cells. Single-molecule-based superresolution imaging thus offers exciting possibilities for obtaining molecular-scale information on biological events occurring at variable timescales.

Synergistic effect of CdSe quantum dot sensitization and nitrogen doping of TiO(2) nanostructures for photoelectrochemical solar hydrogen generation.

Abstract: We report the synthesis and photoelectrochemical (PEC) studies of TiO(2) nanoparticles and nanowires simultaneously doped with nitrogen and sensitized with CdSe quantum dots (QDs). These novel nanocomposite structures have been applied successfully as photoanodes for PEC hydrogen generation using Na(2)S and Na(2)SO(3) as sacrificial reagents. We observe significant enhanced photoresponse in these nanocomposites compared to N-doped TiO(2) or CdSe QD sensitized TiO(2). The enhancement is attributed to the synergistic effect of CdSe sensitization and N-doping that facilitate hole transfer/transport from CdSe to TiO(2) through oxygen vacancy states (V(o)) mediated by N-doping. The results demonstrate the importance of designing and manipulating the energy band alignment in composite nanomaterials for fundamentally improving charge separation and transport and thereby PEC properties.

Scalable templated growth of graphene nanoribbons on SiC

Abstract: In spite of its excellent electronic properties, the use of graphene in field-effect transistors is not practical at room temperature without modification of its intrinsically semimetallic nature to introduce a bandgap. Quantum confinement effects can create a bandgap in graphene nanoribbons, but existing nanoribbon fabrication methods are slow and often produce disordered edges that compromise electronic properties. Here, we demonstrate the self-organized growth of graphene nanoribbons on a templated silicon carbide substrate prepared using scalable photolithography and microelectronics processing. Direct nanoribbon growth avoids the need for damaging post-processing. Raman spectroscopy, high-resolution transmission electron microscopy and electrostatic force microscopy confirm that nanoribbons as narrow as 40 nm can be grown at specified positions on the substrate. Our prototype graphene devices exhibit quantum confinement at low temperatures (4 K), and an on-off ratio of 10 and carrier mobilities up to 2,700 cm(2) V(-1) s(-1) at room temperature. We demonstrate the scalability of this approach by fabricating 10,000 top-gated graphene transistors on a 0.24-cm(2) SiC chip, which is the largest density of graphene devices reported to date.

Colloidal PbS Quantum Dot Solar Cells with High Fill Factor

Abstract: We fabricate PbS colloidal quantum dot (QD)-based solar cells using a fullerene derivative as the electron-transporting layer (ETL). A thiol treatment and oxidation process are used to modify the morphology and electronic structure of the QD films, resulting in devices that exhibit a fill factor (FF) as high as 62%. We also show that, for QDs with a band gap of less than 1 eV, an open-circuit voltage (VOC) of 0.47 V can be achieved. The power conversion efficiency reaches 1.3% under 1 sun AM1.5 test conditions and 2.4% under monochromatic infrared (λ = 1310 nm) illumination. A consistent mechanism for device operation is developed through a circuit model and experimental measurements, shedding light on new approaches for optimization of solar cell performance by modifying the interface between the QDs and the neighboring charge transport layers.

In vivo quantum-dot toxicity assessment

Abstract: Quantum dots have potential in biomedical applications, but concerns persist about their safety. Most toxicology data is derived from in vitro studies and may not reflect in vivo responses. Here, an initial systematic animal toxicity study of CdSe-ZnS core-shell quantum dots in healthy Sprague-Dawley rats is presented. Biodistribution, animal survival, animal mass, hematology, clinical biochemistry, and organ histology are characterized at different concentrations (2.5-15.0 nmol) over short-term ( 80 days) periods. The results show that the quantum dot formulations do not cause appreciable toxicity even after their breakdown in vivo over time. To generalize the toxicity of quantum dots in vivo, further investigations are still required. Some of these investigations include the evaluation of quantum dot composition (e.g., PbS versus CdS), surface chemistry (e.g., functionalization with amines versus carboxylic acids), size (e.g., 2 versus 6 nm), and shape (e.g., spheres versus rods), as well as the effect of contaminants and their byproducts on biodistribution behavior and toxicity. Combining the results from all of these studies will eventually lead to a conclusion regarding the issue of quantum dot toxicity.

Colloidal quantum dot light-emitting devices

Abstract: Colloidal quantum dot light-emitting devices (QD-LEDs) have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI). We review the key advantages of using quantum dots (QDs) in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs - optical excitation, Fo¨ rster energy transfer, and direct charge injection - that have been leveraged to create QD-LEDs. We outline the challenges facing QDLED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desirable color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (>65 lumens per Watt). We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs. Keywords: nanocrystals; optoelectronics; displays; lighting (Published: 7 July 2010) Citation: Nano Reviews 2010, 1: 5202 - DOI: 10.3402/nano.v1i0.5202

Nanoscience and Nanostructures for Photovoltaics and Solar Fuels

Abstract: Quantum confinement of electronic particles (negative electrons and positive holes) in nanocrystals produces unique optical and electronic properties that have the potential to enhance the power conversion efficiency of solar cells for photovoltaic and solar fuels production at lower cost. These approaches and applications are labeled third generation solar photon conversion. Prominent among these unique properties is the efficient formation of more than one electron-hole pair (called excitons in nanocrystals) from a single absorbed photon. In isolated nanocrystals that have three-dimensional confinement of charge carriers (quantum dots) or two-dimensional confinement (quantum wires and rods) this process is termed multiple exciton generation. This Perspective presents a summary of our present understanding of the science of optoelectronic properties of nanocrystals and a prognosis for and review of the technological status of nanocrystals and nanostructures for third generation photovoltaic cells and solar fuels production.

Rapid and sensitive detection of protein biomarker using a portable fluorescence biosensor based on quantum dots and a lateral flow test strip.

Abstract: A portable fluorescence biosensor with rapid and ultrasensitive response for protein biomarker has been built up with quantum dots and a lateral flow test strip. The superior signal brightness and high photostability of quantum dots are combined with the promising advantages of a lateral flow test strip and result in high sensitivity and selectivity and speed for protein detection. Nitrated ceruloplasmin, a significant biomarker for cardiovascular disease, lung cancer, and stress response to smoking, was used as model protein biomarker to demonstrate the good performances of this proposed quantum dot-based lateral flow test strip. Quantitative detection of nitrated ceruloplasmin was realized by recording the fluorescence intensity of quantum dots captured on the test line. Under optimal conditions, this portable fluorescence biosensor displays rapid responses for nitrated ceruloplasmin with the concentration as low as 1 ng/mL. Furthermore, the biosensor was successfully utilized for spiked human plasma sa...