Showing papers on "Quantum dot published in 2019"
TL;DR: In this paper, multiple interlayer exciton resonances with either positive or negative circularly polarized emission were observed in a molybdenum diselenide/tungsten diselinide (MoSe2/WSe2) heterobilayer with a small twist angle.
Abstract: Recent advances in the isolation and stacking of monolayers of van der Waals materials have provided approaches for the preparation of quantum materials in the ultimate two-dimensional limit1,2. In van der Waals heterostructures formed by stacking two monolayer semiconductors, lattice mismatch or rotational misalignment introduces an in-plane moire superlattice3. It is widely recognized that the moire superlattice can modulate the electronic band structure of the material and lead to transport properties such as unconventional superconductivity4 and insulating behaviour driven by correlations5–7; however, the influence of the moire superlattice on optical properties has not been investigated experimentally. Here we report the observation of multiple interlayer exciton resonances with either positive or negative circularly polarized emission in a molybdenum diselenide/tungsten diselenide (MoSe2/WSe2) heterobilayer with a small twist angle. We attribute these resonances to excitonic ground and excited states confined within the moire potential. This interpretation is supported by recombination dynamics and by the dependence of these interlayer exciton resonances on twist angle and temperature. These results suggest the feasibility of engineering artificial excitonic crystals using van der Waals heterostructures for nanophotonics and quantum information applications. Multiple interlayer exciton resonances in a MoSe2/WSe2 heterobilayer with a small twist angle are attributed to excitonic ground and excited states confined within the moire potential.
973 citations
TL;DR: A method of engineering efficient and stable InP/ZnSe/ ZnS quantum dot light-emitting diodes (QD-LEDs) has improved their performance to the level of state-of-the-art cadmium-containing QD- LEDs, removing the problem of the toxicity of cadMium in large-panel displays.
Abstract: Quantum dot (QD) light-emitting diodes (LEDs) are ideal for large-panel displays because of their excellent efficiency, colour purity, reliability and cost-effective fabrication1-4. Intensive efforts have produced red-, green- and blue-emitting QD-LEDs with efficiencies of 20.5 per cent4, 21.0 per cent5 and 19.8 per cent6, respectively, but it is still desirable to improve the operating stability of the devices and to replace their toxic cadmium composition with a more environmentally benign alternative. The performance of indium phosphide (InP)-based materials and devices has remained far behind those of their Cd-containing counterparts. Here we present a synthetic method of preparing a uniform InP core and a highly symmetrical core/shell QD with a quantum yield of approximately 100 per cent. In particular, we add hydrofluoric acid to etch out the oxidative InP core surface during the growth of the initial ZnSe shell and then we enable high-temperature ZnSe growth at 340 degrees Celsius. The engineered shell thickness suppresses energy transfer and Auger recombination in order to maintain high luminescence efficiency, and the initial surface ligand is replaced with a shorter one for better charge injection. The optimized InP/ZnSe/ZnS QD-LEDs showed a theoretical maximum external quantum efficiency of 21.4 per cent, a maximum brightness of 100,000 candelas per square metre and an extremely long lifetime of a million hours at 100 candelas per square metre, representing a performance comparable to that of state-of-the-art Cd-containing QD-LEDs. These as-prepared InP-based QD-LEDs could soon be usable in commercial displays.
655 citations
TL;DR: The authors suggest that with the potential of these nanomaterials in sensing more research is needed on understanding their optical properties and why the synthetic methods influence their properties so much, into methods of surface functionalization that provide greater selectivity in sensing and into new sensing concepts that utilise the virtues of these nano-materials.
Abstract: Carbon and graphene quantum dots (CQDs and GQDs), known as zero-dimensional (0D) nanomaterials, have been attracting increasing attention in sensing and bioimaging. Their unique electronic, fluores...
570 citations
TL;DR: In this paper, a metal-free heterostructure photocatalyst constructed by boron nitride quantum dots (BNQDs) and ultrathin porous g-C3N4 (UPCN) was successfully developed for overcoming these defects.
Abstract: Graphitic carbon nitride (g-C3N4) has enormous potential for photocatalysis, but only possesses moderate activity because of excitonic effects and sluggish charge transfer. Herein, metal-free heterostructure photocatalyst constructed by boron nitride quantum dots (BNQDs) and ultrathin porous g-C3N4 (UPCN) was successfully developed for overcoming these defects. Results showed that the BNQDs loaded UPCN can simultaneously promote the dissociation of excitons and accelerate the transfer of charges owing to the negatively charged functional groups on the surface of BNQDs as well as the ultrathin and porous nanostructure of g-C3N4. Benefiting from the intensified exciton dissociation and charge transfer, the BNQDs/UPCN (BU) photocatalyst presented superior visible-light-driven molecular oxygen activation ability, such as superoxide radical ( O2−) generation and hydrogen peroxide (H2O2) production. The average O2− generation rate of the optimal sample (BU-3) was estimated to be 0.25 μmol L−1 min−1, which was about 2.3 and 1.6 times than that of bulk g-C3N4 and UPCN. Moreover, the H2O2 production by BU-3 was also higher than that of bulk g-C3N4 (22.77 μmol L−1) and UPCN (36.13 μmol L−1), and reached 72.30 μmol L−1 over 60 min. This work reveals how rational combination of g-C3N4 with BNQDs can endow it with improved photocatalytic activity for molecular oxygen activation, and provides a novel metal-free and highly efficient photocatalyst for environmental remediation and energy conversion.
512 citations
TL;DR: In this paper, the authors report red, green and blue quantum dot light-emitting diodes based on CdSe/ZnSe core/shell structures that combine efficient operation with high brightness.
Abstract: Quantum dot light-emitting diodes are promising light sources for applications in displays. However, to date, there have been no reports of devices that simultaneously offer both high brightness and high external quantum efficiency. Here, we report red, green and blue quantum dot light-emitting diodes based on CdSe/ZnSe core/shell structures that have these attributes. We demonstrate devices with maximum external quantum efficiencies of 21.6%, 22.9% and 8.05% for red, green and blue colours with corresponding brightness of 13,300 cd m–2, 52,500 cd m–2 and 10,100 cd m–2. The devices also offer peak luminance of 356,000 cd m–2, 614,000 cd m–2 and 62,600 cd m–2, respectively. We postulate that this high performance is due to the use of Se throughout the core/shell regions and the existence of alloyed bridging layers at the core/shell interfaces. This study suggests that in the future visible quantum dot light-emitting diodes will also be suitable for lighting applications. Red, green and blue CdSe/ZnSe quantum dot light-emitting diodes combine efficient operation with high brightness.
505 citations
TL;DR: As understanding of the degradation mechanisms of QDs increases and more stable QDs and display devices are developed, QDs are expected to play critical roles in advanced display applications.
Abstract: Quantum dots (QDs) are being highlighted in display applications for their excellent optical properties, including tunable bandgaps, narrow emission bandwidth, and high efficiency. However, issues with their stability must be overcome to achieve the next level of development. QDs are utilized in display applications for their photoluminescence (PL) and electroluminescence. The PL characteristics of QDs are applied to display or lighting applications in the form of color-conversion QD films, and the electroluminescence of QDs is utilized in quantum dot light-emitting diodes (QLEDs). Studies on the stability of QDs and QD devices in display applications are reviewed herein. QDs can be degraded by oxygen, water, thermal heating, and UV exposure. Various approaches have been developed to protect QDs from degradation by controlling the composition of their shells and ligands. Phosphorescent QDs have been protected by bulky ligands, physical incorporation in polymer matrices, and covalent bonding with polymer matrices. The stability of electroluminescent QLEDs can be enhanced by using inorganic charge transport layers and by improving charge balance. As understanding of the degradation mechanisms of QDs increases and more stable QDs and display devices are developed, QDs are expected to play critical roles in advanced display applications.
388 citations
TL;DR: The performance of photodetectors fabricated from emerging semiconductors such as perovskites, quantum dots, two-dimensional materials or organics can be prone to misinterpretation as discussed by the authors.
Abstract: The performance of photodetectors fabricated from emerging semiconductors such as perovskites, quantum dots, two-dimensional materials or organics, for example, can be prone to misinterpretation. This Comment exposes the problems and proposes some guidelines for accurate characterization.
381 citations
TL;DR: In this article, an entangled photon pair source with high brightness and indistinguishability was presented by deterministically embedding GaAs quantum dots in broadband photonic nanostructures that enable Purcell-enhanced emission.
Abstract: The generation of high-quality entangled photon pairs has been a long-sought goal in modern quantum communication and computation. So far, the most widely used entangled photon pairs have been generated from spontaneous parametric down-conversion (SPDC), a process that is intrinsically probabilistic and thus relegated to a regime of low rates of pair generation. In contrast, semiconductor quantum dots can generate triggered entangled photon pairs through a cascaded radiative decay process and do not suffer from any fundamental trade-off between source brightness and multi-pair generation. However, a source featuring simultaneously high photon extraction efficiency, high degree of entanglement fidelity and photon indistinguishability has been lacking. Here, we present an entangled photon pair source with high brightness and indistinguishability by deterministically embedding GaAs quantum dots in broadband photonic nanostructures that enable Purcell-enhanced emission. Our source produces entangled photon pairs with a pair collection probability of up to 0.65(4) (single-photon extraction efficiency of 0.85(3)), entanglement fidelity of 0.88(2), and indistinguishabilities of 0.901(3) and 0.903(3) (brackets indicate uncertainty on last digit). This immediately creates opportunities for advancing quantum photonic technologies.
331 citations
TL;DR: Boosting the Photocatalytic Ability of Cu2O Nanowires for CO2 Conversion by MXene Quantum Dots as discussed by the authors, was proposed to improve the performance of CO2 conversion.
Abstract: Boosting the Photocatalytic Ability of Cu2O Nanowires for CO2 Conversion by MXene Quantum Dots
309 citations
TL;DR: In this article, a polarization-orthogonal excitation collection scheme is designed to minimize the polarization filtering loss under resonant excitation, achieving a single-photon efficiency of 0.60.
Abstract: An optimal single-photon source should deterministically deliver one, and only one, photon at a time, with no trade-off between the source’s efficiency and the photon indistinguishability. However, all reported solid-state sources of indistinguishable single photons had to rely on polarization filtering, which reduced the efficiency by 50%, fundamentally limiting the scaling of photonic quantum technologies. Here, we overcome this long-standing challenge by coherently driving quantum dots deterministically coupled to polarization-selective Purcell microcavities. We present two examples: narrowband, elliptical micropillars and broadband, elliptical Bragg gratings. A polarization-orthogonal excitation–collection scheme is designed to minimize the polarization filtering loss under resonant excitation. We demonstrate a polarized single-photon efficiency of 0.60 ± 0.02 (0.56 ± 0.02), a single-photon purity of 0.975 ± 0.005 (0.991 ± 0.003) and an indistinguishability of 0.975 ± 0.006 (0.951 ± 0.005) for the micropillar (Bragg grating) device. Our work provides promising solutions for truly optimal single-photon sources combining near-unity indistinguishability and near-unity system efficiency simultaneously. Single-photon sources with a single-photon efficiency of 0.60, a single-photon purity of 0.975 and an indistinguishability of 0.975 are demonstrated. This is achieved by fabricating elliptical resonators around site-registered quantum dots.
309 citations
TL;DR: CQDs, their structure, and PL characteristics are introduced and recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.
TL;DR: Zhao et al. fabricate heterojunctions of colloidal perovskite quantum dots with different composition using layer-by-layer deposition and demonstrate improved photovoltaic performance with enhanced photocarrier harvesting.
Abstract: Metal halide perovskite semiconductors possess outstanding characteristics for optoelectronic applications including but not limited to photovoltaics. Low-dimensional and nanostructured motifs impart added functionality which can be exploited further. Moreover, wider cation composition tunability and tunable surface ligand properties of colloidal quantum dot (QD) perovskites now enable unprecedented device architectures which differ from thin-film perovskites fabricated from solvated molecular precursors. Here, using layer-by-layer deposition of perovskite QDs, we demonstrate solar cells with abrupt compositional changes throughout the perovskite film. We utilize this ability to abruptly control composition to create an internal heterojunction that facilitates charge separation at the internal interface leading to improved photocarrier harvesting. We show how the photovoltaic performance depends upon the heterojunction position, as well as the composition of each component, and we describe an architecture that greatly improves the performance of perovskite QD photovoltaics.
TL;DR: This is the first report of high and versatile stabilities of Pe-QD, which should enable their improved application in lighting, displays, and biologic imaging.
Abstract: The stability and optoelectronic device performance of perovskite quantum dots (Pe-QDs) are severely limited by present ligand strategies since these ligands exhibit a highly dynamic binding state, resulting in serious complications in QD purification and storage. Here, a "Br-equivalent" ligand strategy is developed in which the proposed strong ionic sulfonate heads, for example, benzenesulfonic acid, can firmly bind to the exposed Pb ions to form a steady binding state, and can also effectively eliminate the exciton trapping probability due to bromide vacancies. From these two aspects, the sulfonate heads play a similar role as natural Br ions in a perfect perovskite lattice. Using this approach, high photoluminescence quantum yield (PL QY) > 90% is facilely achieved without the need for amine-related ligands. Furthermore, the prepared PL QYs are well maintained after eight purification cycles, more than five months of storage, and high-flux photo-irradiation. This is the first report of high and versatile stabilities of Pe-QD, which should enable their improved application in lighting, displays, and biologic imaging.
TL;DR: Stochichiometry control within both core and shell regions of InP/ZnSe/ZNS core/shell/shell quantum dots (QDs) are introduced to advance their properties drastically, approaching those of state-of-the-art CdSe-based QDs.
Abstract: We introduce stoichiometry control within both core and shell regions of InP/ZnSe/ZnS core/shell/shell quantum dots (QDs) to advance their properties drastically, approaching those of state-of-the-art CdSe-based QDs. The resulting QDs possess near-unity photoluminescence quantum yield, monoexponential decay dynamics, narrow line width, and nonblinking at a single-dot level. Quantum-dot light-emitting diodes (QLEDs) with the InP/ZnSe/ZnS core/shell/shell QDs as emitters exhibit a peak external quantum efficiency of 12.2% and a maximum brightness of >10 000 cd m–2, greatly exceeding those of the Cd/Pb-free QLEDs reported in literature. These results pave the way toward Cd/Pb-free QDs as outstanding optical and optoelectronic materials.
TL;DR: In this article, a two-terminal colloidal quantum dot (CQD) dual-band detector is presented, which provides a bias-switchable spectral response in two distinct bands.
Abstract: Infrared multispectral imaging is attracting great interest with the increasing demand for sensitive, low-cost and scalable devices that can distinguish coincident spectral information. However, the widespread use of such detectors is still limited by the high cost of epitaxial semiconductors. In contrast, the solution processability and wide spectral tunability of colloidal quantum dots (CQDs) have inspired various inexpensive, high-performance optoelectronic devices. Here, we demonstrate a two-terminal CQD dual-band detector, which provides a bias-switchable spectral response in two distinct bands. A vertical stack of two rectifying junctions in a back-to-back diode configuration is created by engineering a strong and spatially stable doping process. By controlling the bias polarity and magnitude, the detector can be rapidly switched between short-wave infrared and mid-wave infrared at modulation frequencies up to 100 kHz with D* above 1010 jones at cryogenic temperature. The detector performance is illustrated by dual-band infrared imaging and remote temperature monitoring. Colloidal quantum dot detectors, switchable between short-wave infrared and mid-wave infrared, are demonstrated.
TL;DR: This work generates entangled photon pairs with a state fidelity of 0.90(1), pair generation rate, pair extraction efficiency, and photon indistinguishability simultaneously, and will open up many applications in high-efficiency multiphoton experiments and solid-state quantum repeaters.
Abstract: An outstanding goal in quantum optics and scalable photonic quantum technology is to develop a source that each time emits one and only one entangled photon pair with simultaneously high entanglement fidelity, extraction efficiency, and photon indistinguishability. By coherent two-photon excitation of a single InGaAs quantum dot coupled to a circular Bragg grating bull's-eye cavity with a broadband high Purcell factor of up to 11.3, we generate entangled photon pairs with a state fidelity of 0.90(1), pair generation rate of 0.59(1), pair extraction efficiency of 0.62(6), and photon indistinguishability of 0.90(1) simultaneously. Our work will open up many applications in high-efficiency multiphoton experiments and solid-state quantum repeaters.
TL;DR: A detailed discussion of the biodistribution and toxicity of quantum dots, and recent advances to improve long-term stability in biological buffers, increase quantum yield following bioconjugation, and improve clearance from the body are presented.
TL;DR: Doping divalent Cu2+ ions into the perovskite lattice is addressed, resulting in the improvement of both the thermal stability and the optical performance of CsPb1- xCu x(Br/Cl)3 QDs, which exhibit bright blue photoluminescence at 450-460 nm, with a high quantum yield of over 80%.
Abstract: All-inorganic perovskite quantum dots (QDs) have emerged as potentially promising materials for lighting and displays, but their poor thermal stability restricts their practical application. In addition, optical characteristics of the blue-emitting CsPbX3 QDs lag behind their red- and green-emitting counterparts. Herein, we addressed these two issues by doping divalent Cu2+ ions into the perovskite lattice to form CsPb1–xCuxX3 QDs. Extended X-ray absorption fine structure (EXAFS) measurements reveal that doping smaller Cu2+ guest ions induces a lattice contraction and eliminates halide vacancies, which leads to an increased lattice formation energy and improved short-range order of the doped perovskite QDs. This results in the improvement of both the thermal stability and the optical performance of CsPb1–xCux(Br/Cl)3 QDs, which exhibit bright blue photoluminescence at 450–460 nm, with a high quantum yield of over 80%. The CsPb1–xCuxX3 QD films maintain stable luminescence performance even when annealed at...
TL;DR: Ti3C2 MXene quantum dots (QDs) possess the activity of Pt as co-catalyst in promotion the photocatalytic H2 evolution to form heterostructure with g-C3N4 nanosheets (NSs) (denoted as g-N4@Ti2C2 QDs), causing the improvement of carrier transfer efficiency.
Abstract: The big challenging issues in photocatalytic H2 evolution are efficient separation of the photoinduced carriers, the stability of the catalyst, enhancing quantum efficiency, and requiring photoinduced electrons to enrich on photocatalysts' surface. Herein, Ti3C2 MXene quantum dots (QDs) possess the activity of Pt as a co-catalyst in promoting the photocatalytic H2 evolution to form heterostructures with g-C3N4 nanosheets (NSs) (denoted g-C3N4@Ti3C2 QDs). The photocatalytic H2 evolution rate of g-C3N4@Ti3C2 QD composites with an optimized Ti3C2 QD loading amounts (100 mL) is nearly 26, 3 and 10 times higher than pristine g-C3N4 NSs, Pt/g-C3N4, and Ti3C2 MXene sheet/g-C3N4, respectively. The Ti3C2 QDs increase the specific surface area of g-C3N4 and boost the density of the active site. Besides, metallic Ti3C2 QDs possess excellent electronic conductivity, causing the improvement of carrier transfer efficiency.
TL;DR: The results suggest that the perovskite QDs are ideal candidates for the detection of soft X-rays and for large-area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.
Abstract: Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed simple and low-cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft-X-ray-induced photocurrent is demonstrated in both rigid and flexible detectors based on all-inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft-X-ray beamline, high sensitivities of up to 1450 µC Gyair-1 cm-2 are achieved under an X-ray dose rate of 0.0172 mGyair s-1 with only 0.1 V bias voltage, which is about 70-fold more sensitive than conventional α-Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large-scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X-rays and for large-area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.
TL;DR: In this article, the authors demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single-photon emission with optical coherence times as long as 80 picoseconds, an appreciable fraction of their 210picosecond radiative lifetimes.
Abstract: Chemically made colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. We now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single-photon emission with optical coherence times as long as 80 picoseconds, an appreciable fraction of their 210-picosecond radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs. Our results present a starting point for the rational design of lead halide perovskite–based quantum emitters that have fast emission, wide spectral tunability, and scalable production and that benefit from the hybrid integration with nanophotonic components that has been demonstrated for colloidal materials.
TL;DR: In this article, the authors demonstrate a facile strategy that combines high power conversion efficiency (PCE) with high stability in CH3NH3PbI3 (MAPbI) solar cells, which utilizes inorganic perovskite quantum dots (QDs) to distribute elemental dopants uniformly across the MAPbI-3 film and attach ligands to the film surface.
TL;DR: In this paper, a review of the development of organic LEDs, inorganic LEDs, and QLEDs is presented, and the challenges of QDs for high-efficiency LEDs are discussed.
TL;DR: It is demonstrated that the incorporation of strontium ions can significantly increase the formation energies of α-CsPbI3 QDs and hence reduce the structure distortion to stabilize the cubic phase at the few-nanometer size.
Abstract: Cubic phase CsPbI3 quantum dots (α-CsPbI3 QDs) as a newly emerging type of semiconducting QDs hold tremendous promise for fundamental research and optoelectronic device applications. However, stable and sub-5 nm-sized α-CsPbI3 QDs have rarely been demonstrated so far due to their highly labile ionic structure and low phase stability. Here, we report a novel strontium-substitution along with iodide passivation strategy to stabilize the cubic phase of CsPbI3, achieving the facile synthesis of α-CsPbI3 QDs with a series of controllable sizes down to sub-5 nm. We demonstrate that the incorporation of strontium ions can significantly increase the formation energies of α-CsPbI3 QDs and hence reduce the structure distortion to stabilize the cubic phase at the few-nanometer size. The size ranging from 15 down to sub-5 nm of as-prepared stable α-CsPbI3 QDs allowed us to investigate their unique size-dependent optical properties. Strikingly, the few-nanometer-sized α-CsPbI3 QDs turned out to retain high photolumine...
TL;DR: In this article, a composite strategy to enhance the stability of water-sensitive CsPbBr3 quantum dots by embedding the QDs into the super-hydrophobic porous organic polymer frameworks (CPB@S...
Abstract: We present a novel composite strategy to enhance the stability of water-sensitive CsPbBr3 quantum dots (QDs) by embedding the QDs into the super-hydrophobic porous organic polymer frameworks (CPB@S...
TL;DR: The science behind quantum dots, various biomedical applications and their interaction with liver and kidney are reviewed and strategies towards modification of quantum dots for reducing cytotoxicity are illustrated and a glance at the future direction of Quantum dots is concluded.