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1.
Nano Lett ; 2020 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-32348146

RESUMO

Because of the toxicity of lead, searching for a lead-free halide perovskite semiconducting material with comparable optical and electronic properties is of great interest. Rare-earth-based halide perovskite represents a promising class of materials for this purpose. In this work, we demonstrate the solution-phase synthesis of single-crystalline CsEuCl3 nanocrystals with a uniform size distribution centered around 15 nm. The CsEuCl3 nanocrystals have photoluminescence emission centered at 435 nm, with a full width at half-maximum of 19 nm. Furthermore, CsEuCl3 nanocrystals can be embedded in a polymer matrix that provides enhanced stability under continuous laser irradiation. Lead-free rare-earth cesium europium halide perovskite nanocrystals represent a promising candidate to replace lead halide perovskites.

2.
Sci Adv ; 6(4): eaay4045, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32042900

RESUMO

Achieving perovskite-based high-color purity blue-emitting light-emitting diodes (LEDs) is still challenging. Here, we report successful synthesis of a series of blue-emissive two-dimensional Ruddlesden-Popper phase single crystals and their high-color purity blue-emitting LED demonstrations. Although this approach successfully achieves a series of bandgap emissions based on the different layer thicknesses, it still suffers from a conventional temperature-induced device degradation mechanism during high-voltage operations. To understand the underlying mechanism, we further elucidate temperature-induced device degradation by investigating the crystal structural and spectral evolution dynamics via in situ temperature-dependent single-crystal x-ray diffraction, photoluminescence (PL) characterization, and density functional theory calculation. The PL peak becomes asymmetrically broadened with a marked intensity decay, as temperature increases owing to [PbBr6]4- octahedra tilting and the organic chain disordering, which results in bandgap decrease. This study indicates that careful heat management under LED operation is a key factor to maintain the sharp and intense emission.

3.
Proc Natl Acad Sci U S A ; 116(47): 23404-23409, 2019 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-31685626

RESUMO

Phase transitions in halide perovskites triggered by external stimuli generate significantly different material properties, providing a great opportunity for broad applications. Here, we demonstrate an In-based, charge-ordered (In+/In3+) inorganic halide perovskite with the composition of Cs2In(I)In(III)Cl6 in which a pressure-driven semiconductor-to-metal phase transition exists. The single crystals, synthesized via a solid-state reaction method, crystallize in a distorted perovskite structure with space group I4/m with a = 17.2604(12) Å, c = 11.0113(16) Å if both the strong reflections and superstructures are considered. The supercell was further confirmed by rotation electron diffraction measurement. The pressure-induced semiconductor-to-metal phase transition was demonstrated by high-pressure Raman and absorbance spectroscopies and was consistent with theoretical modeling. This type of charge-ordered inorganic halide perovskite with a pressure-induced semiconductor-to-metal phase transition may inspire a range of potential applications.

4.
Nanoscale ; 11(41): 19586-19594, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31633140

RESUMO

Designing an efficient and stable hole transport layer (HTL) material is one of the essential ways to improve the performance of organic-inorganic perovskite solar cells (PSCs). Herein, for the first time, an efficient model of a hole transport material (HTM) is demonstrated by optimized doping of a conjugated polymer TFB (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine)]) with a non-hygroscopic p-type dopant F4-TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) for high-efficiency PSCs. The PSC with the F4-TCNQ doped TFB exhibits the best power conversion efficiency (PCE) of 17.46%, which surpasses that of the reference devices, i.e., 16.64 (LiTFSI + TBP-doped Spiro-OMeTAD as the HTM) and 11.01% (LiTFSI + TBP-doped TFB as the HTM). F4-TCNQ doped TFB was believed to favor efficient charge and energy transfer between the perovskite and the hole transport layer and to reduce charge recombination as evidenced by steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) analysis. Moreover, the hydrophobic nature of F4-TCNQ contributed to enhancing the stability of the device under ambient conditions with a RH of 45%. The device reported herein retained ca. 80% of its initial efficiency after 10 days, significantly superior to both LiTFSI + TBP-doped Spiro-OMeTAD (ca. 30%) and LiTFSI + TBP-doped TFB (ca. 10%) based counterparts. This simple yet novel strategy paves the way for demonstrating a promising route for a wide range of highly efficient solar cells and other photovoltaic applications.

5.
Biomed Pharmacother ; 118: 109268, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31545239

RESUMO

Danshen (salvia miltiorrhiza) and honghua(Carthamus tinctorius) were traditional herb pair with promoting blood circulation and removing blood stasis actions, in China. Both were widely used to treat cardiovascular diseases (CVD) for hundreds years, especially shown definite advantage in the treatment of ischemic heart disease (IHD). However, the mechanism of danshen-honghua herb pair (DHHP) in the treatment of IHD was still unclear. This study was focused on examining the effects and possible mechanisms of DHHP in rats with acute myocardial ischemia induced by isoproterenol (ISO). The results suggested that DHHP significantly ameliorated the myocardial tissue abnormalities, notablely inhibited the elevation of lactate dehydrogenase (LDH), creatine kinase (CK), aspartate aminotransferase (AST), creatinekinase isoenzyme (CK-MB) and cardiac troponin T (CTn-T) in plasma, obviously decreased the plasma levels of Tumor Necrosis Factor α (TNF-α), outstandingly inhibited the reduction of superoxide dismutase (SOD), catalase (CAT) caused by ISO, significantly inhibited the high expression of Bcl-2 assaciated X protein (Bax) and nuclear transcriptionfactor-κBP65 (NF-κBP65) protein, significantly induced the low expression of B-cell lymphoma-2 (Bcl-2) protein in acute myocardial ischemia rats. DHHP can obviously ameliorate hemodynamic parameters. In summary, DHHP can significantly improve myocardial ischemia in acute myocardial ischemia model rats caused by ISO. Anti-free radicals, anti-peroxidation, inhibition of cell apoptosis and anti- inflammation maybe are the potential mechanisms of DHHP anti-myocardial ischemia in acute myocardial ischemia rats in duced by ISO.


Assuntos
Medicamentos de Ervas Chinesas/uso terapêutico , Isquemia Miocárdica/tratamento farmacológico , Animais , Apoptose/efeitos dos fármacos , Aspartato Aminotransferases/sangue , Carthamus tinctorius , Creatina Quinase Forma MB/sangue , Hemorreologia/efeitos dos fármacos , Interleucina-6/metabolismo , Isoproterenol , L-Lactato Desidrogenase/sangue , Masculino , Isquemia Miocárdica/sangue , Isquemia Miocárdica/enzimologia , Isquemia Miocárdica/patologia , Miocárdio/patologia , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/patologia , Ratos Sprague-Dawley , Superóxido Dismutase/metabolismo , Fator de Transcrição RelA/metabolismo , Troponina T/sangue , Fator de Necrose Tumoral alfa/metabolismo , Proteína X Associada a bcl-2/metabolismo
6.
Chem Rev ; 119(15): 9153-9169, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31282661

RESUMO

All-photonic integrated circuits are promising platforms for future systems beyond the limitation of Moore's law. Over the last several decades, one-dimensional (1D) nanowires have demonstrated great potential in photonic circuitry because of their unique 1D structure to effectively generate and tightly confine optical signals as well as easily tunable optical properties. In this Review, we categorize nanowires based on the optical properties (i.e., semiconducting, metallic, and dielectric nanowires) for their potential photonic applications (as light emitters or plasmonic and photonic waveguides). We further discuss the recent efforts in integration of nanowire-based photonic elements toward next-generation optical information processors. However, there are still several challenges remaining before the nanowires are fully utilized as photonic building blocks. The scientific and technical challenges and outlooks are provided to indicate the future directions.

7.
Proc Natl Acad Sci U S A ; 116(26): 12648-12653, 2019 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-31189607

RESUMO

Ion exchange, as a postsynthetic transformation strategy, offers more flexibilities in controlling material compositions and structures beyond direct synthetic methodology. Observation of such transformation kinetics on the single-particle level with rich spatial and spectroscopic information has never been achieved. We report the quantitative imaging of anion exchange kinetics in individual single-crystalline halide perovskite nanoplates using confocal photoluminescence microscopy. We have systematically observed a symmetrical anion exchange pathway on the nanoplates with dependence on reaction time and plate thickness, which is governed by the crystal structure and the diffusion-limited transformation mechanism. Based on a reaction-diffusion model, the halide diffusion coefficient was estimated to be on the order of [Formula: see text] This diffusion-controlled mechanism leads to the formation of 2D perovskite heterostructures with spatially resolved coherent interface through the precisely controlled anion exchange reaction, offering a design protocol for tailoring functionalities of semiconductors at the nano-/microscale.

8.
J Am Chem Soc ; 141(20): 8296-8305, 2019 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-31055917

RESUMO

Metal halide perovskites exhibit outstanding optoelectronic properties: superior charge carrier mobilities, low densities of deep trap states, high photoluminescence quantum yield, and wide color tunability. The introduction of dopant ions provides pathways to manipulate the electronic and chemical features of perovskites. In metal halide perovskites ABX3, where A is a monovalent cation (e.g., methylammonium (MA+), Cs+), B is the divalent metal ion(s) (e.g., Pb2+, Sn2+), and X is the halide group (e.g., Cl-, Br-, or I-), the isovalent exchange of A- and X-site ions has been widely accomplished; in contrast, strategies to exchange B-site cations are underexamined. The activation energies for vacancy-mediated diffusion of B-site cations are much higher than those for A- and X-sites, leading to slow doping processes and low doping ratios. Herein we demonstrate a new method that exchanges B-site cations in perovskites. We design a series of metal carboxylate solutions that anchor on the perovskite surface, allowing fast and efficient doping of B-sites with both homovalent and heterovalent cations (e.g., Sn2+, Zn2+, Bi3+) at room temperature. The doping process in the reduced-dimensional perovskites is complete within 1 min, whereas a similar reaction only leads to the surface attachment of dopant ions in three-dimensional structures. We offer a model based on ammonium extraction and surface ion-pair substitution.

9.
Chem Rev ; 2019 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-31021609

RESUMO

Next-generation displays and lighting technologies require efficient optical sources that combine brightness, color purity, stability, substrate flexibility. Metal halide perovskites have potential use in a wide range of applications, for they possess excellent charge transport, bandgap tunability and, in the most promising recent optical source materials, intense and efficient luminescence. This review links metal halide perovskites' performance as efficient light emitters with their underlying materials electronic and photophysical attributes.

10.
J Phys Chem Lett ; 10(3): 419-426, 2019 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-30630317

RESUMO

Solution-processed perovskite quantum wells have been used to fabricate increasingly efficient and stable optoelectronic devices. Little is known about the dynamics of photogenerated excitons in perovskite quantum wells within the first few hundred femtoseconds-a crucial time scale on which energy and charge transfer processes may compete. Here we use ultrafast transient absorption and two-dimensional electronic spectroscopy to clarify the movement of excitons and charges in reduced-dimensional perovskite solids. We report excitonic funneling from strongly to weakly confined perovskite quantum wells within 150 fs, facilitated by strong spectral overlap and orientational alignment among neighboring wells. This energy transfer happens on time scales orders of magnitude faster than charge transfer, which we find to occur instead over 10s to 100s of picoseconds. Simulations of both Förster-type interwell exciton transfer and free carrier charge transfer are in agreement with these experimental findings, with theoretical exciton transfer calculated to occur in 100s of femtoseconds.

11.
Nature ; 562(7726): 245-248, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30305741

RESUMO

Metal halide perovskite materials are an emerging class of solution-processable semiconductors with considerable potential for use in optoelectronic devices1-3. For example, light-emitting diodes (LEDs) based on these materials could see application in flat-panel displays and solid-state lighting, owing to their potential to be made at low cost via facile solution processing, and could provide tunable colours and narrow emission line widths at high photoluminescence quantum yields4-8. However, the highest reported external quantum efficiencies of green- and red-light-emitting perovskite LEDs are around 14 per cent7,9 and 12 per cent8, respectively-still well behind the performance of organic LEDs10-12 and inorganic quantum dot LEDs13. Here we describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20 per cent. This achievement stems from a new strategy for managing the compositional distribution in the device-an approach that simultaneously provides high luminescence and balanced charge injection. Specifically, we mixed a presynthesized CsPbBr3 perovskite with a MABr additive (where MA is CH3NH3), the differing solubilities of which yield sequential crystallization into a CsPbBr3/MABr quasi-core/shell structure. The MABr shell passivates the nonradiative defects that would otherwise be present in CsPbBr3 crystals, boosting the photoluminescence quantum efficiency, while the MABr capping layer enables balanced charge injection. The resulting 20.3 per cent external quantum efficiency represents a substantial step towards the practical application of perovskite LEDs in lighting and display.

12.
Nat Commun ; 9(1): 3541, 2018 08 30.
Artigo em Inglês | MEDLINE | ID: mdl-30166537

RESUMO

Perovskite light-emitting diodes (PeLEDs) have shown excellent performance in the green and near-infrared spectral regions, with high color purity, efficiency, and brightness. In order to shift the emission wavelength to the blue, compositional engineering (anion mixing) and quantum-confinement engineering (reduced-dimensionality) have been employed. Unfortunately, LED emission profiles shift with increasing driving voltages due to either phase separation or the coexistence of multiple crystal domains. Here we report color-stable sky-blue PeLEDs achieved by enhancing the phase monodispersity of quasi-2D perovskite thin films. We selected cation combinations that modulate the crystallization and layer thickness distribution of the domains. The perovskite films show a record photoluminescence quantum yield of 88% at 477 nm. The corresponding PeLEDs exhibit stable sky-blue emission under high operation voltages. A maximum luminance of 2480 cd m-2 at 490 nm is achieved, fully one order of magnitude higher than the previous record for quasi-2D blue PeLEDs.

13.
Adv Mater ; 30(45): e1801996, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30160805

RESUMO

Next-generation displays require efficient light sources that combine high brightness, color purity, stability, compatibility with flexible substrates, and transparency. Metal halide perovskites are a promising platform for these applications, especially in light of their excellent charge transport and bandgap tunability. Low-dimensional perovskites, which possess perovskite domains spatially confined at the nanoscale, have further extended the degree of tunability and functionality of this materials platform. Herein, the advances in perovskite materials for light-emission applications are reviewed. Connections among materials properties, photophysical and electrooptic spectroscopic properties, and device performance are established. It is discussed how incompletely solved problems in these materials can be tackled, including the need for increased stability, efficient blue emission, and efficient infrared emission. In conclusion, an outlook on the technologies that can be realized using this material platform is presented.

14.
Pathol Res Pract ; 214(9): 1388-1394, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30098829

RESUMO

BACKGROUND: Though the levels of diagnosis and treatment of multiple myeloma (MM) have been largely improved recent years, the prognosis of these patients remain unacceptable. It is urgent for us to discover the exact mechanism and determine some new indicators for MM. MiRNAs play a critical role in the occurrence and progression of cancers, including MM. MiR-26b-5p has been reported to be closely related to cells proliferation in human pulmonary cancer, hepatocellular carcinoma and so on. MATERIAL AND METHODS: Here, we measured the expression of miR-26b-5p in MM samples and cell lines by real-time PCR. Then, Kaplan-Meier Curves were applied to assess the effect of miR-26b-5p expression on MM patients prognosis. Functionally, MTT assay and Flow cytometry were conducted to explore the functions of miR-26b-5p in cells proliferation and apoptosis. Furthermore, bioinformatics tools, Pearson's correlation coefficient analysis, gain-and loss of-function experiments and rescue experiment were used to determine the relationship between JAG1 and miR-26b-5p in MM cells. In addition, we also confirmed the role of JAG1 in MM cells proliferation and apoptosis by gain-and loss of-function experiments. RESULTS: Here, we reported for the first time that miR-26b-5p was under-expressed in MM by real-time PCR. Clinically, Kaplan-Meier Curves showed that MM patients with lower miR-26b-5p expression had worse prognosis. Functionally, MTT assay revealed that miR-26b-5p inhibited cells proliferation. Flow cytometry indicated that miR-26b-5p accelerated tumor cells apoptosis. Furthermore, bioinformatics tools, Pearson's correlation coefficient analysis gain-and loss of-function experiments showed that JAG1 was the target of miR-26b-5p in MM cells. And, gain-and loss of-function experiments for JAG1 confirmed that JAG1 was an oncogene in MM cells. What's more, rescue experiment showed that JAG1 mediated the function of miR-26b-5p in MM cells. CONCLUSION: MiR-26b-5p acts as a tumor suppressor through suppressing cells proliferation and inducing cells apoptosis via directly targeting JAG1 in MM. MiR-26b-5p could be a potential and ponderable tumor target for MM in future.


Assuntos
Regulação Neoplásica da Expressão Gênica/genética , Proteína Jagged-1/biossíntese , MicroRNAs/metabolismo , Mieloma Múltiplo/patologia , Apoptose/genética , Proliferação de Células/genética , Genes Supressores de Tumor , Humanos , Proteína Jagged-1/genética , Estimativa de Kaplan-Meier , MicroRNAs/genética , Mieloma Múltiplo/genética , Mieloma Múltiplo/mortalidade , Prognóstico
15.
Adv Mater ; 30(38): e1802858, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30091157

RESUMO

Electrochemical reduction of CO2 is a compelling route to store renewable electricity in the form of carbon-based fuels. Efficient electrochemical reduction of CO2 requires catalysts that combine high activity, high selectivity, and low overpotential. Extensive surface reconstruction of metal catalysts under high productivity operating conditions (high current densities, reducing potentials, and variable pH) renders the realization of tailored catalysts that maximize the exposure of the most favorable facets, the number of active sites, and the oxidation state all the more challenging. Earth-abundant transition metals such as tin, bismuth, and lead have been proven stable and product-specific, but exhibit limited partial current densities. Here, a strategy that employs bismuth oxyhalides as a template from which 2D bismuth-based catalysts are derived is reported. The BiOBr-templated catalyst exhibits a preferential exposure of highly active Bi ( 11¯0 ) facets. Thereby, the CO2 reduction reaction selectivity is increased to over 90% Faradaic efficiency and simultaneously stable current densities of up to 200 mA cm-2 are achieved-more than a twofold increase in the production of the energy-storage liquid formic acid compared to previous best Bi catalysts.

16.
Nat Commun ; 9(1): 1607, 2018 04 23.
Artigo em Inglês | MEDLINE | ID: mdl-29686304

RESUMO

Formamidinium-lead-iodide (FAPbI3)-based perovskites with bandgap below 1.55 eV are of interest for photovoltaics in view of their close-to-ideal bandgap. Record-performance FAPbI3-based solar cells have relied on fabrication via the sequential-deposition method; however, these devices exhibit unstable output under illumination due to the difficulty of incorporating cesium cations (stabilizer) in sequentially deposited films. Here we devise a perovskite seeding method that efficiently incorporates cesium and beneficially modulates perovskite crystallization. First, perovskite seed crystals are embedded in the PbI2 film. The perovskite seeds serve as cesium sources and act as nuclei to facilitate crystallization during the formation of perovskite. Perovskite films with perovskite seeding growth exhibit a lowered trap density, and the resulting planar solar cells achieve stabilized efficiency of 21.5% with a high open-circuit voltage of 1.13 V and a fill factor that exceeds 80%. The Cs-containing FAPbI3-based devices show a striking improvement in operational stability and retain 60% of their initial efficiency after 140 h operation under one sun illumination.

17.
Adv Mater ; 30(13): e1706275, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29441615

RESUMO

Wide-bandgap (WBG) formamidinium-cesium (FA-Cs) lead iodide-bromide mixed perovskites are promising materials for front cells well-matched with crystalline silicon to form tandem solar cells. They offer avenues to augment the performance of widely deployed commercial solar cells. However, phase instability, high open-circuit voltage (Voc ) deficit, and large hysteresis limit this otherwise promising technology. Here, by controlling the crystallization of FA-Cs WBG perovskite with the aid of a formamide cosolvent, light-induced phase segregation and hysteresis in perovskite solar cells are suppressed. The highly polar solvent additive formamide induces direct formation of the black perovskite phase, bypassing the yellow phases, thereby reducing the density of defects in films. As a result, the optimized WBG perovskite solar cells (PSCs) (Eg ≈ 1.75 eV) exhibit a high Voc of 1.23 V, reduced hysteresis, and a power conversion efficiency (PCE) of 17.8%. A PCE of 15.2% on 1.1 cm2 solar cells, the highest among the reported efficiencies for large-area PSCs having this bandgap is also demonstrated. These perovskites show excellent phase stability and thermal stability, as well as long-term air stability. They maintain ≈95% of their initial PCE after 1300 h of storage in dry air without encapsulation.

18.
J Phys Chem Lett ; 8(16): 3895-3901, 2017 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-28767258

RESUMO

Quasi-two-dimensional lead halide perovskites, MAn-1PbnX3n+1, are quantum confined materials with an ever-developing range of optoelectronic device applications. Like other semiconductors, the correlated motion of electrons and holes dominates the material's response to optical excitation influencing its electrical and optical properties such as charge formation and mobility. However, the effects of many-particle correlation have been relatively unexplored in perovskite because of the difficultly of probing these states directly. Here, we use double quantum coherence spectroscopy to explore the formation and localization of multiexciton states in these materials. Between the most confined domains, we demonstrate the presence of an interwell, two-exciton excited state. This demonstrates that the four-body Coulomb interaction electronically couples neighboring wells despite weak electron/hole hybridization in these materials. Additionally, in contrast with inorganic semiconductor quantum wells, we demonstrate a rapid decrease in the dephasing time as wells become thicker, indicating that exciton delocalization is not limited by structural inhomogeneity in low-dimensional perovskite.

19.
Adv Mater ; 29(33)2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-28671721

RESUMO

The tunable bandgap of colloidal quantum dots (CQDs) makes them an attractive material for photovoltaics (PV). The best present-day CQD PV devices employ zinc oxide (ZnO) as an electron transport layer; however, it is found herein that ZnO's surface defect sites and unfavorable electrical band alignment prevent devices from realizing their full potential. Here, chloride (Cl)-passivated ZnO generated from a solution of presynthesized ZnO nanoparticles treated using an organic-solvent-soluble Cl salt is reported. These new ZnO electrodes exhibit decreased surface trap densities and a favorable electronic band alignment, improving charge extraction from the CQD layer and achieving the best-cell power conversion efficiency (PCE) of 11.6% and an average PCE of 11.4 ± 0.2%.

20.
Nano Lett ; 17(6): 3701-3709, 2017 06 14.
Artigo em Inglês | MEDLINE | ID: mdl-28475344

RESUMO

Organo-metal halide perovskites are a promising platform for optoelectronic applications in view of their excellent charge-transport and bandgap tunability. However, their low photoluminescence quantum efficiencies, especially in low-excitation regimes, limit their efficiency for light emission. Consequently, perovskite light-emitting devices are operated under high injection, a regime under which the materials have so far been unstable. Here we show that, by concentrating photoexcited states into a small subpopulation of radiative domains, one can achieve a high quantum yield, even at low excitation intensities. We tailor the composition of quasi-2D perovskites to direct the energy transfer into the lowest-bandgap minority phase and to do so faster than it is lost to nonradiative centers. The new material exhibits 60% photoluminescence quantum yield at excitation intensities as low as 1.8 mW/cm2, yielding a ratio of quantum yield to excitation intensity of 0.3 cm2/mW; this represents a decrease of 2 orders of magnitude in the excitation power required to reach high efficiency compared with the best prior reports. Using this strategy, we report light-emitting diodes with external quantum efficiencies of 7.4% and a high luminescence of 8400 cd/m2.

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