Bright Multicolor Bandgap Fluorescent Carbon Quantum Dots for Electroluminescent Light-Emitting Diodes.
TL;DR: In this paper, a multicolor bandgap fluorescent carbon quantum dots (MCBF-CQDs) from blue to red with quantum yield up to 75% were synthesized using a solvothermal method.
Abstract: Multicolor bandgap fluorescent carbon quantum dots (MCBF-CQDs) from blue to red with quantum yield up to 75% are synthesized using a solvothermal method. For the first time, monochrome electroluminescent light-emitting diodes (LEDs) with MCBF-CQDs directly as an active emission layer are fabricated. The maximum luminance of blue LEDs reaches 136 cd m-2 , which is the best performance for CQD-based monochrome electroluminescent LEDs.
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TL;DR: CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties, and critical insights into facilitating their potential in various application fields are proposed.
Abstract: Despite the various synthesis methods to obtain carbon dots (CDs), the bottom-up methods are still the most widely administrated route to afford large-scale and low-cost synthesis. However, as CDs are developed with increasing reports involved in producing many CDs, the structure and property features have changed enormously compared with the first generation of CDs, raising classification concerns. To this end, a new classification of CDs, named carbonized polymer dots (CPDs), is summarized according to the analysis of structure and property features. Here, CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties. Furthermore, deep insights into the effects of synthesis on the structure/property features of CDs are provided. Herein, the synthesis methods of CDs are also summarized in detail, and the effects of synthesis conditions of the bottom-up methods in terms of the structures and properties of CPDs are discussed and analyzed comprehensively. Insights into formation process and nucleation mechanism of CPDs are also offered. Finally, a perspective of the future development of CDs is proposed with critical insights into facilitating their potential in various application fields.
631 citations
TL;DR: This work demonstrates multicolored narrow bandwidth emission from triangular CQDs with a quantum yield up to 54–72% and synthesizes these dots showing tunable emission color, high fluorescence and a narrow FWHM of only 30 nanometers, which will set the stage for developing next-generation high-performance C QDs-based light-emitting diodes.
Abstract: Carbon quantum dots (CQDs) have emerged as promising materials for optoelectronic applications on account of carbon’s intrinsic merits of high stability, low cost, and environment-friendliness. However, the CQDs usually give broad emission with full width at half maximum exceeding 80 nm, which fundamentally limit their display applications. Here we demonstrate multicolored narrow bandwidth emission (full width at half maximum of 30 nm) from triangular CQDs with a quantum yield up to 54–72%. Detailed structural and optical characterizations together with theoretical calculations reveal that the molecular purity and crystalline perfection of the triangular CQDs are key to the high color-purity. Moreover, multicolored light-emitting diodes based on these CQDs display good stability, high color-purity, and high-performance with maximum luminance of 1882–4762 cd m−2 and current efficiency of 1.22–5.11 cd A−1. This work will set the stage for developing next-generation high-performance CQDs-based light-emitting diodes.
592 citations
TL;DR: An ultraviolet (UV)-pumped CQD phosphors-based warm white light-emitting diode (WLED) is realized for the first time and achieves a color rendering index of 97.
Abstract: Red emissive carbon quantum dots (R-CQDs) with quantum yield of 53% is successfully prepared. An ultraviolet (UV)-pumped CQD phosphors-based warm white light-emitting diode (WLED) is realized for the first time and achieves a color rendering index of 97. This work provides a new avenue for the exploration of low cost, environment-friendly, and high-performance CQD phosphors-based warm WLEDs.
564 citations
TL;DR: A Progress Report, covering interdisciplinary aspects including material chemistry of quantum dots and charge-transporting layers, optimization and mechanism studies of prototype devices and processing techniques to produce large-area and high-resolution red-green-blue pixel arrays, identifies a few key challenges facing the development of active-matrix QLED displays.
Abstract: Quantum dots are a unique class of emitters with size-tunable emission wavelengths, saturated emission colors, near-unity luminance efficiency, inherent photo- and thermal- stability and excellent solution processability. Quantum dots have been used as down-converters for back-lighting in liquid-crystal displays to improve color gamut, leading to the booming of quantum-dot televisions in consumer market. In the past few years, efficiency and lifetime of electroluminescence devices based on quantum dots achieved tremendous progress. These encouraging facts foreshadow the commercialization of quantum-dot light-emitting diodes (QLEDs), which promises an unprecedented generation of cost-effective, large-area, energy-saving, wide-color-gamut, ultra-thin and flexible displays. Here we provide a Progress Report, covering interdisciplinary aspects including material chemistry of quantum dots and charge-transporting layers, optimization and mechanism studies of prototype devices and processing techniques to produce large-area and high-resolution red-green-blue pixel arrays. We also identify a few key challenges facing the development of active-matrix QLED displays.
548 citations
TL;DR: This Outlook comprehensively summarize the classification of CDs based on the analysis of their formation mechanism, micro-/nanostructure and property features, and describe their synthetic methods and optical properties including strong absorption, photoluminescence, and phosphorescence.
Abstract: Carbon dots (CDs), as a new type of carbon-based nanomaterial, have attracted broad research interest for years, because of their diverse physicochemical properties and favorable attributes like good biocompatibility, unique optical properties, low cost, ecofriendliness, abundant functional groups (e.g., amino, hydroxyl, carboxyl), high stability, and electron mobility. In this Outlook, we comprehensively summarize the classification of CDs based on the analysis of their formation mechanism, micro-/nanostructure and property features, and describe their synthetic methods and optical properties including strong absorption, photoluminescence, and phosphorescence. Furthermore, the recent significant advances in diverse applications, including optical (sensor, anticounterfeiting), energy (light-emitting diodes, catalysis, photovoltaics, supercapacitors), and promising biomedicine, are systematically highlighted. Finally, we envisage the key issues to be challenged, future research directions, and perspectives to show a full picture of CDs-based materials.
537 citations
References
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TL;DR: In this paper, a simple route to the production of high-quality CdE (E=S, Se, Te) semiconductor nanocrystallites is presented, based on pyrolysis of organometallic reagents by injection into a hot coordinating solvent.
Abstract: A simple route to the production of high-quality CdE (E=S, Se, Te) semiconductor nanocrystallites is presented. Crystallites from ∼12 A to ∼115 A in diameter with consistent crystal structure, surface derivatization, and a high degree of monodispersity are prepared in a single reaction. The synthesis is based on the pyrolysis of organometallic reagents by injection into a hot coordinating solvent. This provides temporally discrete nucleation and permits controlled growth of macroscopic quantities of nanocrystallites. Size selective precipitation of crystallites from Portions of the growth solution isolates samples with narrow size distributions (<5% rms in diameter). High sample quality results in sharp absorption features and strong «band-edge» emission which is tunable with particle size and choice of material
8,374 citations
TL;DR: It is reported that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state.
Abstract: We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.
3,817 citations
TL;DR: In this article, a hybrid organic/inorganic electroluminescent device was constructed based on the recombination of holes injected into a layer of semiconducting p-paraphenylene vinylene (PPV) with electrons injected into the multilayer film of cadmium selenide nanocrystals.
Abstract: ELECTROLUMINESCENT devices have been developed recently that are based on new materials such as porous silicon1 and semiconducting polymers2,3. By taking advantage of developments in the preparation and characterization of direct-gap semiconductor nanocrystals4–6, and of electroluminescent polymers7, we have now constructed a hybrid organic/inorganic electroluminescent device. Light emission arises from the recombination of holes injected into a layer of semiconducting p-paraphenylene vinylene (PPV)8–10 with electrons injected into a multilayer film of cadmium selenide nanocrystals. Close matching of the emitting layer of nanocrystals with the work function of the metal contact leads to an operating voltage11 of only 4V. At low voltages emission from the CdSe layer occurs. Because of the quantum size effect19–24 the colour of this emission can be varied from red to yellow by changing the nanocrystal size. At higher voltages green emission from the polymer layer predominates. Thus this device has a degree of voltage tunability of colour.
3,783 citations
Journal Article•
TL;DR: In this article, a hybrid organic/inorganic electroluminescent device was constructed based on the recombination of holes injected into a layer of semiconducting p-paraphenylene vinylene (PPV) with electrons injected into the multilayer film of cadmium selenide nanocrystals.
Abstract: ELECTROLUMINESCENT devices have been developed recently that are based on new materials such as porous silicon' and semiconducting polymers 2,3 . By taking advantage of developments in the preparation and characterization of direct-gap semiconductor nanocrystals 4-6 , and of electroluminescent polymers7, we have now constructed a hybrid organic/inorganic electroluminescent device. Light emission arises from the recombination of holes injected into a layer of semiconducting p-paraphenylene vinylene (PPV) 2-10 with electrons injected into a multilayer film of cadmium selenide nanocrystals. Close matching of the emitting layer of nanocrystals with the work function of the metal contact leads to an operating voltage" of only 4 V. At low voltages emission from the CdSe layer occurs. Because of the quantum size effect 19-24 the colour of this emission can be varied from red to yellow by changing the nanocrystal size. At higher voltages green emission from the polymer layer predominates. Thus this device has a degree of voltage tunability of colour.
3,285 citations
TL;DR: A facile and highoutput strategy for the fabrication of CDs, which is suitable for industrial-scale production and is almost equal to fluorescent dyes, is discussed.
Abstract: Fluorescent carbon-based materials have drawn increasing attention in recent years owing to exceptional advantages such as high optical absorptivity, chemical stability, biocompatibility, and low toxicity. These materials primarily include carbon dots (CDs), nanodiamonds, carbon nanotubes, fullerene, and fluorescent graphene. The superior properties of fluorescent carbon-based materials distinguish them from traditional fluorescent materials, and make them promising candidates for numerous exciting applications, such as bioimaging, medical diagnosis, catalysis, and photovoltaic devices. Among all of these materials, CDs have drawn the most extensive notice, owing to their early discovery and adjustable parameters. However, many scientific issues with CDs still await further investigation. Currently, a broad series of methods for obtaining CD-based materials have been developed, but efficient one-step strategies for the fabrication of CDs on a large scale are still a challenge in this field. Current synthetic methods are mainly deficient in accurate control of lateral dimensions and the resulting surface chemistry, as well as in obtaining fluorescent materials with high quantum yields (QY). Moreover, it is important to expand these kinds of materials to novel applications. Herein, a facile and highoutput strategy for the fabrication of CDs, which is suitable for industrial-scale production (yield is ca. 58%), is discussed. The QY was as high as ca. 80%, which is the highest value recorded for fluorescent carbon-based materials, and is almost equal to fluorescent dyes. The polymer-like CDs were converted into carbogenic CDs by a change from low to high synthesis temperature. The photoluminescence (PL) mechanism (high QY/PL quenching) was investigated in detail by ultrafast spectroscopy. The CDs were applied as printing ink on the macro/micro scale and nanocomposites were also prepared by polymerizing CDs with certain polymers. Additionally, the CDs could be utilized as a biosensor reagent for the detection of Fe in biosystems. The CDs were prepared by a hydrothermal method, which is described in the Supporting Information (Figure 1a; see also the Supporting Information, Figure S1). The reaction was conducted by first condensing citric acid and ethylenediamine, whereupon they formed polymer-like CDs, which were then carbonized to form the CDs. The morphology and structure of CDs were confirmed by analysis. Figure 1b shows transmission electron microscopy (TEM) images of the CDs, which can be seen to have a uniform dispersion without apparent aggregation and particle diameters of 2–6 nm. The sizes of CDs were also measured by atomic force microscopy (AFM; Figure S2), and the average height was 2.81 nm. From the high-resolution TEM, most particles are observed to be amorphous carbon particles without any lattices; rare particles possess well-resolved lattice fringes. With such a low carbon-lattice-structure content, no obvious D or G bands were detected in the Raman spectra of the CDs (Figure S3). The XRD patterns of the CDs (Figure 1c) also displayed a broad peak centered at 258 (0.34 nm), which is also attributed to highly disordered carbon atoms. Moreover, NMR spectroscopy (H and C) was employed to distinguish sp-hybridized carbon atoms from sp-hybridized carbon atoms (Figure S4). In the H NMR spectrum, sp carbons were detected. In the C NMR spectrum, signals in the range of 30–45 ppm, which correspond to aliphatic (sp) carbon atoms, and signals from 100–185 ppm, which are indicative of sp carbon atoms, were observed. Signals in the range of 170– 185 ppm, which correspond to carboxyl/amide groups, were also present. In the FTIR analysis of CDs, the following were observed: stretching vibrations of C OH at 3430 cm 1 and C H at 2923 cm 1 and 2850 cm , asymmetric stretching vibrations of C-NH-C at 1126 cm , bending vibrations of N H at 1570 cm , and the vibrational absorption band of C=O at 1635 cm 1 (Figure S5). Moreover, the surface groups were also investigated by XPS analysis (Figure 1d). C1s analysis revealed three different types of carbon atoms: graphitic or aliphatic (C=C and C C), oxygenated, and nitrous (Table S1). In the UV/Vis spectra, the peak was focused on 344 nm in an aqueous solution of CDs. In the fluorescence spectra, CDs have optimal excitation and emission wavelengths at 360 nm and 443 nm, and show a blue color under a hand-held UV lamp (Figure 2a). Excitation-dependent PL behavior was [*] S. Zhu, Q. Meng, Prof. J. Zhang, Y. Song, Prof. K. Zhang, Prof. B. Yang State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University Changchun, 130012 (P. R. China) E-mail: byangchem@jlu.edu.cn
3,095 citations