Onion-like multicolor thermally activated delayed fluorescent carbon quantum dots for efficient electroluminescent light-emitting diodes.

Carbon quantum dots are emerging as promising nanomaterials for next-generation displays. The elaborate structural design is crucial for achieving thermally activated delayed fluorescence, particularly for improving external quantum efficiency of electroluminescent light-emitting diodes. Here, we report the synthesis of onion-like multicolor thermally activated delayed fluorescence carbon quantum dots with quantum yields of 42.3-61.0%. Structural, spectroscopic characterization and computational studies reveal that onion-like structures assembled from monomer carbon quantum dots of different sizes account for the decreased singlet-triplet energy gap, thereby achieving efficient multicolor thermally activated delayed fluorescence. The devices exhibit maximum luminances of 3785-7550 cd m-2 and maximum external quantum efficiency of 6.0-9.9%. Importantly, owing to the weak van der Waals interactions and adequate solution processability, flexible devices with a maximum luminance of 2554 cd m-2 are realized. These findings facilitate the development of high-performance carbon quantum dots-based electroluminescent light-emitting diodes that are promising for practical applications.

Wet Chemical Synthesis of Ultrathin γ-Ga2O3 Quantum Wires Enabling Far-UVC Photodetection with Ultrahigh Selectivity and Sensitivity.

As compared to solar-blind ultraviolet (UV) photodetectors (PDs), far-UVC PDs not only show some irreplaceable advantages but also are more challenging to be developed. To solve this challenge, we report herein a soft template-assisted solvothermal route to synthesize ultrathin γ-Ga2O3 quantum wires (UQWs) with diameters down to 1-2 nm. These UQWs all exhibit a cluster-like absorption feature with a strong peak located between 190 and 230 nm and an edge below 250 nm, allowing highly selective absorption to far-UVC light. Notably, their normalized absorption coefficients were experimentally and theoretically confirmed to increase obviously with decreasing their diameters. Self-powered photoelectrochemical-type PDs based on Ga2O3 QWs of 1.7 nm diameter were therefore fabricated, exhibiting an excellent far-UVC detection performance with an unprecedented ultrahigh spectral selectivity (R210 nm/R250 nm = 452). As a proof of concept, this paper offers a new idea for developing ultrawide bandgap semiconductor materials and devices by leveraging a strong quantum confinement effect.

Perspectives on Development of Optoelectronic Materials in Artificial Intelligence Age.

Optoelectronic devices, such as light-emitting diodes, have been demonstrated as one of the most demanded forthcoming display and lighting technologies because of their low cost, low power consumption, high brightness, and high contrast. The improvement of device performance relies on advances in precisely designing novelty functional materials, including light-emitting materials, hosts, hole/electron transport materials, and yet which is a time-consuming, laborious and resource-intensive task. Recently, machine learning (ML) has shown great prospects to accelerate material discovery and property enhancement. This review will summarize the workflow of ML in optoelectronic materials discovery, including data collection, feature engineering, model selection, model evaluation and model application. We highlight multiple recent applications of machine-learned potentials in various optoelectronic functional materials, ranging from semiconductor quantum dots (QDs) or perovskite QDs, organic molecules to carbon-based nanomaterials. We furthermore discuss the current challenges to fully realize the potential of ML-assisted materials design for optoelectronics applications. It is anticipated that this review will provide critical insights to inspire new exciting discoveries on ML-guided of high-performance optoelectronic devices with a combined effort from different disciplines.

Highly Efficient Loading of Procaine on Water-Soluble Carbon Dots toward Long-Acting Anesthesia.

Safe and efficient local anesthetic delivery carriers are crucial for long-term anesthesia and analgesics in clinical treatment. But currently, most of the local anesthetic carriers still have some disadvantages such as low drug-loading capacity, drug leakage, and potential side effects. Here, we report red-emissive carbon dots (Cys-CDs) synthesized by choosing cysteine and citric acid as precursors, which contain a large and intact sp2-domain with rich hydrophilic groups around the edge. The special structure of Cys-CDs is conducive to the efficient loading of procaine (PrC) via strong π-π stacking interactions. Based on the strong noncovalent interactions between them, the PrC loaded on Cys-CDs achieved slow release in vitro and had a long-lasting nerve blocking effect in vivo, which is 4-fold more than that of free PrC. More importantly, PrC/Cys-CDs do not cause any toxicity and inflammation during treatment owing to slow release of PrC and good water solubility of Cys-CDs, thus demonstrating the potential clinical application of CDs in long-lasting analgesia.

Correction: pH-Responsive fluorescent graphene quantum dots for fluorescence-guided cancer surgery and diagnosis.

Correction for 'pH-Responsive fluorescent graphene quantum dots for fluorescence-guided cancer surgery and diagnosis' by Zetan Fan et al., Nanoscale, 2017, 9, 4928-4933, https://doi.org/10.1039/C7NR00888K.

The emergence and prospects of carbon dots with solid-state photoluminescence for light-emitting diodes.

The significant features of carbon dots (CDs), such as bright and tunable photoluminescence, high thermal stability, and low toxicity, endow them with tremendous potential for application in next generation optoelectronics. Despite great progress achieved in the design of high-performance CDs so far, the practical applications in solid-state lighting and displays have been retarded by the aggregation-caused quenching (ACQ) effect ascribed to direct π-π interactions. This review provides a comprehensive overview of the recent progress made in solid-state CD emitters, including their synthesis, optical properties and applications in light-emitting diodes (LEDs). Their triplet-excited-state-involved properties, as well as their recent advances in phosphor-converted LEDs and electroluminescent LEDs, are mainly reviewed here. Finally, the prospects and challenges of solid-state CD-based LEDs are discussed with an eye on future development. We hope that this review will provide critical insights to inspire new exciting discoveries on solid-state CDs from both fundamental and practical standpoints so that the realization of their potential in optoelectronic areas can be facilitated.

Valence-Engineered Oxidase-Mimicking Nanozyme with Specificity for Aromatic Amine Oxidation and Identification.

Oxidase-mimicking nanozymes with specificity for catalyzing oxidation of aromatic amines are of great significance for recognition of aromatic amines but rarely reported. Herein, Cu-A nanozyme (synthesized with Cu2+ as a node and adenine as a linker) could specifically catalyze oxidation of o-phenylenediamine (OPD) in Britton-Robinson buffer solution. Such a specific catalytic performance was also corroborated with other aromatic amines, such as p-phenylenediamine (PPD), 1,5-naphthalene diamine (1,5-NDA), 1,8-naphthalene diamine (1,8-NDA), and 2-aminoanthracene (2-AA). Moreover, the presence of salts (1 mM NaNO2, NaHCO3, NH4Cl, KCl, NaCl, NaBr, and NaI) greatly mediated the catalytic activity with the order of NaNO2 < blank ≈ NaHCO3 < NH4Cl ≈ KCl ≈ NaCl < NaBr < NaI, which was due to anions sequentially increasing interfacial Cu+ content via anionic redox reaction, while the effect of cations was negligible. With the increased Cu+ content, Km decreased and Vmax increased, indicating valence-engineered catalytic activity. Based on high specificity and satisfactory activity, a colorimetric sensor array with NaCl, NaBr, and NaI as sensing channels was constructed to identify five representative aromatic amines (OPD, PPD, 1,5-NDA, 1,8-NDA, and 2-AA) as low as 50 µM, quantitatively analyze single aromatic amine (with OPD and PPD as model analysts), and even identify 20 unknown samples with an accuracy of 100%. In addition, the performance was further validated through accurately recognizing various concentration ratios of binary, ternary, quaternary, and quinary mixtures. Finally, the practical applications were demonstrated by successfully discriminating five aromatic amines in tap, river, sewage, and sea water, providing a simple and feasible assay for large-scale scanning aromatic amine levels in environmental water samples.

Carbon Dots for Electroluminescent Light-Emitting Diodes: Recent Progress and Future Prospects.

Carbon dots (CDs), as emerging carbon nanomaterials, have been regarded as promising alternatives for electroluminescent light-emitting diodes (LEDs) owing to their distinct characteristics, such as low toxicity, tuneable photoluminescence, and good photostability. In the last few years, despite remarkable progress achieved in CD-based LEDs, their device performance is still inferior to that of well-developed organic, heavy-metal-based QDs, and perovskite LEDs. To better exploit LED applications and boost device performance, in this review, a comprehensive overview of currently explored CDs is presented, focusing on their key optical characteristics, which are closely related to the structural design of CDs from their carbon core to surface modifications, and to macroscopic structural engineering, including the embedding of CDs in the matrix or spatial arrangement of CDs. The design of CD-based LEDs for display and lighting applications based on the fluorescence, phosphorescence, and delayed fluorescence emission of CDs is also highlighted. Finally, it is concluded with a discussion regarding the key challenges and plausible prospects in this field. It is hoped that this review inspires more extensive research on CDs from a new perspective and promotes practical applications of CD-based LEDs in multiple directions of current and future research.

Carbon Quantum Dots with Near-Unity Quantum Yield Bandgap Emission for Electroluminescent Light-Emitting Diodes.

Carbon quantum dots (CQDs) feature bright and tunable photoluminescence, solution processability, and low toxicity, showing great potential in optoelectronics. However, the large-scale synthesis of CQDs with near-unity photoluminescence quantum yield (PLQY) has not been achieved so far. In this study, we perform radical-assisted synthesis of hexagon-shaped CQDs (H-CQDs) delivering near-unity PLQY (96 %). Experimental and theoretical analyses revealed that the large vertically oriented transition dipole moment of H-CQDs originating from high symmetry results in nearly 100 % PLQY. The H-CQDs also exhibited a high electron mobility of up to 0.07 cm2  V-1 s-1 . These properties enable the H-CQD-based light-emitting diodes with a high external quantum efficiency of 4.6 % and a record maximum brightness of over 11 000 cd m-2 . This study represents a significant advance that CQDs-based electroluminescent device can be utilized for potential display and lighting applications.

Carbon Dots with Guanidinium and Amino Acid Functional Groups for Targeted Small Interfering RNA Delivery toward Tumor Gene Therapy.

Small interfering RNA (siRNA)-based gene therapy represents a promising strategy for tumor treatment. Novel gene vectors that can achieve targeted delivery of siRNA to the tumor cells without causing any side effects are urgently needed. To this end, the large amino acid mimicking carbon dots with guanidinium functionalization (LAAM GUA-CDs) are designed and synthesized by choosing arginine and dopamine hydrochloride as precursors. LAAM GUA-CDs can load siRNA through the multiple hydrogen bonds between their guanidinium groups and phosphate groups in siRNA. Meanwhile, the amino acid groups at the edges of LAAM GUA-CDs endow them the capacity to target tumors. After loading siBcl-2 as a therapeutic agent, LAAM GUA-CDs/siBcl-2 has a high tumor inhibition rate of up to 68%, which is twice more than that of commercial Lipofectamine 2000. Furthermore, LAAM GUA-CDs do not cause side effect during antitumor treatment owing to their high tumor-targeting ability, thus providing a versatile strategy for tumor-targeted siRNA delivery and cancer therapy.

Buffer species-dependent catalytic activity of Cu-Adenine as a laccase mimic for constructing sensor array to identify multiple phenols.

Laccase mimics are multicopper oxidase highly important for biotechnology and environmental evaluation/remediation. However, buffer species-dependent catalytic activity is rarely investigated. Herein, through Cu2+ coordinating with adenine (A), gram-scale Cu-Adenine nanosheets are synthesized. As a laccase mimic, Cu-Adenine exhibits excellent catalytic performance in 10 mM Tris-HAc, and greatly decreases in 10 mM MES (4-morpholine ethanesulfonic acid) and further decreases in 10 mM HEPES (N-2-hydroxyethyl piperazine-N'-2-ethanesulfonic acid) (pH = 7, 25 °C). Moreover, upon gradually increasing NaCl to 500 mM, the catalytic activity further enhances. Such the buffer species/NaCl concentration-dependent catalytic activity is explained with the help of Km (Michaelis constant) and Vmax (maximum rate value) Based on the fact that Cu-Adenine could differentially catalyze phenolic substrates (2,4-dichlorophenol (2,4-DP), o-chlorophenol (o-CP), m-chlorophenol (m-CP), p-chlorophenol (p-CP), phenol and catechol), a colorimetric sensor array with three buffer solutions as sensing channels is designed for simultaneously discriminating 2,4-DP, o-CP, m-CP, p-CP, phenol and catechol as low as 10 µM, even quantifying 2,4-DP (as a model analyst). The performance is further validated through accurately identifying binary and ternary mixtures, and even 18 blind samples containing one of six phenols and ternary mixtures. Finally, the designed sensor array is successfully applied for identifying six representative phenols in various simulated water samples, presenting great potential and valuable applications for large-scale scanning levels of phenols in water samples.

Red Phosphorescent Carbon Quantum Dot Organic Framework-Based Electroluminescent Light-Emitting Diodes Exceeding 5% External Quantum Efficiency.

Carbon quantum dots (CQDs) have developed into prospective nanomaterials for next-generation lighting and displays due to their intrinsic advantages of high stability, low cost, and environmental friendliness. However, confined by the spin-forbidden nature of triplet state transitions, the highest theoretical value of external quantum efficiency (EQE) of fluorescent CQDs is merely 5%, which fundamentally limits their further application in electroluminescent light-emitting diodes (LEDs). Soluble phosphorescent CQDs offer a means of breaking the shackle to achieve efficient monochromatic electroluminescence, especially red emission, which is a pivotal constituent in full-color displays. Here, the synthesis of red (625 nm) phosphorescent carbon quantum dot organic frameworks (CDOFs) with a quantum yield of up to 42.3% and realization of high-efficiency red phosphorescent electroluminescent LEDs are reported. The LEDs based on the CDOFs exhibited a red emission with a maximum luminance of 1818 cd m-2 and an EQE of 5.6%. This work explores the possibility of a new perspective for developing high-performance CQD-based electroluminescent LEDs.

Plasmonic Hot Hole Extraction from CuS Nanodisks Enables Significant Acceleration of Oxygen Evolution Reactions.

Localized surface plasmon resonance (LSPR) is well known for its unique ability to tune the reactivity of plasmonic materials via photoexcitation; however, it is still an open question as to whether plasmonic holes can be directly extracted to drive valuable chemical reactions. Herein we give an affirmative answer by reporting an illumination-enhanced oxygen evolution reaction (OER) using CuS nanodisks (NDs) alone as the electrocatalyst. Impressively, under 1221 nm laser or xenon lamp illumination, an unprecedented reduction of OER overpotential was observed on the CuS ND-coated electrodes. Transient absorption combined with Mott-Schottky measurements disclosed that near-infrared (NIR) irradiation generated abundant hot holes from LSPR damping in the CuS NDs accounting for the remarkable OER performance enhancement. This is the first report on the direct utilization of plasmonic hot holes in CuS nanomaterials for boosting OER performance, opening up a new route to designing NIR-active photocatalysts/electrocatalysts by exploiting the unique LSPR properties.

Glucose oxidase decorated fluorescent metal-organic frameworks as biomimetic cascade nanozymes for glucose detection through the inner filter effect.

Metal-organic frameworks (MOFs) as a peroxidase mimic have been integrated with glucose oxidase (GOx) to achieve one-step glucose detection. However, limited by the loading amount of GOx, the performances of the developed glucose sensing assays still remain to be further improved to meet sensing requirements in diverse biological samples. Herein, with Fe3+ as the metal ion and 2-amino-benzenedicarboxylic acid as a ligand, a fluorescent Fe-based organic framework (NH2-MIL-101) with peroxidase-like activity was synthesized. Due to the large specific surface area (791.75 m2 g-1), 68 µg mg-1 GOx could be immobilized through the amidation coupling reaction, and the product was designated GOx@NH2-MIL-101. With OPD as the substrate, Gox@NH2-MIL-101 achieved highly efficient biomimetic cascade catalysis for one-step glucose detection through an inner filter effect: upon reacting with glucose, GOx@NH2-MIL-101 catalytically oxidized glucose using dissolved O2, and the produced H2O2 concurrently oxidized o-phenylenediamine (OPD) to oxidized OPD (oxOPD), accompanied by the fluorescence of GOx@NH2-MIL-101 at 456 nm being quenched and that of oxOPD at 565 nm being enhanced. With the fluorescent ratio F565/F456 used as a readout signal, a wide linear range of 0.1-600 µM was obtained, and the detection limit was 0.0428 µM. Based on the excellent selectivity and high stability of GOx@NH2-MIL-101, the developed assay was successfully applied to glucose detection in human serum and saliva, presenting potential applications in diverse biological samples and even medical diagnosis.

Gram-Scale Synthesis of Highly Efficient Rare-Earth-Element-Free Red/Green/Blue Solid-State Bandgap Fluorescent Carbon Quantum Rings for White Light-Emitting Diodes.

The negative impact of rare-earth elements (REEs) on the environment, limited supply and high cost prompt the need for REE-free phosphor-converted white light-emitting diodes (LEDs). Here, we report the gram-scale synthesis of red/green/blue solid-state bandgap fluorescent carbon quantum rings (R/G/B-SBF-CQRs) with high quantum yields up to 30-46 %. This was achieved using cyano-group-bearing p-phenyldiacetonitrile as precursor and forming carbon quantum rings of different diameters through the linkage of curved carbon quantum ribbons of different lengths. The results show the role of cyano groups in inducing the curvature of the carbon quantum ribbons for CQR formation and emission of stable solid-state bandgap fluorescence. R/G/B-SBF-CQRs-phosphor-based LEDs emitted warm white light with low CCT (3576 K), high CRI (96.6), and high luminous efficiency (48.7 lm W-1 ), comparable to REE-phosphor-based LEDs.

Fe-N/C single-atom nanozyme-based colorimetric sensor array for discriminating multiple biological antioxidants.

Identifying the species and concentrations of antioxidants is really important because antioxidants play important roles in various biological processes and numerous diseases. Compared with an individual sensor detecting a single antioxidant with limited specificity, a sensor array could simultaneously identify various antioxidants, in which 3-5 types of nanomaterials with peroxidase-like activity are absolutely necessary. Herein, as a single-atom nanozyme, Fe-N/C with oxidase-mimicking activity was applied to construct a triple-channel colorimetric sensor array: (1) Fe-N/C catalytically oxidized three substrates 3,3',5,5'-tetramethylbenzidine (TMB), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and o-phenylenediamine (OPD) to produce blue oxidized TMB (oxTMB), green oxidized ABTS (oxABTS) and yellow oxidized OPD (oxOPD), respectively; (2) with oxTMB, oxABTS and oxOPD as three sensing channels, a colorimetric sensor array was constructed for simultaneously discriminating glutathione (GSH), l-cysteine (l-Cys), ascorbic acid (AA), uric acid (UA), and melatonin (MT), even quantifying concentrations (with GSH as a model analyst). The performance of the sensor array was validated through accurately identifying 15 blind samples containing GSH, l-Cys, AA, UA and MT in buffer solution and human serum samples, and also in binary and ternary mixtures. This work proved that fabricating a single nanozyme-based sensor array was a simplified and reliable strategy for simultaneously probing multiple antioxidants.

Correction: Xing, G. et al.'s Diameter- and Length-Controlled Synthesis of Ultrathin ZnS Nanowires and Their Size-Dependent UV Absorption Properties, Photocatalytical Activities and Band-Edge Energy Levels. Nanomaterials 2019, 9, 220.

The authors wish to make the following corrections to this article [1][...].