Facilely synthesized carbon dots and configurated light-emitting diodes with efficient electroluminescence.

Carbon dots (CDs) are recently emerging photoluminescence (PL) and electroluminescence (EL) emitters that are highly spotlighted in solid-state lighting. In this work, exceptional CDs with few defects, high carbonation, good film morphology and excitation wavelength-independent PL emission have been facilely synthesized and characterized with X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Superior EL emission from CDs has been demonstrated. With CDs as a single emissive layer, the light-emitting diode (LED) shows a maximum luminance of 19.34 cd m-2, luminous efficiency of 0.037 cd A-1, power efficiency of 0.039 lm W-1, and external quantum efficiency (EQE) of 0.031%. With poly(9-vinylcarbazole)/CDs as dual emissive layers, the LED shows a maximum luminance of 30.01 cd m-2, luminous efficiency of 0.089 cd A-1, power efficiency of 0.046 lm W-1, and EQE of 0.064%. The latter is better than the former because of the improved carrier balance and extended emission zone. The EL emission of both CD-based LEDs moves from the ultraviolet/blue emission of organics and/or interface emission to predominantly visible CD emission with increasing voltage. The evolution of EL and PL allows for a deeper understanding of the mechanism of CD emission and the advancement of CD-based LEDs.

Aggregation-based phase transition tailored heterophase junctions of AgInS2 for boosting photocatalytic H2 evolution.

Due to high defect tolerance and multiphase allowance, AgInS2 (AIS) quantum dots (QDs) provide chances for designing new type junctions via tailoring defects, size, or phase structure. These new type junctions potentially enhance photoelectric performance, such as photocatalytic H2 evolution (PHE). Here, ultra-small AIS QDs (∼1 nm) with well-defined exciton absorption were prepared aqueously via a reverse hot-injection procedure for the first time. A coalescence or fast aggregation-based growth was observed for coarsening at 95 or 135 ℃, respectively. XRD and TEM investigations revealed that the tetragonal-orthorhombic (t-o) phase transition occurred via aggregation-based growth. The studies on phase transition kinetics resulted in fine-tailoring on AIS polymorphs, favoring t-o AIS junctions. UV-vis absorption spectra confirm the double absorption edge of the t-o heterophase junction with enhanced visible absorption. Steady and transient PL spectra suggest improvements in carriers' separation/transfer in this t-o junction. As a result, the optimized t-o AIS shows superior photocatalytic H2 evolution rates of 1022 µmol. g-1. h-1, 51.1 times that of t-AIS or 3.8 times that of o-AIS. This work is expected to provide new insight for designing ternary alloyed QDs with strongly coupled interfaces for effective H2 generations.

Annealing-Insensitive, Alcohol-Processed MoOx Hole Transport Layer for Universally Enabling High-Performance Conventional and Inverted Organic Solar Cells.

At present, most solution-processed molybdenum oxide (s-MoOx) hole transport layers (HTLs) are still mainly used in conventional organic solar cells (OSCs) but unsuitable for inverted OSCs. Herein, we demonstrate for the first time an annealing-insensitive, alcohol-processed MoOx HTL that can universally enable high-performance conventional and inverted OSCs. The s-MoOx HTL is spin-coated from the MoOx nanoparticle dispersion in alcohol, where the MoOx nanoparticles are synthesized by simple nonaqueous pyrolysis conversion of MoO2(acac)2. The MoOx nanoparticles possess uniform and very small sizes of less than 5 nm and can be well dispersed in alcohol, so the s-MoOx HTLs on ITO and active layer both show an overall uniform and smooth surface, suitable for conventional and inverted OSCs. In addition, the s-MoOx HTL possesses decent optical transmittance and appropriate work function. Utilizing the s-MoOx HTL annealed between room temperature and 110 °C and PM6:Y6 active layer, the conventional OSCs show an excellent power conversion efficiency (PCE) of 16.64-17.09% and the inverted OSCs also show an excellent PCE of 15.74-16.28%, which indicate that the s-MoOx HTL could be annealing-insensitive and universal for conventional and inverted OSCs. Moreover, conventional and inverted OSCs with the s-MoOx HTLs annealed at 80 °C both exhibit optimal PCEs of 17.09 and 16.28%, respectively, which are separately superior than that of the PEDOT:PSS-based conventional OSCs (16.94%) and the thermally evaporated MoO3 (e-MoO3)-based inverted OSCs (16.03%). Under light soaking and storage aging in air, the unencapsulated inverted OSCs based on the s-MoOx HTL show similarly excellent ambient stability compared to the e-MoOx-based devices. In addition, the s-MoOx HTL also shows a universal function in conventional and inverted OSCs with PBDB-T:ITIC and PM6:L8-BO active layers. Notably, the s-MoOx-based conventional and inverted OSCs with the PM6:L8-BO active layer exhibit very excellent PCEs of 18.21 and 17.12%, respectively, which are slightly higher than those of the corresponding PEDOT:PSS-based device (18.17%) and e-MoO3-based device (17.00%). The annealing-insensitive, alcohol-processed MoOx HTL may be very promising for flexible and large-scale processing conventional/inverted OSCs.

Enhanced Visible Photocatalytic Hydrogen Evolution of KN-Based Semiconducting Ferroelectrics via Band-Gap Engineering and High-Field Poling.

In various ferroelectric-based photovoltaic materials after low-band-gap engineering, the process by which high-field polarization induces the depolarizing electric field (Edp) to accelerate the electron-hole pair separation in the visible light photocatalytic process is still a great challenge. Herein, a series of semiconducting KN-based ferroelectric catalytic materials with narrow multi-band gaps and high-field polarization capabilities are obtained through the Ba, Ni, and Bi co-doping strategy. Stable Edp caused by high-field poling enhanced the visible photocatalytic hydrogen evolution in a 0.99KN-0.01BNB sample with a narrow band gap and optimal ferroelectricity, which can be 5.4 times higher than that of the unpoled sample. The enhanced photocatalytic hydrogen evolution rate can be attributed to the synergistic effect of the significant reduction of the band gap and the high-field-polarization-induced Edp. The change in the band position in the poled sample further reveals that high-field poling may accelerate the migration of carriers through band bending. Insights into the mechanism by which catalytic activity is enhanced through high-field-polarization-induced Edp may pave the way for further development of ferroelectric-based catalytic materials in the photocatalytic field.

Constructing defect-related subband in silver indium sulfide QDs via pH-dependent oriented aggregation for boosting photocatalytic hydrogen evolution.

Surface engineering of quantum dots (QDs) plays critical roles in tailoring carriers' dynamics of I-III-VI QDs via the interplay of QDs in aggregates or assembly, thus influencing their photocatalytic activities. In this work, an aqueous synthesis and the followed pH tuned oriented assembly method are developed to prepare network-like aggregates, dispersion, or sheet-like assembly of GSH-capped Silver Indium Sulfide (AIS). FTIR, DLS, and HRTEM investigation revealed that surface protonation or deprotonation of QDs occurred at pH < 6 or pH > 12 favors the formation of network-like aggregates with various defects or sheet-like assembly with perfect crystal lattice, respectively, via the surface charge induced interaction among AIS QDs. Further UV-vis, steady and transient PL investigation confirm the narrowed band gaps and the prolonged PL lifetime of the acidic network-like aggregates. As a result, the optimized network-like aggregates (3.0-AIS) exhibits superior photocatalytic H2 evolution (PHE) rates (5.2 mmol·g-1·h-1), about 113 times that of alkaline sheet-like assembly (13.0-AIS) or 2.7 times higher than that of dispersed AIS QDs (AIS-8.0). The formation of defects and their roles in PHE mechanisms are discussed. This work is expected to give some new insight for designing efficient non-cadmium/non-novel metal I-III-VI photocatalysts for boosting PHE.

Cross-Linkable and Alcohol-Soluble Pyridine-Incorporated Polyfluorene Derivative as a Cathode Interface Layer for High-Efficiency and Stable Organic Solar Cells.

Device performance and commercialization of organic solar cells (OSCs) are strongly influenced by the characteristics of the interface layers. Cross-linked polymer interface layers with solvent-resistant properties are very compatible with large-area solution-processing methods of OSCs and may be beneficial to the environmental stability of OSCs due to the viscoelastic and cross-linked characteristics of the cross-linked polymer. In this work, a novel cross-linkable and alcohol-soluble pyridine-incorporated polyfluorene derivative, denoted as PFOPy, is synthesized and used as a cathode interface layer (CIL) in OSCs. For PFOPy, the pendant epoxy group can be effectively cross linked through cationic polymerization under thermal treatment and the pendant pyridine group can offer good alcohol solubility. Optical absorption tests of PFOPy films before/after washing by chloroform demonstrate the excellent solvent-resistance property for the cross-linked PFOPy film. Compared with the typical ZnO CIL, the cross-linked PFOPy CIL can also substantially reduce ITO's work function and form a better interface contact with the active layer. Utilizing an inverted device structure and a typical active layer of PM6:Y6, ZnO-based OSCs display an optimal power conversion efficiency (PCE) of 15.83% while PFOPy-based OSCs exhibit superior photovoltaic performance with an optimal PCE of 16.20%. Moreover, ZnO-based and PFOPy-based OSCs separately maintain 89% and 90% of the corresponding initial PCE after 12 h of illumination, indicating similarly excellent photostability. More importantly, after 26 complete thermal cycles, ZnO-based OSCs only maintain 81% of the initial PCE while PFOPy-based OSCs retain 92% of the initial PCE and exhibit obviously better thermal cycling stability, indicating that the cross-linked PFOPy CIL should offer stronger interface robustness against thermal cycling stress due to the viscoelastic and cross-linked characteristics of PFOPy. The impressive results indicate that the cross-linked PFOPy CIL would be a very promising CIL in OSCs.

Imaging features of inflammatory pseudotumor-like follicular dendritic cell sarcoma of the spleen.

BACKGROUND: Inflammatory pseudotumor (IPT)-like follicular dendritic cell sarcoma (FDCS) is an extremely rare malignant neoplasm. METHODS: Retrospective analysis of imaging features of splenic IPT-like FDCS, including ultrasonography, computed tomography (CT), and magnetic resonance (MR) and contrast-enhanced imaging were performed. RESULTS: When the masses were small, the ultrasound images showed homogeneous hypoechoic signals, clear boundaries, and complete capsules. Abdominal plain CT scans showed equal density (easy to miss diagnosis), unclear boundaries, and no capsules. Magnetic resonance images (MRI) showed slightly shorter T1, slightly shorter T2, and clear boundaries. When the masses were large, the ultrasound images still showed clear boundaries and complete capsules, but the echoes of the masses were not uniform, and some of the masses showed dendritic hyperechoic centers. Abdominal plain CT scans showed irregular low densities in the center (unclear boundaries) and equal densities in the periphery. MRI showed short T1 and T2, but the central signals were mixed. When the mass was accompanied by extensive necrosis, abdominal plain CT scan showed mostly cystic lesions and slight calcifications in low density lesions. Contrast-enhanced CT showed only moderate enhancement in peripheral and septal areas. MRI showed that T1 and T2 were mainly mixed signals. Contrast-enhanced MR showed moderate enhancement of peripheral areas and septum. CONCLUSIONS: This is the first report to describe the IPT manifestations of the spleen (ultrasonography, CT, and MR). The diagnosis of IPT can be made by combining three imaging features.

Aqueous synthesis of composition-tuned defects in CuInSe2 nanocrystals for enhanced visible-light photocatalytic H2 evolution.

The composition and defect tolerance of CuInSe2 (CISe) quantum dots (QDs) provide a scaffold to design defects via tailoring the elemental ratio or distributions for boosting photocatalytic H2 evolution (PHE). Herein, a ligand-assisted two-step aqueous method was developed to prepare defect CISe quantum dots for the first time. UV-vis, XPS, HRTEM, and HADDF investigations confirmed the typical double-absorption edges of copper vacancy defects and indium substituted at copper site defects in the structure constructed through initial synthesis tuned by Cu/In ratio and the ensued coarsening. The steady-transient PL suggested that the D-A recombination with prolonged PL lifetime dominated the emission of composition-optimized CuInSe2 with the Cu/In ratio of 1/4 (CISe-1/4). Further transient photocurrent and electrochemical impedance spectroscopy investigations demonstrated that surface defects in the structure favor the carriers' separation/transportation. The CISe-1/4 exhibited a superior PHE rate of 722 µmol g-1 h-1, about 23 times higher than that of the initially synthesized CISe-1/4 nucleus (31 µmol g-1 h-1), with a maximum apparent quantum efficiency (AQE) of 1.3%. The analysis of energy levels and the coulombic interaction energy of electron-hole (J e/h) based on Raman, extending UV-vis spectra investigations suggested that surface defects resulted in decreased J e/h of CISe-1/4, favoring the enhanced PHE of this structure. This work is expected to provide a reference for designing effective non-noble metal I-III-VI photocatalysts.

Application of spherical polyelectrolyte brushes microparticle system in flocculation and retention.

In this paper, a microparticle system consisting of cationic polyacrylamide (CPAM) and anionic spherical polyelectrolyte brushes (ASPB) is proposed to improve the retention of pulp suspension containing bleached reed kraft pulp and precipitated calcium carbonate (PCC). We first describe the preparation of ASPB. The ASPB, consisting of a carbon sphere (CS) core and a shell of sodium polystyrene sulfonate (PSSNa) brushes, was synthesized by surface-initiated polymerization. The structure and morphology of ASPB were characterized by Fourier-transform infrared spectrometry (FTIR), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Then, flocculation and retention of pulp suspension by a CPAM/ASPB dual-component system were examined. Our results indicate that more highly effective flocculation and higher retention efficiency could be achieved simultaneously by a CPAM/ASPB dual-component system when compared to the conventional microparticle system. Bridging flocculation and electrostatic attraction might be the main flocculation mechanism for CPAM/ASPB systems.

Design of C3 N4 -Based Hybrid Heterojunctions for Enhanced Photocatalytic Hydrogen Production Activity.

Semiconductors and metals can form an Ohmic contact with an electric field pointing to the metal, or a Schottky contact with an electric field pointing to the semiconductor. If these two types of heterojunctions are constructed on a single nanoparticle, the two electric fields may cause a synergistic effect and increase the separation rate of the photogenerated electrons and holes. Metal Ni and Ag nanoparticles were successively loaded on the graphitic carbon nitride (g-C3 N4 ) surface by precipitation and photoreduction in the hope of forming hybrid heterojunctions on single nanoparticles. TEM/high-resolution TEM images showed that Ag and Ni were loaded on different locations on C3 N4 , which indicated that during the photoreduction reaction Ag+ obtained electrons from C3 N4 in the reduction reaction, whereas oxidation reactions proceeded on Ni nanoparticles. Photocatalytic hydrogen production experiments showed that C3 N4 -based hybrid heterojunctions can greatly improve the photocatalytic activity of materials. The possible reason is that two heterojunctions could form a long-range electric field similar to the p-i-n structure in semiconductors. Most of the photogenerated carriers were generated and then separated in this electric field, thereby increasing the separation rate of electrons and holes. This further improved the photocatalytic activity of C3 N4 .

Homo- and Heterovalent Doping-Mediated Self-Trapped Exciton Emission and Energy Transfer in Mn-Doped Cs2Na1-xAgxBiCl6 Double Perovskites.

Double perovskites exhibit low toxicity, intrinsic thermodynamic stability, and small carrier effective mass. Herein, a novel doping route was adopted to incorporate Mn ions into Cs2Na1-xAgxBiCl6 double perovskites for engineering the band gap and tailoring the energy transfer. The as-prepared Cs2Na1-xAgxBiCl6 (0 < x < 1) exhibited excellent photoluminescence and a broad self-trapped exciton (STE) band from 500 to 900 nm, which exhibited an abnormal emission peak blue shift with increasing temperature. For Mn-doped Cs2Na1-xAgxBiCl6, the two photoluminescence (PL) bands from d-d transition emission of Mn ions and STEs were always observed simultaneously in the PL window. The distinct energy-transfer channel from the Mn2+ ion guest to the double-perovskite host resulted in the dominant Mn2+ emission. Our results will be helpful for further understanding the nature of the photophysics of double perovskites.

Oriented assembly of CdS nanocrystals via dynamic surface modification-tailored particle interaction.

The controlled assembly of quantum dots (QDs) remains a challenge due to the lack of in-depth understanding of the roles of ligand dynamics. In this study, tripods, particles, nanorods and nanoflowers of CdS with yellow, red and cyan PL emissions, respectively, were achieved through the coarsening of thioglycolic acid (TGA)-capped CdS QDs with a novel hydroxyl-TGA exchange procedure. Dynamic hydroxyl modification-induced aggregation and coalescence can help to describe the defects and the corresponding photoluminescence characteristics of these nanocrystals. A crystal growth model involving assembly and coalescence was developed to describe the crystal growth and the corresponding PL properties, where hydroxyl-motivated hydrogen-bonding interaction was used to explain the oriented assembly of CdS QDs.

Aggregation-based abrupt crystallization from amorphous Ag2S to Ag2S nanocrystals.

Abrupt crystallization from ∼2-5 nm (amorphous) to ∼12-15 nm (crystalline) was observed in hydrothermal coarsening of Ag2S. The desorption behavior of capping ligands could be associated with the aggregation and fusion of amorphous particles into crystals.

Self-assembly of SnO2 quantum dots into hierarchically ordered structures assisted by oriented attachment.

Taking SnO2 quantum dots with random orientation as a precursor, NaOH induces self-assembly of SnO2 dots to form the nanowires, side-by-side attachment of which generates hierarchically ordered structures. The multistep oriented attachment mechanism can help to describe the oriented assembly of big nanocrystals.

The relationship between photoluminescence (PL) decay and crystal growth kinetics in thioglycolic acid (TGA) capped CdTe quantum dots (QDs).

The PL lifetime optimization of CdTe QDs capped with TGA has yet to be understood from a perspective of growth kinetics. In this work, the growth kinetics and PL properties of CdTe QDs growing in aqueous solutions of two TGA concentrations, 0 mM and 57 mM, were systematically investigated using UV, TEM, and PL methods. CdTe QDs in 0 mM TGA solution were found to follow the mixed OA (Oriented Attachment)-OR (Ostwald Ripening) growth kinetics. The PL peaks experienced a red-shift with almost unchanged intensity and the PL lifetimes increased gradually. In 57 mM TGA solution, the QDs followed the OA dominated growth mechanism. The PL peak broadened greatly with a red-shift and its intensity decreased significantly. The PL lifetime increased much higher than that in 0 mM TGA solution. Based on the different growth kinetic models of the two systems, we suggest that in the low (0 mM) TGA solution, the increased surface defects induced by TGA desorption and the existence of partial internal defects caused by OA growth were the main reasons for the gradual increase of PL lifetime, while in high (57 mM) TGA solution, the increase of PL lifetime was ascribed to the abundant internal defects produced by OA collision. Finally, kinetic data showed the effect of the TGA concentration on crystal growth and PL lifetime of CdTe QDs. The results might provide guidance for understanding the mechanism behind the phenomena of ligand-related PL properties.