Bright Bifacial White-Light Illumination by Highly Deformable Electroluminescent Devices Based on Transparent Ionic-Hydrogel Electrodes and Quantum-Dot Color Conversion.

Deformable alternating-current electroluminescent (ACEL) devices are of increasing interest because of their potential to drive innovation in soft optoelectronics. Despite the research focus on efficient white ACEL devices, achieving deformable devices with high luminance remains difficult. In this study, this challenge is addressed by fabricating white ACEL devices using color-conversion materials, transparent and durable hydrogel electrodes, and high-k nanoparticles. The incorporation of quantum dots enables the highly efficient generation of red and green light through the color conversion of blue electroluminescence. Although the ionic-hydrogel electrode provides high toughness, excellent light transmittance, and superior conductivity, the luminance of the device is remarkably enhanced by the incorporation of a high-k dielectric, BaTiO3. The fabricated ACEL device uniformly emits very bright white light (489 cd m-2) with a high color-rendering index (91) from both the top and bottom. The soft and tough characteristics of the device allow seamless operation in various deformed states, including bending, twisting, and stretching up to 400%, providing a promising platform for applications in a wide array of soft optoelectronics.

I-III-VI Quantum Dots and Derivatives: Design, Synthesis, and Properties for Light-Emitting Diodes.

Quantum dots (QDs) are important frontier luminescent materials for future technology in flexible ultrahigh-definition display, optical information internet, and bioimaging due to their outstanding luminescence efficiency and high color purity. I-III-VI QDs and derivatives demonstrate characteristics of composition-dependent band gap, full visible light coverage, high efficiency, excellent stability, and nontoxicity, and hence are expected to be ideal candidates for environmentally friendly materials replacing traditional Cd and Pb-based QDs. In particular, their compositional flexibility is highly conducive to precise control energy band structure and microstructure. Furthermore, the quantum dot light-emitting diodes (QLEDs) exhibits superior prospects in monochrome display and white illumination. This review summarizes the recent progress of I-III-VI QDs and their application in LEDs. First, the luminescence mechanism is illustrated based on their electronic-band structural characteristics. Second, focusing on the latest progress of I-III-VI QDs, the preparation mechanism, and the regulation of photophysical properties, the corresponding application progress particularly in light-emitting diodes is summarized as well. Finally, we provide perspectives on the overall current status and challenges propose performance improvement strategies in promoting the evolution of QDs and QLEDs, indicating the future directions in this field.

Hydrogel-Based, Dynamically Tunable Plasmonic Metasurfaces with Nanoscale Resolution.

Flat metasurfaces with subwavelength meta-atoms can be designed to manipulate the electromagnetic parameters of incident light and enable unusual light-matter interactions. Although hydrogel-based metasurfaces have the potential to control optical properties dynamically in response to environmental conditions, the pattern resolution of these surfaces has been limited to microscale features or larger, limiting capabilities at the nanoscale, and precluding effective use in metamaterials. This paper reports a general approach to developing tunable plasmonic metasurfaces with hydrogel meta-atoms at the subwavelength scale. Periodic arrays of hydrogel nanodots with continuously tunable diameters are fabricated on silver substrates, resulting in humidity-responsive surface plasmon polaritons (SPPs) at the nanostructure-metal interfaces. The peaks of the SPPs are controlled reversibly by absorbing or releasing water within the hydrogel matrix, the matrix-generated plasmonic color rendering in the visible spectrum. This work demonstrates that metasurfaces designed with these spatially patterned nanodots of varying sizes benefit applications in anti-counterfeiting and generate multicolored displays with single-nanodot resolution. Furthermore, this work shows system versatility exhibited by broadband beam-steering on a phase modulator consisting of hydrogel supercell units in which the size variations of constituent hydrogel nanostructures engineer the wavefront of reflected light from the metasurface.

Production of juvenile masu salmon (Oncorhynchus masou) from spermatogonia-derived sperm and oogonia-derived eggs via intraperitoneal transplantation of immature germ cells.

No effective cryopreservation technique exists for fish eggs and embryos; thus, the cryopreservation of germ cells (spermatogonia or oogonia) and subsequent generation of eggs and sperm would be an alternative solution for the long-term preservation of piscine genetic resources. Nevertheless, in our previous study using rainbow trout, we showed that recipients transplanted with XY spermatogonia or XX oogonia produced unnatural sex-biased F1 offspring. To overcome these obstacles, we transplanted immature germ cells (XX oogonia or XY spermatogonia; frozen for 33 days) into the body cavities of triploid hatchlings, and the transplanted germ cells possessed a high capacity for differentiating into eggs and sperm in the ovaries and testes of recipients. Approximately 30% of triploid recipients receiving frozen germ cells generated normal salmon that displayed the donor-derived black body color phenotype, although all triploid salmon not receiving transplants were functionally sterile. Furthermore, F1 offspring obtained from insemination of the oogonia-derived eggs and spermatogonia-derived sperm show a normal sex ratio of 1:1 (female:male). Thus, this method presented a critical technique for practical conservation projects for other teleost fish species and masu salmon.

Genome-wide transcriptome profiling of the medicinal plant Zanthoxylum planispinum using a single-molecule direct RNA sequencing approach.

High-throughput RNA sequencing has revolutionized transcriptome-based studies of candidate genes, key pathways and gene regulation in non-model organisms. We analyzed full-length cDNA sequences in Zanthoxylum planispinum (Z. planispinum), a medicinal herb in major parts of East Asia. The full-length mRNA derived from tissues of leaf, early fruit and maturing fruit stage were sequenced using PacBio RSII platform to identify isoform transcriptome. We obtained 51,402 unigenes, with average 1781 bp per gene in 82.473 Mb gene lengths. Among 51,402, 3963 unigenes showed variety of isoform. By selection of one representative gene among each of the various isoforms, we finalized 46,306 unique gene set for this herb. We identified 76 cytochrome P450 (CYP450) and related isoforms that are of the wide diversity in the molecular function and biological process. These transcriptome data of Z. planispinum will provide a good resource to study metabolic engineering for the production of valuable medicinal drugs and phytochemicals.

Enhanced UV absorption of GaN photodiodes with a ZnO quantum dot coating layer.

Light absorption at the surface of a photodiode can be enhanced by employing nanostructures smaller than the wavelength of interest. In this study, a ZnO quantum dot (QD) coating layer was investigated for improving the light absorption of gallium nitride (GaN) ultraviolet (UV) photodiodes. A GaN surface coated with a ZnO QD solution exhibited significantly lower surface reflection than an uncoated GaN surface, which, in turn, improved the responsivity of the GaN photodiode. In comparison with other nanostructure or multilayer thin film processes, the proposed ZnO QD coating process is simple and effective in enhancing UV light absorption.

Electroluminescence from two I-III-VI quantum dots of A-Ga-S (A=Cu, Ag).

Together with III-V InP, chalcopyrite I-III-VI metal chalcogenides particularly with the compositions of A-B-S (A=Cu+, Ag+, B=In3+, Ga3+) are regarded as an emerging non-Cd class for synthesis of visible-emitting colloidal quantum dots (QDs) and the following fabrication of QD-light-emitting diodes (QLEDs). To date, the composition of I-III-VI QDs which were exploited for QLED fabrication remains highly limited, with most devices demonstrated from Cu-In-S-based ones. Herein, we explore the synthesis of two Ga-based I-III-VI QDs of Ag-Ga-S (AGS) and Cu-Ga-S (CGS) QDs and their application to QLED fabrication. Using cyan AGS/ZnS and azure CGS/ZnS core/shell QDs, all-solution-processed, multilayered QLEDs with a hybrid combination of organic hole transport layer and inorganic electron transport layer are fabricated and compared. We observe that CGS QLED by far outperforms in luminance and efficiency its AGS counterpart, which is ascribable to the differences in both electronic band structure and core/shell structure between two comparative QDs.

High-efficiency red electroluminescent device based on multishelled InP quantum dots.

We report on the synthesis of highly fluorescent red-emitting InP quantum dots (QDs) and their application to the fabrication of a high-efficiency QD-light-emitting diode (QLED). The core/shell heterostructure of the QDs is elaborately tailored toward a multishelled structure with a composition-gradient ZnSeS intermediate shell and an outer ZnS shell. Using the resulting InP/ZnSeS/ZnS QDs as an emitting layer, all-solution-processible red InP QLEDs are fabricated with a hybrid multilayered device structure having an organic hole transport layer (HTL) and an inorganic ZnO nanoparticle electron transport layer. Two HTLs of poly(9-vinlycarbazole) or poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenyl-amine), whose hole mobilities are different by at least three orders of magnitude, are individually applied for QLED fabrication and such HTL-dependent device performances are compared. Our best red device displays exceptional figures of merit such as a maximum luminance of 2849 cd/m2, a current efficiency of 4.2 cd/A, and an external quantum efficiency of 2.5%.

Improved electroluminescence of quantum dot light-emitting diodes enabled by a partial ligand exchange with benzenethiol.

In this study, benzenethiol ligands were applied to the surface of CdSe@ZnS core@shell quantum dots (QDs) and their effect on the performance of quantum dot light-emitting diodes (QD-LEDs) was investigated. Conventional long-chained oleic acid (OA) and trioctylphosphine (TOP) capping ligands were partially replaced by short-chained benzenethiol ligands in order to increase the stability of QDs during purification and also improve the electroluminescence performance of QD-LEDs. The quantum yield of the QD solution was increased from 41% to 84% by the benzenethiol ligand exchange. The mobility of the QD films with benzenethiol ligands approximately doubled to 2.42 × 10(-5) cm(2) V(-1) s(-1) from 1.19 × 10(-5) cm(2) V(-1) s(-1) compared to the device consisting of OA/TOP-capped QDs, and an approximately 1.8-fold improvement was achieved over QD-LEDs fabricated with bezenethiol ligand-exchanged QDs with respect to the maximum luminance and current efficiency. The turn-on voltage decreased by about -0.6 V through shifting the energy level of the QDs with benzenethiol ligands compared to conventional OA and TOP ligands.

Metabolite fingerprinting, pathway analyses, and bioactivity correlations for plant species belonging to the Cornaceae, Fabaceae, and Rosaceae families.

KEY MESSAGE: A multi-parallel approach gauging the mass spectrometry-based metabolite fingerprinting coupled with bioactivity and pathway evaluations could serve as an efficacious tool for inferring plant taxonomic orders. Thirty-four species from three plant families, namely Cornaceae (7), Fabaceae (9), and Rosaceae (18) were subjected to metabolite profiling using gas chromatography-time-of-flight-mass spectrometry (GC-TOF-MS) and ultrahigh performance liquid chromatography-linear trap quadrupole-ion trap-mass spectrometry (UHPLC-LTQ-IT-MS/MS), followed by multivariate analyses to determine the metabolites characteristic of these families. The partial least squares discriminant analysis (PLS-DA) revealed the distinct clustering pattern of metabolites for each family. The pathway analysis further highlighted the relatively higher proportions of flavonols and ellagitannins in the Cornaceae family than in the other two families. Higher levels of phenolic acids and flavan-3-ols were observed among species from the Rosaceae family, while amino acids, flavones, and isoflavones were more abundant among the Fabaceae family members. The antioxidant activities of plant extracts were measured using ABTS, DPPH, and FRAP assays, and indicated that extracts from the Rosaceae family had the highest activity, followed by those from Cornaceae and Fabaceae. The correlation map analysis positively links the proportional concentration of metabolites with their relative antioxidant activities, particularly in Cornaceae and Rosaceae. This work highlights the pre-eminence of the multi-parallel approach involving metabolite profiling and bioactivity evaluations coupled with metabolic pathways as an efficient methodology for the evaluation of plant phylogenies.

Color-by-blue display using blue quantum dot light-emitting diodes and green/red color converting phosphors.

We report a novel full-color display based on the generation of full-color by a highly efficient blue QD-LED light approach, or so called color-by-blue QD-LED display. This newly proposed color-by-blue QD-LED display combines a blue CdZnS/ZnS QD-LED blue subpixel and excitation source with front-emitting green/red phosphor subpixels. It is carefully estimated that the detailed display characteristics as well as full color-conversion and reasonable device efficiency of blue, green, and red satisfy the minimum requirements for display application. Also, we would like to emphasize that the proposed blue, green, and red device shows maximum luminance of 1570, 12920, and 3120 cd/m², respectively, luminous efficiency of 1.5, 12.1, and 2.5 cd/A, respectively, and external quantum efficiency of 6.8, 2.8, and 2.0%, respectively. It is expected that full color generation by color-by-blue QD-LED will lead to further technological advancements in the area of efficient and facile display applications.

All-solution-processed, multilayered CuInS2/ZnS colloidal quantum-dot-based electroluminescent device.

While significant progress of electroluminescent (EL) quantum dot light-emitting diodes (QD-LEDs) that rely exclusively on Cd-containing II-VI quantum dots (QDs) has been reported over the past two decades with respect to device processing and performance, devices based on non-Cd QDs as an active emissive layer (EML) remain at the early stage of development. In this work, utilizing highly luminescent colloidal CuInS2 (CIS)/ZnS QDs, all-solution-processed multilayered QD-LEDs are fabricated by sequentially spin depositing a hole transport layer of poly(9-vinlycarbazole), an EML of CIS/ZnS QDs, and an electron transport layer of ZnO nanoparticles. Our focus in device fabrication is to vary the thickness of the QD EML, which is one of the primary determinants in EL performance but has not been addressed in earlier reports. The device with an optimal EML thickness exhibits a peak luminance of 1564 cd/m2 and current efficiency of 2.52 cd/A. This record value in efficiency is higher by 3-4 times that of CIS QD-LEDs reported previously.

Quantum-dot-based white lighting planar source through downconversion by blue electroluminescence.

We report the unprecedented fabrication of a planar white lighting quantum dot light-emitting diode (QD-LED) through integrating a CdZnS QD-based blue electroluminescence (EL) device with a free-standing polymethyl methacrylate (PMMA) composite film embedded with orange-emitting Cu-In-S (CIS) green-greenish yellow-emitting Cu-In-Ga-S (CIGS) QDs. The hybrid device successfully generates bicolored white emission that comprises blue EL and downconverted QD photoluminescence. The hybrid QD-LEDs loaded with the composite film embedded with one type of QDs exhibit a limited white spectral coverage, consequently producing low values (<65) in color rendering index (CRI). Thus, the QD-PMMA film consisting of a blend of green CIGS and orange CIS QD downconverters is applied for obtaining a higher-CRI white light through the spectral extension, resulting in a much improved CRI of 75-77. Various EL performances of the hybrid planar white device versus the reference blue QD-LED are also characterized in details.

White lighting device from composite films embedded with hydrophilic Cu(In, Ga)S2/ZnS and hydrophobic InP/ZnS quantum dots.

Two types of non-Cd quantum dots (QDs)-In/Ga ratio-varied, green-to-greenish-yellow fluorescence-tuned Cu-In-Ga-S (CIGS) alloy ones, and red-emitting InP ones-are synthesized for use as down-converters in conjunction with a blue light-emitting diode (LED). Among a series of Ga-rich CI1-xGxS/ZnS core/shell QDs (x = 0.7, 0.8, and 0.9), CI0.2G0.8S/ZnS QD is chosen for the hydrophobic-to-hydrophilic surface modification via an in-situ ligand exchange and then embedded in a water-soluble polyvinyl alcohol (PVA). This free-standing composite film is utilized as a down-converter for the fabrication of a remote-type white QD-LED, but the resulting bi-colored device exhibits a cool white light with a limited color rendering index property. To improve white light qualities, another QD-polymer film of hydrophobic red InP/ZnS QD-embedding polyvinylpyrrolidone is sequentially stacked onto the CI0.2G0.8S/ZnS QD-PVA film, producing a unique dual color-emitting, flexible and transparent bilayered composite film. Tri-colored white QD-LED integrated with the bilayered QD film possesses an exceptional color rendering property through reinforcing a red spectral component and balancing a white spectral distribution.

Blue-Emissive ZnSeTe Quantum Dots and Their Electroluminescent Devices.

Over the last two decades, quantum-dot light-emitting diodes (QLEDs), also known as quantum dot (QD) electroluminescent devices, have gained prominence in next-generation display technologies, positioning them as potential alternatives to organic light-emitting diodes. Nonetheless, challenges persist in enhancing key device performances such as efficiency and lifetime, while those of blue QLEDs lag behind compared with green and red counterparts. In this Perspective, we discuss key factors affecting the photoluminescence characteristics of environmentally benign blue-emissive ternary ZnSeTe QDs, including composition, core/shell heterostructure, and surface ligand. Notably, we highlight the recent progress in breakthrough strategies to enhance blue QLED performance, examining the effects of the ZnSeTe QD attribute and device architecture on device performance. This Perspective offers insights into integrated aspects of QD material and device structure in overcoming challenges toward a high-performance blue ZnSeTe QLED.

Core-Shell Perovskite Quantum Dots for Highly Selective Room-Temperature Spin Light-Emitting Diodes.

Circularly polarized light (CPL) is a crucial light source with a wide variety of potential applications such as magnetic recording, and 3D display. Here, core-shell heterostructured perovskite quantum dots (QDs) for room-temperature spin-polarized light-emitting diodes (spin-LEDs) are developed. Specifically, a 2D chiral perovskite shell is deposited onto the achiral 3D inorganic perovskite (CsPbBr3 ) core. Owing to the chiral-induced spin selectivity effect, the spin state of the injected charge carriers is biased when they are transmitted through the 2D chiral shell. The spin-controlled carriers then radiatively recombine inside the CsPbBr3 emissive core, resulting in CPL emission. It is demonstrated that the (R)- and (S)-1-(2-(naphthyl)ethylamine) (R-/S-NEA) 2D chiral cations enhance the spin polarization degree due to their strong chiroptical properties. Systematical defect analyses confirm that 2D chiral cations (i.e., R-/S-NEA) successfully passivate halide vacancies at the surface of the CsPbBr3 QDs, thereby attaining a high photoluminescence quantum yield of 78%. Moreover, the spin-LEDs prepared with core-shell QDs achieve a maximum external quantum efficiency of 5.47% and circularly polarized electroluminescence with a polarization degree (PCP-EL ) of 12% at room temperature. Finally, various patterns fabricated by inkjet printing the core-shell QDs emit strong CPL, highlighting their potential as an emitter for next-generation displays.

Color-converting bilayered composite plate of quantum-dot-polymer for high-color rendering white light-emitting diode.

Highly bright CuInS2 quantum dots (QDs), whose emission is easily tuned in orange and greenish-yellow colors through manipulating the ZnS shelling procedure, are integrated with polymethyl methacrylate (PMMA) to obtain a free-standing composite plate of QD-polymer. The composite plate embedded with orange or greenish-yellow QDs is combined in a remote type with a blue light-emitting diode (LED). No color rendering index (CRI) value results when orange QDs are applied, whereas use of greenish-yellow QDs leads to a limited CRI of 72. A higher-color rendering QD-LED is demonstrated through a spectral extension by devising a unique bilayer-structured QD plate, where two types of QD are separately incorporated into each PMMA matrix, with a buffer layer of polymer blend inserted between them. The bilayered QD plate LED exhibits an improved CRI of 81, a high luminous efficacy of 71.2 lm/W at an input current of 20 mA, and exceptional high-stability luminescent characteristics against the variation of applied current.

Preparation of a photo-degradation- resistant quantum dot-polymer composite plate for use in the fabrication of a high-stability white-light-emitting diode.

We report on the synthesis of highly fluorescent double-ZnS-shell-capped, yellow-emitting Cu-In-S quantum dots (QDs) with a surprisingly high quantum yield of 92%, the preparation of a free-standing QD-polymethylmethacrylate composite plate, and the application of the QD plate in the fabrication of QD-based white-light-emitting diodes (WLEDs). A free-standing QD plate with QDs embedded uniformly inside a polymeric matrix is used to fabricate a remote-type, resin-free WLED. The QD plate-based WLED displays a high luminous efficiency; however, it suffers from a significantly unstable device performance due to QD degradation upon prolonged photo-excitation. An exceptional operational stability of the QD plate-based WLED is realized by generating hybrid double layers of an organic adhesion layer and a gas barrier layer of sol-gel-derived silica, rendering the QD plate impermeable to oxygen. Our success in achieving a color converter robust against photo-degradation and applying it in the fabrication of a reliable QD-based LED is greatly encouraging as regards the development of next-generation QD-based LED lighting sources.

Utilization of solvothermally grown InP/ZnS quantum dots as wavelength converters for fabrication of white light-emitting diodes.

This work reports on a simple solvothermal synthesis of InP/ZnS core/shell quantum dots (QDs) using a much safer and cheaper phosphorus precursor of tris(dimethylamino)phosphine than the most popularly chosen tris(trimethylsilyl)phosphine. The band gap of InP QDs is facilely controlled by varying the solvothermal core growth time (4 vs. 6 h) with a fixed temperature of 150 degrees C, and the successive solvothermal ZnS shelling at 220 degrees C for 6 h results in green- and yellow-emtting InP/ZnS QD with emission quantum yield of 41-42%. The broad size distribution of as-synthesized InP/ZnS QDs, which appears to be inherent in the current solvothermal approach, is improved by a size-selective sorting procedure, and the emission properties of the resulting size-sorted QD fractions are investigated. To produce white emission for general lighting source, a blue light-emitting diode (LED) is combined with non-size-soroted green or yellow QDs as wavelength converters. Furthermore, the QD-LED that includes a blend of green and yellow QDs is fabricated to generate a white lighting source with an enhanced color rendering performance, and its electroluminescent properties are characterized in detail.

Solvothermal preparation of yellow-emitting CuInS2/ZnS quantum dots and their application to white light-emitting diodes.

Based on the development of highly fluorescent colloidal quantum dots (QDs), their successful applications for the fabrication of lighting sources such as light-emitting diodes (LEDs) and lasing devices have been demonstrated. Here, CuInS2/ZnS core/shell QDs are facilely prepared by a two-step solvothermal route. Depending on the amount of a shell precursor of Zn stearate, fluorescent properties such as emission color and quantum yield (QY) of CuInS2/ZnS QDs are tunable and optimized. Yellow-emitting CuInS2/ZnS QD with a peak wavelength of 562 nm, QY of 81%, and emission bandwidth of 114 nm is chosen as an efficient blue-to-yellow downconverter for the fabrication of QD-based white LED (WLED). Various electroluminescent properties including luminous efficacy and color rendering index of QD-WLED are measured as a function of forward current up to 100 mA and described in details.