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Phosphor Ceramics for High-power Solid-state Lighting
No full textDue to high power, high brightness, small size, energy saving, and environment friendliness, solid-state lighting has been becoming the most promising lighting technology in this century. As the key material of solid-state lighting, the luminescent properties of phosphors directly determine the crucial parameters such as the color rendering index, luminous efficacy and reliability of solid-state lighting devices. Compared with single crystals, phosphor glasses, phosphor films and quantum-well LEDs, phosphor ceramics have become the most excellent phosphor materials for high-power solid-state lighting due to its excellent thermal and optical properties and easy control of microstructure. In the future, phosphor ceramics is expected to be more widely used and developed in automotive headlights, outdoor lighting, laser TVs, laser cinema projectors, and other fields, and have a broad market prospect. In this review, design principles of high-power solid-state lighting phosphor ceramics are put forward firstly, and then their research progress of oxide phosphor ceramics (mainly refers to Y3Al5O12) and nitrogen/oxynitride phosphor ceramics are reviewed mainly. Finally, the development of phosphor ceramics for high-power solid-state lighting is prospected
Synthesis and properties of the bio-based isomeric benzoxazine resins: Revealing the effect of the neglected short alkyl substituents
No full textBio-based feedstocks usually contain many isomers with similar structures, and the short alkyl substituents are generally considered as low-reactive groups in benzoxazine chemistry due to their low induction effect and chemical inertness. Therefore, little attention has been paid on their effects on the synthesis or properties of benzoxazine. In this work, two bio-based benzoxazine isomers (CAR-fbz and THY-fbz) containing methyl and isopropyl groups with interchanged positions were synthesized from the renewable carvacrol and thymol. Their synthetic process, crystal features, and curing reactions were carefully investigated. Results showed that different side reacitions and by-products were detected under the same synthese conditions. And using the similar purification method, CAR-fbz and THY-fbz with high purity were found to have different crystal features. In addition, the cured systems also indicated varied H-bonding features and thermal properties based on differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA) results. With the help of density functional theory (DFT) calculation, the reasons were attributed to the different electrophilicity of phenol moiety, varied molecular symmetry and intermolecular interaction caused by the overlooked short alkyls. Summarily, the leverage of short-chain alkyl groups on benzoxazine chemistry is revealed. The result is significant for the benzoxazine synthesis, especially when the renewable compounds are taken as the starting materials for bio-based benzoxazine preparation, which often has many isomers with similar structures
Effect of the 345 degrees C and 16.5 MPa autoclave corrosion on the oxidation behavior of Cr-coated zirconium claddings in the high-temperature steam
No full textCr-coated Zirlo tubes were conducted in the autoclave corrosion (345 degrees C and 16.5 MPa), followed by the 1200 degrees C steam oxidation. After the 1-h oxidation, the coated tubes exhibited structural integrity, in contrast to the uncoated ones that had broken into pieces. Moreover, the coated tubes that already underwent the 45-days precorrosion, still remained good oxidation resistance with the weight gain of -4.46 mg/cm2. During the precorrosion, very thin Cr2O3 tissue formed on the outmost surface and along the columnar boundaries, which would suppress the formation of bubbles and cracks in the subsequent oxidation
Ultra-flexible light-permeable organic solar cells for the herbal photosynthetic growth
No full textUltra-flexible light-permeable organic solar cells (LP-OSCs) have attracted great attentions for their potential greenhouse applications. Herein, we reported for the first time the quantitative analysis of medicinal plants, photosynthetic efficiency and content of medicinal active ingredients, to evaluate the overall performance of the ultra-flexible OSC with high-transmission by simulating the greenhouse environment. In addition, ternary active layer strategy consisting of near-infrared (NIR) alloy acceptors was utilized for the LP-OSCs to effectively solve the trade-off between photovoltaic and optical properties. As a result, high efficiency of 15.1% and 12.04% for ultra-flexible opaque cell and devices with were obtained. The LP-OSCs based on ultra-flexible electrode with hierarchically photonic architectures had low incident light angle dependence which was beneficial for complex three-dimensional curved surface applications. Moreover, medicinal plants grown under ultra-flexible LP-OSCs displayed comparable growing tendency and pharmaceutical value with those grown under direct sunlight, which were studied based on the photosynthetic efficiency and content of medicinal active ingredients. This is the first report of the quantitative analysis of the effects of LP-OSCs on plant growth. Those results paved the way for realizing high-performing ultra-flexible LP-OSCs that could selectively absorb and transmit light for power generation and plants growth
High-performance Li-air battery after limiting inter-electrode crosstalk
No full textLi-air battery (LAB), the energy-storage technology with highest theoretical energy density, is still seriously challenged by poor energy efficiency and limited durability though plenty of progresses have been made. In this work, we demonstrate that high performance LAB operated in N-2-O-2 (78:22) atmosphere could be achieved after limiting the inter-electrode crosstalk. The Li+-filtration membrane placed between electrodes could tailor the side reactions on lithium and suppress the anodic consumption of solvents & additives. With the adoption of lab-made blocking layer, the optimal cells stably operate for 1500 cycles with energy efficiencies as high as 90 similar to 95%, significantly better than other energy-storage systems. This approach presents the necessity of inhibiting interelectrode crosstalk in LAB to the community, which shed light on the practical utilization of LAB as secondary batteries in the future
Highly thermal conductive red-emitting AlN-CaAlSiN3:Eu2(+) composite phosphor ceramics for high-power laser-driven lighting
No full textThermally robust red-emitting phosphor ceramics are urgently required for laser lighting and displays with high luminance and better color saturation. The most promising CaAlSiN3:Eu ceramics have a low thermal conductivity of 4.2 W m(-1) K-1 and a small luminance saturation of 0.5 W, making it hard to be used under high power laser irradiation. In this work, we incorporated AlN into the CaAlSiN3:Eu ceramic to produce red-emitting AlNCaAlSiN3:Eu composite phosphor ceramics by spark plasma sintering. The fully densified phosphor ceramics have the highest thermal conductivity reported so far (53.5 W m(-1) K-1), which is about 13 times higher than the reported one. The luminance saturation of the composite ceramics occurs at a high threshold of 4.2 W under blue laser excitation, enabling them to be used for high power laser lighting. This work provides an idea of tackling the microstructure of nitride phosphor ceramics and of preparing thermally robust red-emitting color converters
Hidden Charge Order in an Iron Oxide Square-Lattice Compound
No full textSince the discovery of charge disproportionation in the FeO2 square-lattice compound Sr3Fe2O7 by Mossbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained hidden to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe K-edge resonant x-ray scattering to demonstrate checkerboard charge order in the FeO2 planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on hidden order in other materials
Helium-induced damage in U3Si5 by first-principles studies
No full textUranium silicide U3Si5 has been explored as an advanced nuclear fuel component for light water reactor to enhance the accident tolerance. In this paper, in order to understand the fuel performance of U3Si5, the primary point defects, secondary point defects, and the dissolution of He gas were studied by first-principles methods. Compared with U atoms and another type of Si-2 atoms, Si-1 atoms far from intrinsic Si vacancies are more likely to form point defects, implying that Si vacancies are prone to form separate single vacancies rather than vacancy clusters in the initial stage. From the calculated anti-site defect energies, it can be predicted that non-stoichiometric U-rich phase of U3Si5 are more likely to be formed than Si-rich phase, which are consistent with the chemical analysis of experimentally sintered Si-lean U3Si5 sample. It can be found that a single He atom favors residence in the interstitial site in the U layer directly above/below the intrinsic vacancy. It can also be seen that Vac-U, Vac-Si-1, and Vac-Si-2 vacancies can energetically accommodate up to 4, 0, and 3 He atoms, respectively. The formation of secondary vacancy defects is strongly dependent on the helium concentration. The current results show that the He-filled vacancy can promote the formation of adjacent secondary vacancy, leading to the formation of gas bubbles. This work may provide theoretical insights into the He irradiation-induced damage in U3Si5 as well as provide valuable clues for improving the design of the UN-U3Si5 composite fuel
Single-component organic solar cells with over 11% efficiency
No full textAchieving stable high-efficiency single-component devices is a challenging problem in the field of organic photovoltaics. Recently in Joule, Min and co-workers reported a single-component organic solar cell using a conjugated donor-acceptor block copolymer (PBDB-T-b-PYT); a remarkable efficiency of 11.32% was realized with impressive photostability and storage stability
High thermal conductivity and low leakage phase change materials filled with three-dimensional carbon fiber network
No full textAs one of the most effective energy storage compounds, phase change materials (PCMS) play an important role in energy conservation and storage. However, the inherent poor thermal conductivity and liquid leakage of PCMS seriously limit their practical application. Polyethylene glycol center dot calcium chloride (PEG center dot CaCl2) phase change materials filled with three-dimensional carbon fiber network were prepared by liquid phase impregnation and hot pressing molding method. The experimental results show that carbon fiber network (CF felt) and PEG center dot CaCl2 complex structure increase the thermal conductivity and stability. The in-plane thermal conductivity of PEG center dot CaCl2/CF composite (47.73% carbon content) is 0.97 W/mK, about 103% higher than that of PEG. PEG center dot CaCl2/CF composite does not present leakage even heating at 80 degrees C for 45 min (35 degrees C higher than the melting point of pure PEG), showing low leakage ability. High thermal conductivity, low leakage and low density of this composite suggest a promising route for thermal storage applications