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Y-shaped donor-pi-acceptor based deep-blue electroluminescent material for Non-doped organic light emitting devices
No full textExtensive efforts have been put together to create deep-blue fluorophores with desired efficiency of organic light emitting devices (OLEDs). But, deep-blue fluorophores demonstrating high performance for non-doped OLEDs are yet finite in numbers. Herein, a Y-shaped donor-acceptor based fluorophore, 4',4 '',4'''-(1-phenyl-1H-imidazole-2,4,5-triyl)tris(N,N-diphenylbiphenyl-4-amine) (3TPAI) is constructed by integrating imidazole and triphenyl-amine moieties for OLEDs. Non-doped OLED device is constructed by applying 3TPAI as emissive layer which reveals deep-blue light at 443 nm. An EQE of 4.16% is attained with current efficiency (CE) of 5.1 cd/A and a power efficiency (PE) of 2.87 lm/W. High thermal stability is realized with decomposition temperature of more than 500 degrees C (T-d; 516 degrees C). This material reveals the bright future of imidazole based donor-pi-acceptor fluorophores for highly quality non-doped deep-blue OLEDs
Self-powered ultraviolet photodiode based on lateral polarity structure GaN films
No full textIn this work, we report on a self-powered ultraviolet photodiode realized using lateral polarity structure (LPS) GaN films. The opposite nature of the polarization charge yields different barrier heights at the standard Ni/Au Schottky contact interface of N-polar and III-polar GaN films. As a result, a natural nonzero built-in potential is obtained in the LPS GaN photodiode, which showed photoresponsivity even at 0 V applied bias. The self-powered mechanism inside such an LPS GaN photodiode is discussed in detail by a combination of simulation prediction and experimental validation. Furthermore, a variation in the doping concentration of the adjacent III- and N-polar GaN domain is shown to improve the photoresponsivity compared to the conventional III-polar photodiode. Thus, this work validates that the LPS GaN photodiode is a promising candidate to realize self-powered operation and a general design rule for the photodiode with in-plane built-in potential
Additive Manufacturing of Polyamide 66: Effect of Process Parameters on Crystallinity and Mechanical Properties
No full textIn this study, polyamide 66 (PA 66) filaments were prepared for fused filament fabrication (FFF). The effects of the process parameters on the mechanical properties, initial microstructures, dynamic mechanical behavior, and crystallinity of the samples were investigated. The samples obtained at high processing temperatures exhibited high crystallinity, high tensile strength, and low porosity. Almost fully dense samples with excellent mechanical properties were obtained under optimal conditions. The tensile strength of the samples improved by 29.5% (from 68.07 to 88.17 MPa) with an increase in the nozzle temperature from 270 to 290 degrees C. The elongation at break abruptly increased (from 2.38 to 13.17%), because of the plastic behavior of the material and strain hardening. X-ray diffraction results demonstrated that the crystallinity of PA 66, significantly improved (from 47.3 to 65.6%). In addition, the dynamic mechanical performance of the samples was significantly related to the raster angle. The samples fabricated at a raster angle of 0 degrees exhibited the best dynamic mechanical properties, followed by the 45 degrees and 90 degrees samples. The successful fabrication of PA 66 samples demonstrates the potential use of PA 66 for producing parts using FFF, and provides options for utilizing materials with improved performance for additive manufacturing applications in engineering
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
Facile synthesis of metal and alloy nanoparticles by ultrasound-assisted dealloying of metallic glasses
No full textMetal and alloy nanoparticles synthesized by chemical reduction have attracted increasing attention due to their superior physical, chemical, and biological properties. However, most chemical synthesis processes rely on the use of harsh reducing agents and complicated chemical ingredients. Herein, we report a novel reduction-agent-free and surfactant (stabilizer)-free strategy to synthesize Cu, Ag, Au, Cu-Pt, Cu-Au, Cu-Au-Pt-Pd, and Au-Pt-Pd-Cu nanoparticles by ultrasound-assisted dealloying of Mgbased metallic glasses. The formation mechanism of the metal and alloy nanoparticles is revealed by a detailed investigation of sequential intermediate products. We demonstrate that the glass-liquid phase transition of the initially dealloying metallic glasses, together with the synergistic effect of dealloying and ultrasound-driven ligament-breakage of small enough nanoporous intermediates, play key roles in preparing the uniformly dispersed metal and alloy nanoparticles. This approach greatly simplifies the up-scaling synthesis of monometallic and bimetallic nanoparticles, and also provides a general strategy for synthesizing unprecedented multimetallic nanoparticles. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology
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
To Clarify the Resilience of PEBA/MWCNT Foams via Revealing the Effect of the Nanoparticle and the Cellular Structure
No full textThe objective of this study is to clarify the resilience of the poly(ether-mb-amide)/multiwalled carbon nanotube (PEBA/MWCNT) composite foams from the perspectives of the nanoparticle and the cellular structure. The PEBA/MWCNT composites were prepared via a solution blending process with different contents of MWCNTs (0, 0.1, 1, and 5 wt %), and then the PEBA/MWCNT foams were prepared via a subsequent two-step batch foaming technique. The cyclic tensile test was performed with a universal testing machine, and the inelastic behavior of the composites and the foams was estimated based on the cyclic strain-stress curves. It was found that the incorporation of the MWCNT not only enhances the inelastic behavior of the composites via increasing the modulus but also brings in improved resilience of the foams compared to the composites via decreasing the cell size and increasing the cell density. The foam with 0.1 wt % content of MWCNT exhibits the best resilience. It is considered that the competition between the two effects of the nanoparticles of restricting chain mobility and altering the cellular structure might be the reason to bring the best resilience at a suitable content of the nanoparticles. The resilience of the foams with different contents of MWCNT showed no significant dependence on the expansion ratio and the modulus, which allows for their potential applications in the fields of high-end sport shoes and sports apparatus
Sandwiched structure of hot-deformed Nd-Fe-B permanent magnets processed by Nd-Cu eutectic alloys diffusion
No full textA series of sandwiched structures with different near-surface mass fractions x (x 1/4 3 wt%, 4 wt%, 5 wt%) was employed to develop high-coercivity hot-deformed Nd-Fe-B magnets by the addition of 2 wt% Nd-Cu eutectic alloys via adjusting the middle thickness and near-surface thickness. The designed magnet with a pronounced composite structure shows a 23% increase in coercivity with a 6% loss of remanence by adjusting the sandwiched structure at 4 wt% Nd-Cu eutectic alloys in the near-surface regions. The results indicate that the near-surface Nd-Cu-rich shell structure can effectively suppress the magnetization reversal of overall magnets, enhancing the coercivity. With the help of loading stress, Nd-Cu liquid enriched at the near-surface regions of the sample is infiltrated into the Nd-Cu-lean middle region, resulting in a concentration gradient. Microstructure characterizations further demonstrate that the infiltrated Nd-Cu eutectic plays a critical role in inhibiting grain growth and intergranular magnetic interaction. The optimized microstructure features suppress the reversed magnetization process, which makes a positive contribution to coercivity. 0 2020 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved
Y-shaped donor-pi-acceptor based deep-blue electroluminescent material for Non-doped organic light emitting devices
No full textExtensive efforts have been put together to create deep-blue fluorophores with desired efficiency of organic light emitting devices (OLEDs). But, deep-blue fluorophores demonstrating high performance for non-doped OLEDs are yet finite in numbers. Herein, a Y-shaped donor-acceptor based fluorophore, 4',4 '',4'''-(1-phenyl-1H-imidazole-2,4,5-triyl)tris(N,N-diphenylbiphenyl-4-amine) (3TPAI) is constructed by integrating imidazole and triphenyl-amine moieties for OLEDs. Non-doped OLED device is constructed by applying 3TPAI as emissive layer which reveals deep-blue light at 443 nm. An EQE of 4.16% is attained with current efficiency (CE) of 5.1 cd/A and a power efficiency (PE) of 2.87 lm/W. High thermal stability is realized with decomposition temperature of more than 500 degrees C (T-d; 516 degrees C). This material reveals the bright future of imidazole based donor-pi-acceptor fluorophores for highly quality non-doped deep-blue OLEDs
Analysis on deformation and texture formation mechanism of hot-deformed Nd-Fe-B magnets based on heterogeneous structure evolution
No full textIn this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed (HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the formation mechanism of c-axis texture. The results show that the platelet grains are formed in the fine-grain regions at the initial stage of the deformation. As the amount of deformation increases, the proportion of platelet grains increases and arranges gradually, causing the formation of c-axis texture, till the grain merging occurres when the deformation is excessive. It should be noted that the rare earth-rich phase in the fine-grained region slowly diffuses to the coarse-grained region where only grain growth can be observed during deformation. The deformation mechanism and formation of c-axis texture in HD Nd-Fe-B magnets can be deduced to be accomplished by the processes of dissolution-precipitation diffusion, grain rotation and grain arrangement, based on the characterization of microstructure and texture evolution. Also, approaches to optimize the preparation process and magnetic properties of the hot-deformed Nd-Fe-B magnets were discussed. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology