Photoluminescence and LED application of β-SiAlON:Eu2+ green phosphor

We successfully prepared β-SiAlON:Eu²⁺ phosphors with composition of Eu_xSi_6?zAl_zO_yN_8?y (y = z ? 2x, x = 0.018, z = 0.23) by gas-pressured synthesis for application to LED. The crystal phase, microstructure, PL emission and thermal quenching properties were investigated in detail. The β-SiAlON:Eu²⁺ phosphors absorbed broad UV–vis spectral region, and showed a single intense broadband emission near 538 nm. The Stokes shift and zero-phonon line were calculated mathematically, and also estimated from the spectral data. The β-SiAlON:Eu²⁺ green phosphor showed superior thermal quenching properties compared to commercial silicate (SrBaSiO₄:Eu²⁺) green phosphor. The white light-emitting diode (LED) using the prepared β-SiAlON:Eu²⁺ green phosphor exhibited high color gamut, and good optical stability in high working temperature.     

Detailed assessment of mesh sensitivity for CFD simulation of coal combustion in a tangential-firing boiler

Journal of Mechanical Science and Technology - Computational fluid dynamics (CFD) has become an essential tool for optimizing the design and diagnosing the operation of a boiler. However, the...     

Modular Layer‐by‐Layer Assembly of Polyelectrolytes,Nanoparticles, and Molecular Catalysts into Solar‐to‐Chemical Energy Conversion Devices

The design and fabrication of solar‐to‐chemical energy conversion devices are enabled through interweaving multiple components with various morphologies and unique functions using a versatile layer‐by‐layer assembly method. Cationic and anionic polyelectrolytes are used as an electrostatic adhesive to assemble the following functional materials: plasmonic Ag nanoparticles for improved light harvesting, upconversion nanoparticles for utilization of near‐infrared light, and polyoxometalate water oxidation catalysts for enhanced catalytic activity. Polyelectrolytes also have an additional function of passivating the surface recombination centers of the underlying photoelectrode. These functional components are precisely assembled on a model photoanode (e.g., Fe₂O₃ and BiVO₄) in a desired order and various combinations without degradation of their intrinsic properties. As a result, the performance of water oxidation photoanodes is synergistically enhanced. This study can enable the design and fabrication of novel solar‐to‐chemical energy conversion devices.     

Tuning the spectrometric properties of white light by surface plasmon effect using Ag nanoparticles in a colour converting light-emitting diode

We report on the spectral tunability of white light by localized surface plasmon (LSP) effect in a colour converting hybrid device made of CdSe/ZnS quantum dots (QDs) integrated on InGaN/GaN blue light-emitting diodes (LEDs). Silver (Ag) nanoparticles (NPs) are mixed with QDs for generating LSP effect. When the plasmon absorption of Ag NPs is synchronized to the QW emission at 448 nm, the NPs selectively absorb the blue light and subsequently enhance the QD emission. Using this energy transfer scheme, the (x, y) chromaticity coordinates of the hybrid white LED was tuned from (0.32, 0.17) to (0.43, 0.26), and thereby generated warm white light emission with correlated colour temperature (CCT) around 1800 K. Moreover, a 47% enhancement in the external quantum efficiency (EQE) was realized.     

High-Performance Al–Sn–Zn–In–O Thin-Film Transistors: Impact of Passivation Layer on Device Stability

We fabricated high-performance thin-film transistors (TFTs) with an amorphous-Al–Sn–Zn–In–O (a-AT-ZIO) channel deposited by cosputtering using a dual Al–Zn–O and In–Sn–O target. The fabricated AT-ZIO TFTs, which feature a bottom-gate and bottom-contact configuration, exhibited a high field-effect mobility of 31.9 $ hbox{cm}^{2}/hbox{V}cdothbox{s}$, an excellent subthreshold gate swing of 0.07 V/decade, and a high $I_{{rm on}/{rm off}}$ ratio of $≫hbox{10}^{9}$, even below the process temperature of 250 $^{circ}hbox{C}$. In addition, we demonstrated that the temperature and bias-induced stability of the bottom-gate TFT structure can significantly be improved by adopting a suitable passivation layer of atomic-layer-deposition-derived $hbox{Al}_{2} hbox{O}_{3}$ thin film.      

Fluorobenzotriazole (FTAZ)‐Based Polymer Donor Enables Organic Solar Cells Exceeding 12% Efficiency

The fluorobenzotriazole (FTAZ)‐based copolymer donors are promising candidates for nonfullerene polymer solar cells (PSCs), but suffer from relatively low photovoltaic performance due to their unsuitable energy levels and unfavorable morphology. Herein, three polymer donors, L24 , L68 , and L810 , based on a chlorinated‐thienyl benzodithiophene (BDT‐2Cl) unit and FTAZ with different branched alkyl side chain, are synthesized. Incorporation of a chlorine (Cl) atom into the BDT unit is found to distinctly optimize the molecular planarity, energy levels, and improve the polymerization activity. Impressively, subtle side chain length of FTAZ realizes a dramatic improvement in all the device parameters, as revealed by the short‐current density (J_sc) improved from 7.41 to 20.76 mA cm^?2, fill‐factor from 36.3 to 73.5%, and even the open‐circuit voltage (V_oc) from 0.495 to 0.790 V. The best power conversion efficiency (PCE) of 12.1% is obtained from the L810‐based device, which is one of the highest values reported for FTAZ‐based PSCs so far. Notably, the corresponding external quantum efficiency curve keeps a very prominent value up to 80% from 500 to 800 nm. The notable performance is discovered from the reduced energy loss, improved molecular face‐on orientation, the down‐shifted energy levels, and optimized absorption coefficient regulated by side‐chain engineering.     

Reliable Piezoelectricity in Bilayer WSe2 for Piezoelectric Nanogenerators

Recently, piezoelectricity has been observed in 2D atomically thin materials, such as hexagonal‐boron nitride, graphene, and transition metal dichalcogenides (TMDs). Specifically, exfoliated monolayer MoS₂ exhibits a high piezoelectricity that is comparable to that of traditional piezoelectric materials. However, monolayer TMD materials are not regarded as suitable for actual piezoelectric devices due to their insufficient mechanical durability for sustained operation while Bernal‐stacked bilayer TMD materials lose noncentrosymmetry and consequently piezoelectricity. Here, it is shown that WSe₂ bilayers fabricated via turbostratic stacking have reliable piezoelectric properties that cannot be obtained from a mechanically exfoliated WSe₂ bilayer with Bernal stacking. Turbostratic stacking refers to the transfer of each chemical vapor deposition (CVD)‐grown WSe₂ monolayer to allow for an increase in degrees of freedom in the bilayer symmetry, leading to noncentrosymmetry in the bilayers. In contrast, CVD‐grown WSe₂ bilayers exhibit very weak piezoelectricity because of the energetics and crystallographic orientation. The flexible piezoelectric WSe₂ bilayers exhibit a prominent mechanical durability of up to 0.95% of strain as well as reliable energy harvesting performance, which is adequate to drive a small liquid crystal display without external energy sources, in contrast to monolayer WSe₂ for which the device performance becomes degraded above a strain of 0.63%.     

Printable and Rewritable Full Block Copolymer Structural Color

Structural colors (SCs) of photonic crystals (PCs) arise from selective constructive interference of incident light. Here, an ink‐jet printable and rewritable block copolymer (BCP) SC display is demonstrated, which can be quickly written and erased over 50 times with resolution nearly equivalent to that obtained with a commercial office ink‐jet printer. Moreover, the writing process employs an easily modified printer for position‐ and concentration‐controlled deposition of a single, colorless, water‐based ink containing a reversible crosslinking agent, ammonium persulfate. Deposition of the ink onto a self‐assembled BCP PC film comprising a 1D stack of alternating layers enables differential swelling of the written BCP film and produces a full‐colored SC display of characters and images. Furthermore, the information can be readily erased and the system can be reset by application of hydrogen bromide. Subsequently, new information can be rewritten, resulting in a chemically rewritable BCP SC display.     

Superior mechanical properties and strengthening mechanisms of lightweight AlxCrNbVMo refractory high-entropy alloys(x = 0, 0.5,1.0) fabricated by the powder metallurgy process

Light and strong AlxCrNbVMo(x=0,0.5,and 1.0) refractory high-entropy alloys(RHEAs) were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3 μm,and small amounts(4 vol.%) of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃ compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃ was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27 % and 87 % at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm~3,while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50 % of the yield strength of the AlxCrNbVMo RHEAs.     

Conflict detection and resolution for goal formation in the fractal manufacturing system

The fractal manufacturing system (FrMS) is based on the concept of autonomously cooperating agents referred to as fractals. A fractal is a set of self-similar agents whose goal can be achieved through cooperation, coordination, and negotiation among the agents for themselves. A fractal has fractal-specific characteristics (e.g. self-similarity, self-organization, self-optimization, goal-orientation, and dynamics), and it also has the characteristics of an agent (e.g. autonomy, mobility, intelligence, cooperation, and adaptability) at the same time. In the FrMS, a goal can be regarded as the status which the system aspires to be in. The goal-formation process (GFP) in the FrMS is a process of generating goals and modifying them by coordination between agents. In the GFP, conflicts may occur between goals, which can drive a system to become inefficient. In this paper, a conflict resolution mechanism via agent-based negotiation is proposed for facilitating the GFP. The scheme deals with non-fixed goals. The mobile agent-based negotiation process (MANPro), in which a mobile agent is used for information-exchanging and problem-solving, is used for negotiations in this scheme. The proposed mechanism is illustrated with a goal formation scenario in an exemplary FrMS.