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Effects of water molecules on luminescence in europium and terbium coordination polymers with p-fluorobenzoic acid as ligand

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Journal of Rare Earths 2024年第7期42卷 1258-1264页

作者： Xiaoqi Zhao Puyan Hao Yami Ling Mengzhen Jia Rui Zhu Jiawen Liu Qiang Xu Jianhong Zhou Collaborative Innovation Center of Rare-Earth Optical Functional materials and Devices Development Baoji Key Laboratory of Micro-Nano Optoelectronics and Terahertz TechnologySchool of Physics and Opto-Electronic TechnologyBaoji University of Arts and Sciences

Our previous experimental observations show that the crystal structure of lanthanide luminescent complexes synthesized in aqueous solution usually contains a large number of coordination water molecules or free water molecules.In order to probe the influence of water molecules on luminescent processes of lanthanide complexes,the photoluminescence properties of Ln-FBA（Ln=Eu and Tb,FBA=p-fluorobenzoic acid） coordination polymers at different ambient temperatures,in different solvents and aqueous DMSO solutions with different volume concentrations were systematically investigated.The experiment results show that the presence of water molecules can promote the energy transfer from FBA ligand to Ln3+,at the same time,can cause luminescent non-radiation quenching of lanthanide ions.In addition,the variation of emission intensity ratio of 615 nm/591 nm peaks of Eu3+with increasing the volume concentration of H2O can be potentially used for the quantitatively detection of water traces in organic solve nts.In order to suppress the non-radiation quenching caused by the water molecules,Ln-FBA（Ln=Eu and Tb） coordination polymers were embedded into the PVP matrix to prepare Ln-FBA@PVP hybrid materials.The photoluminescence investigation indicates that PVP can not only block the quenching effect of water molecules on luminescence,but also effectively sensitize Eu3+and Tb3+luminescence.These experimental conclusions are useful for probing the influence of water molecules on luminescent processes of lanthanide complexes,quantitatively detecting water traces in organic solvents and enhancing the photoluminescence intensity in lanthanide complexes.

关键词： Lanthanide complexes Luminescent quenching Photoluminescence Rare earths

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Discovery of strong bulk Dzyaloshinskii-Moriya interaction in composition-uniform centrosymmetric magnetic single layers

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Science China(Physics,Mechanics & Astronomy) 2024年第2期67卷 174-180页

作者： Lijun Zhu David Lujan Xiaoqin Li State Key Laboratory of Superlattices and Microstructures Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China college of materials Science and opto-electronic technology University of Chinese Academy of SciencesBeijing 100049China Department of Physics Center for Complex Quantum SystemsUniversity of Texas at AustinAustin 78712USA

Dzyaloshinskii-Moriya interaction(DMI)is the key ingredient of chiral spintronic phenomena and the emerging technologies based on such phenomena.A nonzero DMI usually occurs at magnetic interfaces or within non-centrosymmetric single crystals.Here,we report the observation of a strong unexpected DMI within a centrosymmetric polycrystalline ferromagnet that has neither a crystal inversion symmetry breaking nor a composition gradient.This DMI is a bulk effect,increases with the thickness of the magnetic layer,and is insensitive to the symmetry of the interfaces or the neighboring materials.We observe a total DMI strength that is a factor of>2 greater than the highest interfacial DMI in the literature.This DMI most likely arises from the strong spin-orbit coupling,strong orbital hybrization,and a“hidden”long-range asymmetry in the material.Our discovery of the strong unconventional bulk DMI in centrosymmetric,composition-uniform magnetic single layers provides fundamental building blocks for the emerging field of spintronics and will stimulate the exploitation of unconventional spin-orbit phenomena in a wide range of materials.

关键词： Brillouin light scattering Dzyaloshinskii-Moriya interaction spin wave

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Cationic ordering transition in oxygen-redox layered oxide cathodes

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Carbon Energy 2024年第1期6卷 197-206页

作者： Xinyan Li Ang Gao Qinghua Zhang Hao Yu Pengxiang Ji Dongdong Xiao Xuefeng Wang Dong Su Xiaohui Rong Xiqian Yu Hong Li Yong-Sheng Hu Lin Gu Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijingChina college of materials Science and opto-electronic technology University of Chinese Academy of SciencesBeijingChina Beijing National Center for Electron Microscopy and Laboratory of Advanced materials School of Materials Science and EngineeringTsinghua UniversityBeijingChina Beijing Advanced Innovation Center for materials Genome Engineering Huairou DivisionInstitute of PhysicsChinese Academy of SciencesBeijingChina

Understanding the structural origin of the competition between oxygen 2p and transition-metal 3d orbitals in oxygen-redox(OR)layered oxides is eminently desirable for exploring reversible and high-energy-density Li/Na-ion cathodes.Here,we reveal the correlation between cationic ordering transition and OR degradation in ribbon-ordered P3-Na_(0.6)Li_(0.2)Mn_(0.8)O_(2) via in situ structural analysis.Comparing two different voltage windows,the OR capacity can be improved approximately twofold when suppressing the in-plane cationic ordering transition.We find that the intralayer cationic migration is promoted by electrochemical reduction from Mn^(4+)to Jahn–Teller Mn^(3+)and the concomitant NaO_(6) stacking transformation from triangular prisms to octahedra,resulting in the loss of ribbon ordering and electrochemical decay.First-principles calculations reveal that Mn^(4+)/Mn^(3+)charge ordering and alignment of the degenerate eg orbital induce lattice-level collective Jahn–Teller distortion,which favors intralayer Mn-ion migration and thereby accelerates OR degradation.These findings unravel the relationship between in-plane cationic ordering and OR reversibility and highlight the importance of superstructure protection for the rational design of reversible OR-active layered oxide cathodes.

关键词： cationic ordering layered oxide cathodes oxygen redox sodium-ion batteries

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Deciphering the role of rGO in tuning dielectric properties of Er_(2)O_(3)/ZnO/rGO nanocomposites synthesized via facile approach

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Journal of Rare Earths 2024年第3期42卷 578-585,I0006页

作者： Saiqa Hafeez Saima Perveen Muhammad Zarrar Khan Awab Hashmi Fahad Azad School of Natural sciences(SNS) National University of Sciences and Technology(NUST)IslamabadPakistan electronic and Magnetic materials Laboratory School of Chemical and Materials Engineering(SCME)National University of Sciences and Technology(NUST)IslamabadPakistan

The present research investigated the effect of reduced graphene oxide(rGO) integration with assynthesized Er_(2)O_(3)/ZnO nanocomposites on dielectric properties. The samples were characterized by Xray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), diffuse reflectance spectroscopy(DRS), and energy dispersive spectroscopy(EDS). Complex impedance spectroscopy was utilized to characterize dielectric relaxation phenomena in Er_(2)O_(3)/ZnO and Er_(2)O_(3)/ZnO/rGO nanocomposites. All the samples exhibit single relaxation phenomena which are ascribed to grain boundaries. The addition of rGO to Er_(2)O_(3)/ZnO nanocomposite results in the enhancement of dielectric response due to increased local field intensity caused by the formation of conductinginsulating interfaces. Furthermore, the AC conductivity of the Er_(2)O_(3)/ZnO/rGO is increased at higher frequencies due to the presence of free charge carriers in rGO. At higher frequencies, Er_(2)O_(3)/ZnO/rGO nanocomposite with increased concentration of ZnO exhibits a more stable dielectric constant with extremely low dielectric loss. Hence, the inclusion of rGO in Er_(2)O_(3)/ZnO nanocomposites makes it a novel prospective candidate in the field of energy storage devices.

关键词： Erbium oxide(Er_(2)O_(3)) Rare earths Stable dielectric constant Impedance Polarization Grain boundaries

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A novel long persistent luminescent material CaGeO3:Tb3+ with photo-stimulation properties

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Journal of Rare Earths 2024年第7期42卷 1233-1239页

作者： Wei Meng Xiaoyan Fu Tongyan Lin Zewen Liu Naihui Chen Jiaxu Zhang Runyao Liu Rujun Yang Long Chen Hongwu Zhang School of Chemistry and Material sciences Ludong University college of materials Science and Engineering Xiamen University of Technology college of materials Xiamen University

A novel green long afterglow material CaGeO3:Tb3+was synthesized by high temperature solid phase method.According to the experimental results,CaGeO3:Tb3+is a green long persistent luminescent（LPL）material with excellent performance.CaGeO3:Tb3+shows LPL emission peak at 442,490.9,548.7,588.5and 623.8 nm,corresponding to5D3to7F4and5D4to7FJ（J=6,5,4,3） transitions of Tb3+,Its CIE coordinates are（0.27,0.50）,indicating that the afterglow emission is close to the light of green region.In addition,after the excitation source is turned off,the afterglow time is longer than 90 min.After an interval of 7 h,the photo-stimulation luminescence（PSL） can be observed by using 980 nm laser cyclic excitation.The thermoluminescence（ThL） results show that there are three types of traps in the material and their depths are 0.666,0.774 and 0.892 eV respectively,which are caused by the doping of Tb3+.All the results show that CaGeO3:Tb3+is an excellent long afterglow luminescent material.

关键词： CaGeO3:Tb3+ Long persistent luminescence Photo-stimulation Rare earths Trap

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Advancements in the modification of magnesium-based hydrogen storage materials

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Progress in Natural Science:materials International 2024年第3期34卷 540-554页

作者： Lin Yang Wen Zeng Yanqiong Li college of materials Science and Engineering Chongqing University School of electronic Information & Electrical Engineering Chongqing University of Arts and Sciences

Magnesium-based hydrogen storage materials represent a hydrogen storage technology with broad application prospects. As the global energy crisis and environmental pollution issues become increasingly severe, hydrogen,as a clean and efficient energy source, has garnered growing attention. Magnesium-based hydrogen storage,serving as a crucial means for storing and transporting hydrogen, is gaining prominence due to its abundant resources, low cost, low density, and high hydrogen storage density. However, challenges in terms of absorption/desorption rates, temperature, activation energy, and enthalpy during hydrogen application impede its development. To address these challenges, this paper systematically reviews current research on magnesium-based hydrogen storage materials, encompasses their types, characteristics, and hydrogen absorption mechanisms.Furthermore, it delves into the impacts of nanoscale dimensions, alloying, doping, and catalysis on the performance of magnesium-based materials. The aim is to provide valuable insights for research in related fields.

关键词： For hydrogen storage Magnesium-based materials Research on modifying

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Joint UAV trajectory and communication design with heterogeneous multi-agent reinforcement learning

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Science China(Information sciences) 2024年第3期67卷 225-245页

作者： Xuanhan ZHOU Jun XIONG Haitao ZHAO Xiaoran LIU Baoquan REN Xiaochen ZHANG Jibo WEI Hao YIN college of electronic Science and technology National University of Defense Technology Systems Engineering Institute Academy of Military Sciences PLA

Unmanned aerial vehicles(UAVs) are recognized as effective means for delivering emergency communication services when terrestrial infrastructures are unavailable. This paper investigates a multiUAV-assisted communication system, where we jointly optimize UAVs’ trajectories, user association, and ground users(GUs)’ transmit power to maximize a defined fairness-weighted throughput metric. Owing to the dynamic nature of UAVs, this problem has to be solved in real time. However, the problem’s non-convex and combinatorial attributes pose challenges for conventional optimization-based algorithms, particularly in scenarios without central controllers. To address this issue, we propose a multi-agent deep reinforcement learning(MADRL) approach to provide distributed and online solutions. In contrast to previous MADRLbased methods considering only UAV agents, we model UAVs and GUs as heterogeneous agents sharing a common objective. Specifically, UAVs are tasked with optimizing their trajectories, while GUs are responsible for selecting a UAV for association and determining a transmit power level. To learn policies for these heterogeneous agents, we design a heterogeneous coordinated QMIX(HC-QMIX) algorithm to train local Q-networks in a centralized manner. With these well-trained local Q-networks, UAVs and GUs can make individual decisions based on their local observations. Extensive simulation results demonstrate that the proposed algorithm outperforms state-of-the-art benchmarks in terms of total throughput and system fairness.

关键词： unmanned aerial vehicle (UAV) trajectory design resource allocation multi-agent deep reinforcement learning (MADRL) heterogeneous agents

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Quantum Anomalous Hall Effect with Tunable Chern Numbers in High-Temperature 1T-PrN_(2) Monolayer

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Chinese Physics Letters 2024年第5期41卷 77-84页

作者：吴绪才李树宗司君山黄博张卫兵 Hunan Provincial Key Laboratory of Flexible electronic materials Genome Engineering School of Physics and Electronic SciencesChangsha University of Science and TechnologyChangsha 410114China

Quantum anomalous Hall(QAH) insulators have highly potential applications in spintronic device. However,available candidates with tunable Chern numbers and high working temperature are quite rare. Here, we predict a 1T-PrN_(2) monolayer as a stable QAH insulator with high magnetic transition temperature of above 600 K and tunable high Chern numbers of C = ±3 from first-principles calculations. Without spin-orbit coupling(SOC),the 1T-PrN_(2) monolayer is predicted to be a p-state Dirac half metal with high Fermi velocity. Rich topological phases depending on magnetization directions can be found when the SOC is considered. The QAH effect with periodical changes of Chern number(±1) can be produced when the magnetic moment breaks all twofold rotational symmetries in the xy plane. The critical state can be identified as Weyl half semimetals. When the magnetization direction is parallel to the z-axis, the system exhibits high Chern number QAH effect with C = ±3.Our work provides a new material for exploring novel QAH effect and developing high-performance topological devices.

关键词： magnetization topological monolayer

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Investigation of reflection anisotropy induced by micropipe defects on the surface of a 4H-SiC single crystal using scanning anisotropy microscopy

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Chinese Physics B 2024年第3期33卷 630-637页

作者：黄威俞金玲刘雨彭燕王利军梁平陈堂胜徐现刚刘峰奇陈涌海 Key Laboratory of Semiconductor materials Science Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China college of materials Science and opto-electronic technology University of Chinese Academy of SciencesBeijing 100049China National Key Laboratory of Solid-state Microwave Devices and Circuits Nanjing Electronic Devices InstituteNanjing 210016China Institute of Micro/Nano Devices and Solar Cells School of Physics and Information EngineeringFuzhou UniversityFuzhou 350108China State Key Laboratory of Crystal materials Shandong UniversityJinan 250100China

Optical reflection anisotropy microscopy mappings of micropipe defects on the surface of a 4H-SiC single crystal are studied by the scanning anisotropy microscopy(SAM)system.The reflection anisotropy(RA)image with a'butterfly pattern'is obtained around the micropipes by SAM.The RA image of the edge dislocations is theoretically simulated based on dislocation theory and the photoelastic principle.By comparing with the Raman spectrum,it is verified that the micropipes consist of edge dislocations.The different patterns of the RA images are due to the different orientations of the Burgers vectors.Besides,the strain distribution of the micropipes is also deduced.One can identify the dislocation type,the direction of the Burgers vector and the optical anisotropy from the RA image by using SAM.Therefore,SAM is an ideal tool to measure the optical anisotropy induced by the strain field around a defect.

关键词： scanning anisotropy microscopy SiC reflection anisotropy edge dislocation

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Effects of combustion temperature on the optical properties of brown carbon from biomass burning

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Journal of Environmental sciences 2024年第3期137卷 302-309页

作者： Peng Gao Rule Deng Song Jia Yue Li Xuefei Wang Qian Xing School of Chemistry sciences University of Chinese Academy of SciencesBeijing 100049China college of Chemistry and materials Engineering Beijing Technology and Business UniversityBeijing 100048China

Biomass burning has been known as one of main sources of Brown Carbon(BrC)in atmosphere.In this study,by controlling the combustion temperature at 250℃,350℃,and 450℃,the methanol soluble organic carbon(MSOC)and methanol insoluble carbon(MISC)from pine wood burning was collected by impinger.UV–Vis,excitation emission matrix(EEM),TEM and FTIR spectra were applied to investigate the properties of BrC collected.For MSOC at 250℃ and 350℃,all the spectral profiles of UV–Vis absorption and excitation emission matrix are almost the same,while the EEM of MSOC at 450℃ are different from that of the other two.For MISC fuorescence was observed only in the case of 450℃.In the FTIR spectra,with the temperature increasing the peaks associated to the oxygen-contained functions was weakened,indicating the formation of the fuorophores with larger conjugated system,especially aromatic hydrocarbons.Our results show that biomass combustion at low temperature produces more oxygen-riched BrC,which possesses relatively lower light absorption,while at high temperature produces more aromatics hydrocarbons with relatively strong light absorption.The results of this work are helpful to trace the source of brown carbon and optimize biomass energy utilization.

关键词： Biomass burning Combustion temperature Methanol-soluble brown carbon EEM Impinger

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