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WAVELET METHOD FOR CALCULATING THE defect stateS OF TWO-DIMENSIONAL PHONONIC CRYSTALS

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Acta Mechanica Solida Sinica 2008年第2期21卷 104-109页

作者： Zhizhong Yah Yuesheng Wang Chuanzeng Zhang Institute of Engineering Mechanics Beijing Jiaotong University Beijing 100044 China Department of Civil Engineering University of Siegen D-57076 Siegen Germany

Based on the variational theory, a wavelet-based numerical method is developed to calculate the defect states of acoustic waves in two-dimensional phononic crystals with point and line defects. The supercell technique is applied. By expanding the displacement field and the material constants （mass density and elastic stiffness） in periodic wavelets, the explicit formulations of an eigenvalue problem for the plane harmonic bulk waves in such a phononic structure are derived. The point and line defect states in solid-liquid and solid-solid systems are calculated. Comparisons of the present results with those measured experimentally or those from the plane wave expansion method show that the present method can yield accurate results with faster convergence and less computing time.

关键词： acoustic wave phononic crystal defect state wavelet band structure

Influence of defect states on band gaps in the two-dimensional phononic crystal of 4340 steel in an epoxy

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Chinese Physics B 2012年第9期21卷 400-403页

作者：孔肖燕岳蕾蕾陈雨刘应开 Institute of Physics and Electronic Information Yunnan Normal University

The band structures of a new two-dimensional triangle-shaped array geometry of 4340 steel cylinders of square cross section in an epoxy resin were studied by the plane-wave expansion and supercell calculation method. The band gaps of this type of phononic crystals with different defects were calculated such as defect-free, 60° crystal linear defect states, 120° crystal linear defect states, and 180° crystal linear defect states. It was found that the band gap will emerge in different linear defects of the phononic crystals and the bandwidth of linear defect states is larger than that of the free-defect crystal by about 2.14 times within the filling fraction F = 0.1-0.85. In addition, the influence of the filling fraction on the relative width of the minimum band gap is discussed.

关键词： defect state band width number of band gap

High transparency Pr:Y_(2)O_(3) ceramics:A promising gain medium for red emission solid-state lasers

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Journal of Advanced Ceramics 2022年第6期11卷 874-881页

作者： Qing LI Ying WANG Jun WANG Jie MA Meng NI Hui LIN Jian ZHANG Peng LIU Xiaodong XU Dingyuan TANG Jiangsu Key Laboratory of Advanced Laser Materials and Devices School of Physics and Electronic EngineeringJiangsu Normal UniversityXuzhou 221116China School of Electrical and Electronic Engineering Nanyang Technological UniversitySingapore 639798Singapore Engineering Research Center of Optical Instrument and System Ministry of Education and Shanghai Key Lab of Modern Optical SystemUniversity of Shanghai for Science and TechnologyShanghai 200093China Shanghai Institute of Ceramics Chinese Academy of SciencesShanghai 201899China

Highly transparent 0.5 and 1.0 at%Pr-doped Y_(2)O_(3)ceramics were fabricated by vacuum sintering plus hot isostatic pressing(HIP)*** selection of suitable pre-sintering temperatures and right microstructures before HIP was critical to obtain high density of the final sintered *** well-densified ceramics had pore-free microstructures with an average grain size of about 1μ*** was also found that the charge states of the Pr ions could be changed through regulating the annealing atmospheres,resulting in different absorption and emission characteristics in the visible wavelength *** in reducing atmosphere(5%H_(2)/95%Ar)favored the formation of Pr^(3+),resulting in stronger red emissions,while annealing in oxygen atmosphere led to the rise of lattice constant due to the concentration increase of oxygen *** H_(2)/Ar-annealed 0.5 at%Pr:Y_(2)O_(3)ceramics exhibited strong red emission at 600–675 nm,which may be a promising gain material for red solid-state lasers.

关键词： praseodymium ions(Pr3+) Y_(2)O_(3)ceramic valence state defect state optical properties

Theoretical Study on the Structural and Electronic Properties of the Reduced SnO_2 (110) Surface

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Chinese Journal of Structural Chemistry 2007年第5期26卷 606-612页

作者： ZHANG Yong-Fan LIN Wei WANG Qi-Wei LI Yi LI Jun-Qian Department of Chemistry Fuzhou University Fuzhou Fujian 350002 China state Key Laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter The Chinese Academy of Sciences Fuzhou Fujian 350002 China

The reduced SnO2（110） surface has been investigated by using first-principles method with a slab model. By examining the vacancy formation energy of three kinds of reduced SnO2（110） surfaces, the most energetically favorable defect surface is confirmed to be the surface with the coexistence of bridging and in-plane oxygen vacancies, which is different with the traditional model by only removing bridging oxygen. The results of band structure calculations indicate that the electronic structure of this defect surface is similar to the SnO surface.

关键词： SnO2(110) surface band structure defect state

Identification and elimination of inductively coupled plasma-induced defects in Al_xGa_(1-x)N/GaN heterostructures

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Chinese Physics B 2011年第7期20卷 393-398页

作者：林芳沈波卢励吾刘新宇魏珂许福军王彦马楠黄俊 state Key Laboratory of Artificial Microstructures and Mesoscopic Physics School of PhysicsPeking University Institute of Microelectronics Chinese Academy of Sciences

By using temperature-dependent Hall, variable-frequency capacitance-voltage and cathodoluminescence （CL） measurements, the identification of inductively coupled plasma （ICP）-induced defect states around the AlxGa1-xN/GaN heterointerface and their elimination by subsequent annealing in AlxGa1-xN/GaN heterostructures are systematically investigated. The energy levels of interface states with activation energies in a range from 0.211 to 0.253 eV below the conduction band of GaN are observed. The interface state density after the ICP-etching process is as high as 2.75× 10^12 cm^-***^-1. The ICP-induced interface states could be reduced by two orders of magnitude by subsequent annealing in N2 ambient. The CL studies indicate that the ICP-induced defects should be Ga-vacancy related.

关键词： inductively coupled plasma subsequent annealing defect state

Improved luminescence and photocatalytic properties of Sm^(3+)-doped ZnO nanoparticles via modified sol-gel route:A unified experimental and DFT+U approach

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Journal of Rare Earths 2023年第4期41卷 550-560页

作者： Sikder Ashikuzzaman Ayon Sajjad Hasan Md Muktadir Billah Sadiq Shahriyar Nishat Alamgir Kabir Department of Materials and Metallurgical Engineering Bangladesh University of Engineering and TechnologyDhaka1000Bangladesh Department of Physics Bangladesh University of Engineering and TechnologyDhaka1000Bangladesh Department of Materials Science&Engineering Rensselaer Polytechnic Institute(RPI)NY12180USA Department of Physics University of DhakaDhaka1000Bangladesh

In the current study,a modified sol-gel route was used to produce undoped and Sm^(3+)doped(1 mol%,3 mol%and 5 mol%)ZnO nanoparticles(NPs).The study of opto-structural properties of Sm^(3+)doped NPs was carried out both experimentally and *** dissolution of Sm^(3+)ions into the ZnO lattice is obviously seen from X-ray diffraction(XRD)*** evolution with doping was studied using field emission scanning electron microscopy(FESEM)and transmission electron microscopy(TEM).X-ray photoelectron spectroscopy(XPS)was carried out to confirm the prese nce of Sm~(3+)on the doped *** dopant quantity results in a redshift of the NPs along with a reduction in bandgap with increasing abso rption in the visible range,and a minimum of 3.18 eV of optical bandgap for Zn_(0.97)Sm_(0.03)O is *** spectroscopy reveals a drop in the recombination rate of electron-hole with increasing doping content till 3 mol%,followed by an increase of Zn_(0.95)Sm_(0.05)*** electron-hole pair recombination is revealed by the orange band in the luminescence *** analysis was also carried out with density functional theory(DFT).This work also unfolds the fundamental understanding of the structural properties of the synthesized NPs to enhance photocatalytic activity ***,photocatalytic activity for the optimum composition,i.e.,3 mol%,was assessed experimentally.

关键词： Samarium XPS Recombination rate Photocatalytic First principle defect state

Effects on the emission discrepancy between two-dimensional Sn-based and Pb-based perovskites

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Chinese Optics Letters 2022年第2期20卷 118-124页

作者： Tianju Zhang Chaocheng Zhou Jia Lin Jun Wang Laboratory of Micro-Nano Optoelectronic Materials and Devices Shanghai Institute of Optics and Fine MechanicsChinese Academy of SciencesShanghai 201800China Center of Materials Science and Optoelectronic Engineering University of Chinese Academy of SciencesBeijing 100049China Department of Physics Shanghai Key Laboratory of Materials Protection and Advanced Materials in Electric PowerShanghai University of Electric PowerShanghai 200090China state Key Laboratory of Advanced Optical Communication Systems and Networks School of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240China CAS Center for Excellence in Ultra-Intense Laser Science Shanghai 201800China

Two-dimensional (2D) Sn-based perovskites are a kind of non-toxic environment-friendly emission material with low photoluminescence quantum yields (PLQYs) and enhanced emission linewidths compared to that of 2D Pb-based ***,there is no work systematically elucidating the reasons for the differences in the emission *** fabricate (BA)_(2)SnI_(4)and (BA)_(2)PbI_(4)having different defect densities and different exciton-phonon scattering *** also reveal that 2D Sn-based perovskites have stronger exciton-phonon scattering intensity and higher defects density,significantly broadening the emission linewidth and accelerating the exciton relaxation process,which significantly reduces the PLQY of 2D Sn-based perovskites.

关键词： temperature-dependent photoluminescence spectra transient absorption spectra defect state exciton-phonon scattering two-dimensional perovskites

First principle study of nitrogen vacancy in aluminium nitride

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Chinese Physics B 2007年第12期16卷 3803-3808页

作者：耶红刚陈光德竹有章吕惠民 Department of Applied Physics Xi'an Jiaotong University Xi'an 710049 China

In the framework of density functional theory, using the plane-wave pseudopotential method, the nitrogen vacancy （VN） in both wurtzite and zinc-blende AlN is studied by the supercell approach. The atom configuration, density of states, and formation energies of various charge states are calculated. Two defect states are introduced by the defect, which are a doubly occupied single state above the valance band maximum （VBM） and a singly occupied triple state below the conduction band minimum （CBM） for wurtzite AlN and above the CBM for zinc-blende AlN. So VN acts as a deep donor in wurtzite AlN and a shallow donor in zinc-blende AlN. A thermodynamic transition level E（3＋/＋） with very low formation energy appears at 0.7 and 0,6eV above the VBM in wurtzite and zinc-blende structure respectively, which may have a wide shift to the low energy side if atoms surrounding the defect are not fully relaxed. Several other transition levels appear in the upper part of the bandgap. The number of these levels decreases with the structure relaxation. However, these levels are unimportant to AlN properties because of their high formation energy.

关键词： aluminium nitride density of states defect state formation energy

PLE spectra analysis of the sub-structure in the absorption spectra of CdSeS quantum dots

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Chinese Physics B 2006年第5期15卷 1067-1070页

作者：刘炳灿潘学琴田强吴正龙 The Department of Fundamental Courses The Academy of Armored Force Engineering Beijing 100072 China Department of Physics Beijing Normal University Beijing 100875 China Analytical and Testing Center Beijing Normal University Beijing 100875 China

The semiconductor CdSeS quantum dots （QDs） embedded in glass are analysed by means of absorption spectra, photoluminescence （PL） spectra and photoluminescence excitation （PLE） spectra. The peaks of absorption spectra shift to lower energies with the size of QD increasing, which obviously shows a quantum-size effect. Using the PLE spectra, the physical origin of the lowest absorption peak is analysed. In PLE spectra, the lowest absorption peak can be deconvoluted into two peaks that stem from the transitions of 1S3/2-1Se and 2S3/2-1Se respectively. The measured energy difference between the two peaks is found to decrease with the size of QD increasing, which agrees well with the theoretical calculation for the two transitions. The luminescence peak of defect states is also analysed by PLE spectra. Two transitions are present in the PLE, which indicates that the transitions of 1S3/2 1Se and 2S3/2 1Se are responsible for the defect states luminescence.

关键词： CdSeS PL spectra PLE spectra defect state