最新刊期
卷 24 ， 期 1 ， 2003
- 摘要：The phonon, quantized lattice vibration, plays a fundamental role in condensed matter physics. Professor Kun Huang is known throughout the world for his many pioneering contributions to physics, in particular to the phonon physics, a branch closely related to the luminescence in solids. His book entitled "Lattice Dynamics in Crystal Lattice"(in collaboration with Nobel laureate M. Born)is the first comprehensive and compact presentation in this field on the basis of quantum mechanics, which, although published about half century ago, is still used as standard textbook until now. In his early articles on the interaction between radiation field and ionic crystals, he first proposed an important idea later known as "polariton", which has changed our way of thinking about the propagating the EM Modes in crystalline media. His theory on multiphonon transition in semiconductors and insulators, the Huang-Rhys theory, which dealt with both the multiphonon optical and non-radiative transitions, laid the foundation of this important field. He pointed out the possibility of observing X-ray diffuse scattering in crystals due to impurities at first, later known as "Huang's diffuse scattering". In early 1950's, he formulated a pair of phenomenological equations relating the long-wavelength optical vibration to macroscopic electric field and polarization, which has been widely applied and named as Huang's Equation. As a 70 years old man, he and his collaborator resolved a puzzle about the optical phonon modes in semiconductor superlattices and worked out the "Huang-Zhu Model". In recognition of his lifetime achievements, Huang was recently honored with the Supreme Scientific and Technological Award in China. Huang's main scientific contributions and their significance are briefly reviewed in this paper.关键词：phonon physics;multi-phonon transition;Porariton;X-ray diffuse scattering;Huang's equation103|407|0更新时间：2020-08-11
- 摘要：The Langmuir-Blodgett(LB)technique is a way of preparing supramolecular organic thin films, which possess high order, uniformity, super thinness and a accurate control of film thickness, it is also harmless to substrates. Therefore, the films have shown considerable promise in frontiers of high technology research. In fact, the special functional systems can be assembled by LB technique on the basis of requirement molecular structures and the molecular packing and aligment are realized. The structure of the films as well as its physical properties are investigated and controlled at molecular level. At present, the LB films with specific functions have been successfully obtained such as monomolecular ultra thin insulating film, semiconducting film, conducting film and biological film, etc. In the early part studies of LB film were focused on the topochemistry. Since 1980's LB film technique is developed rapidly, it has been incorporatied with the research fields of condense state physics, material science, synthesis chemistry, microelectronic, biology and induced significant interest of scientists. The people desires to make novel sensitive mole electronic devices, optical non-linear devices, solar battery, optical switches of the information stores, bio-sensors, etc. We introduce mainly the history and preparation of LB films and research work of our group in over past ten years in this paper. The research results are described as follows. Firstly, we synthesized the substituted silicon phthalocyanine prepared, LB films, and obtained potential use in electronic device for the first time, and also reported the luminance diode with Au/LB film/ZnSe. Secondly, we have made great progresses in the synthesis of gas-sensitive materials and preparation of the films, and gas sensitive elements. We have synthesized firstly asymmetric and symmetric substituted copper phthslocyanine derivatives, and substituted phthalocyaninato-polysiloxane, the above materials were prepared for the gas-sensors used in detection of NH3. The sensitivity to NH3 is 1×10-7 and it reached the world levels of similar devices. Thirdly, we also studied on optical bistability of an optical waveguide coated with nonlinear Langmuir-Blodgett films by a prism coupling technique for the first time. The obtained threshold power densities of bistabilities were estimated to be 20MW/cm2, 32MW/cm2 and 40MW/cm2, respectively. The switching time is approximately 24ps. Fourthly, LB technique was applied in the biosensors and colorimetric transition process of polydiacetylene mannoside derivative LB films by binding Escherichia(E.coli)was investigated via UV-visible absorption spectra. The interfacial behaviors of the mixture at the air/water exhibited a good miscibility. In addition, we have analyzed the dynamical process of colorimetric transition caused by binding the E.coli to the mannoside derivative for the first time. It was estimated that one E.coli could only bind two mannoside molecules. We also describe a new method for using supramolecular assemblies composed of polydiacetylene supported on a electrode, which can provide easy and direct detection of bacteria through electrochemical technology. It utilizes an open platform to host biosensory elements allowing fast recognition and binding with the target molecules.关键词：Langmuir-Blodgett film;biosensor;mole-electronic device111|211|1更新时间：2020-08-11
- 摘要：We review the history of the long-lasting phosphorescent(LLP)materials and present its recent progress in this article. Some questions of the LLP materials, such as its phosphorescent mechanism, are also discussed. Basing on the principle of the abnormal-valence chemistry of lanthanide, we summarize the action of rare earth ions in LLP materials and present our idea on the designing of LLP materials. At last, we give our opinion on the probable development of LLP materials in future.关键词：long-lasting phosphorescent materials;rare earth ions;abnormal-valence chemistry323|484|32更新时间：2020-08-11
- 摘要：The properties of the exciton in the surface layer of crystals influence the properties of crystals very remarkably. In recent years,a lot of authors studied the surface polaron and the surface exciton. The properties of the exciton have been studied by many theoretical method by many investigators.Sumi et al. studied self-trapping of excitons(or electrons)interacting with phonons via short-range potential and found that the self-trapping depends strongly on the degree of lattice freedom.Chen et al. calculated the ground state energy of the strongly bound exciton-phonon system by using a concise variational approach.The influence of the interaction between phonons of different wave vectors in the recoil process on the effective potential between electron and hole, the self-trapping energy, and the self-trapping condition of the exciton in polar crystals has been discussed by using a perturbation method by present authors.Using the nearest-neighbor tight-binding approximation Luban et al. calculated the lowest bound-state energy of the effective 1D electron Hamiltonian and the exciton binding energy is obtained.The results for the exciton binding energy are in very good agreement both with experiment and the results of other theoretical calculations.Kasapoglu et al. calculated the binding energy of the exciton in the symmetric and asymmetric quantum wells by using a variational approach.The third-order nonlinear optical absorptions in hyperbolic quantum wires are studied by Guo et al., with most emphasis devoted to the influence of excitons on the third-order nonlinear optical absorptions. The analytic form for the third-order nonlinear optical absorption coefficient of this system is derived by means of density matrix treatment.A variational calculation of the ground-state energy of neutral excitons and of positively and negatively charged excitons(trions)confined in a single-quantum well is presented by Riva et al. They studied the dependence of the correlation energy and of the binding energy on the well width and on the hole mass.By using the method of few-body physics, the binding energy spectra of the second bound state of a negatively charged exciton X - in a GaAs quantum dot with a parabolic confinement have been calculated as a function of the electron-hole mass ratio and of the dot radius by Xie. The properties of the exciton have been investigated by many methods. Many of these mainly concentrated attention on the weak-and intermediate-coupling cases and on the ground state energy. However, the exciton in strong-coupling polar crystals and the excited state energy of the exciton has not been studied so far. Recently we study the internal excited state of the weak-coupling surface magnetopolaron by means of Huybrechts's linear combination operator method. In this paper,the properties of internal excited state of the strong-coupling surface exciton in polar crystals are investigated by using the linear combination operator and the unitary transformation method and the excited state energy, the excitation energy and the mean number of phonon of the strong-coupling surface exciton are calculated. The results show that the self-energy of ground state and excited state, the excitation energy and the mean number of phonon of the strong-coupling surface exciton could be written as a series in αs-1,the first term being proportion to,the coupling constant αs for Wannier surface exciton.关键词：surface exciton;internal excited state;mean number of phonon128|204|0更新时间：2020-08-11
- 摘要：In the early 1970's Ibach has made low energy electron diffracting(LEED)experiments on ZnO and other semiconductor surfaces. The surface polaron in crystals have been of considerable interest. Sak and Evans studied theoretically the surface polaron in polar crystals. In the 1980's Gu et al. discussed the weak and intermediate coupling surface polaran in semi-infinite crystals.Gu et al. investigated further the strong coupling surface polaron.In fact, so far research of the surface polaron only was restricted to the calculation of ground state energy. Huybrechts studied the properties of the internal excited state of the optical polaron by using the linear combination operator method.Gifeisman et al. calculated the wave functions of first excited state using perturbation theory. The excited state energy of bound Frhlich polaron was evaluated using the Fock approximation of Matz and Burkey by Lepine.A new variational wave function to describe the ground state and the excited states of a bound polaron is proposed by Devreese. Using the effective-mass approximation and the variational method the ground-state and first-excited state energy of a polaron in a polar-crystal slab,due to the interactions of the electron with the BO and SO phonons,are calculated self-consistently by Lu and Li. Qin and Gu investigate temperature dependence of the electron self-energy in the polar-crystal slab using Green-function method. In calculation,they consider the effect of the excited states on the electron self-energy and find the ground-state energy be about 11% lower than that of bulk polaron. A variational calculation is performed by Sahoo to obtain the ground state and the first excited state of the Frhlich bipolaron in a multidimensional polar crystal. Chun et al.discussed the hydrogenic impurity binding energy of the ground and the excited state in a cylindrical quantum wire by using Landau and Pekar variational method. However,using a Huybrechts's method, the properties of internal excited state of the polaron has not been investigated so far. In this paper, the effective Hamiltonian, the vibration frequency and the excitation energy of strong coupling surface polaron are calculated by using the linear combination operator and unitary transformation methods. Two limiting cases of coordinate z are discussed. The results show that for strong-coupling surface polaron the excitation energy will increase with increasing the electron-phonon coupling constant αS(αL)and the vibrational frequency of phonon ωS(ωL).关键词：strong-coupling;surface polaron;excitation energy96|153|1更新时间：2020-08-11
- 摘要：The Kronig-Penney model is an idealized model for calculating the energy bands in crystalline solids with periodical potentials.The conventional formalism is based on effective mass approximation and Bastard's boundary condition. The paper presents a transfer matrix method by which we can deal with many problems about one dimensional finite superlattices.The wave functions at any two positions inside the superlattice are connected by a product of transfer matrixes.The sequence of the matrixes matches the arrangement of the barriers and wells.No matter how the size and the height of the barriers and wells change,we need only to modify the matrixes corresponding to the barrier and well.It's evident that this kind of manipulation is very convenient for computing.Thus this method in this paper can also be used for studying electronic transmission through the one dimensional finite superlattices with arbitrary arranged barriers and wells. Some questions for the one dimensional finite superlattices are studied by means of transfer matrix method.We calculate transmittance and wave function of the one dimensional finite superlattices with one defect layer and also calculate electronic eigenvalues and its eigenfunctions when electron is bound into the one dimensional finite superlattices. We have observed the sharply resonant transmission associated with one defect layer and obtained its localized wave function.We also get exact eigenvalues and its eigenfunctions in this way.It is found that the ground state wave function has no node,and the nth excited state wave function has n nodes.This is true for all finite superlattices with arbitrary arranged barriers and wells.The evanescent boundary condition outside the superlattices demands that the wave function adds a node when the eigenenergy increases from a lower level to a higher level.The eigenvalues and its eigenfunctions are important to understand the electronical and optical properties of the superlattices.关键词：superlattice;transfer matrix;transmittance;eigenfunction99|149|0更新时间：2020-08-11
- 摘要：An comprehensive understanding of the characteristics of the organic material tris-(8-hydroxyquinoline)aluminum(Alq3)is meaningful for organic light-emitting devices(OLEDs). Thin films of Alq3 are among the most efficient electroluminescent molecular films known to date. Alq3 samples were synthesized and purified. The purity of samples is up to 98.5%. The electronic and crystallographic structure of Alq3 has been studied. The results of a joint experimental investigation based on a combination of X-ray diffraction(XRD)spectrum, hydrogen nuclear magnetic resonance(NMR)spectrum, infrared absorption(IRA)spectrum, mass(MS)spectrum, X-ray emission(XRE)spectrum and fluorescence spectrum of Alq3 have been investigated. The analysis on NMR spectrum of Alq3 shows that the coordinate interaction between Al3+ and O ion is more intensive than that between Al3+ and N ion. Al3+ hasn't replaced H ion that suggests the Al-O bond is covalent but not ionic bond in Alq3 molecule. There are still H+ around O ion. Since there are six coordination bonds around Al3+, O and N ions are both have strong binding force with Al3+. Therefore Alq3 has two types of geometrical isomers, namely mer isomer and fac isomer. From the IRA spectrum of the Alq3, the broad characteristic peak at 3417cm-1 corresponding to OH- stretching vibration confirmed that the Al-O are coordinate not ionic bond. The prominent peaks which is the characteristic of the absorption vibration of the aromatic ring skeleton at 1588, 1550, 1467 and 1400cm-1 suggests that the conjugate action of aromatic rings in molecule is very strong and all electron orbit of quinolinic rings are π bonding hybridizations. The disagreement between IRA spectrum of Alq3 and HQ is excellent for indicating that there is a strong coordinate action which affect O bonding heavily between Al3+ and O ions. From the MS spectrum the ratio of charge/mass of Alq3 has been achieved. We prospect if a further cleavage occurred, a peaks of Alq+ after losing a ligand from Alq2+ should locate at m/e=171. However, the peak was not observed indicating that the state of Alq+ is difficult to exist. The IRE data shows that the Kα1,2 peaks have shifted comparing to Al due to the perturbation as the ligand gives to 2p electron of Al. The perturbation is related to coordination intensity. The shift of Kβ of Alq3 mainly resulted from the chemical environment variation around Al atomics. It also relate to binding intensity and coordination number. The intensity of Kβ is lower than that of Kα The wave length of Kβ is shorter than that of K α.The peak of Kβ shifted to lower energy(about 3.5eV)whereas the peak of Kα1,2 shifted to higher energy(0.3 and 1.6eV)comparing to Al. Surprisingly, a weak adjoint peak at 1537.5eV was observed. We ascribed it to the formation of the hybridization orbit among O2s, O2p, N2s, N2p and Al3p orbits. Fluorescence data confirmed the existence of a fluorescent species formed between Al ion and 8-hydroxyquinolinol.关键词：Alq3;structure;characterization103|306|4更新时间：2020-08-11
- 摘要：Three different ligands with bis (8-hydroxyquinoline) were prepared by nucleo-philic addition reaction between 5-formyl-8-hydroxyquinoline and three diamines (4,4′-phenylenediamine, 4,4′-biphenyl-diamine and 4,4′-diamina-diaphenyl sulfone). Then these ligands were coordinated with zinc ion to prepare three new polymeric bis (8-hydroxyquinoline schiff base) zinc complex. The chemical structure of ligands and complexes was characterized by infrared absorption spectroscopy, ultraviolet absorption spectroscopy and elemental analysis, the results indicated that it was just the object we wanted. The photoluminescent performance of these complexes were investigated by fluorescence, the results showed that strong fluorescent emission peaked between 425nm and 625nm when excited by the light of maximal excitation wavelength, the peaks are at 497, 499 and 499nm for complex Zn-DD8Q, Zn-PD8Q and Zn-DDS8Q respectively, which is between blue light and green light. The fluorescence intensity of complex Zn-DD8Q is stronger in comparison with complex Zn-PD8Q and Zn-DDS8Q, due to DD8Q has stronger conjugative effect. It means the fluorescence intensity is changed by chemical structure of complex. When conjugative effect bigger, the fluorescence stronger. In general, a kind of excellent EL material may be also a kind of eminent PL material. So, the research object of EL material can be extended from the excellent PL material. Hence, in this research work we study the material′s PL performance and make setout for the next research of EL materials.关键词：polymeric complex;8-hydroxy-quinoline;zinc;photoluminescence94|284|10更新时间：2020-08-11
- 摘要：Much effort has been devoted in recent years to quantify the optical properties of superficial biological tissue from spatially resolved reflectance measurement, as they can be used to infer important physiological information. Some examples include the noninvasive measurement of the concentration of chemotherapy drugs or exogenous chromophores used for photodynamic cancer treatment and the assessment of hemoglobin oxygenation in tissue. The diffusion approximation to the Boltzmann equation has become the current standard for making theoretical predictions of spatially resolved reflectance because of its higher mathematical tractability compared with the general transport equation. In this regime, the parameters of interest are the absorption(μα)and the effective isotropic transport scattering(μ′s)coefficients. To a first crude approximation, superficial tissue can be considered as a semi-infinite turbid medium. Diffuse reflectance models have been developed for that geometry. In reality, superficial tissue is a multi-layered structure with each component having a different μα and μ′s. Recovery of the complete spatial distribution of μα and μ′sis the goal of optical tomography, and it is an open question as to whether this can be accomplished with sufficient accuracy. In an attempt to mimic tissue structure more realistically than the semi-infinite medium model, an improved, yet still crude, two-layer turbid medium model of tissue structure can be utilized. In this model, a top-layer thickness of 1~10mm that includes the epidermis and the dermis lies on top of a semi-infinite homogeneous medium that could be fat or muscle. In this article, a solution of the diffusion equation for a two-layered turbid medium having a semi-infinite second layer is derived by using the Fourier transform. Naturally, the assumptions that are inherent in each model will be reflected in the accuracy of its predictions and, consequently, the accuracy of the optical properties that can be inferred from it. The comparisons of the reflectance in the steady-state showed that the derived solutions of the two-layer model are close to the results obtained from two-layer Monte Carlo simulations. Thus, for many applications the reflectance calculated with the derived solution is exact enough to replace the time-consuming Monte Carlo simulations. Nonlinear regressions of these solutions of the diffusion equation to reflectance data obtained from two-layer Monte Carlo simulations in the steady-state showed the absorption and the effective isotropic transport scattering coefficients of the two layers can, in principle, be obtained. It was also shown by fitting the solutions of the diffusion equation to results obtained from Monte Carlo data that the optical parameters are obtained with different accuracy.关键词：biological tissue;absorption coefficients;effective scattering coefficients;Monte Carol simulotion95|140|3更新时间：2020-08-11
- 摘要：ZnSe epilayers were grown on Si(111)substrates by low-pressure metalorganic chemical vapor deposition(MOCVD)with ZnO as a buffer layer. ZnO films were prepared by radio frequency(RF)magnetron sputter deposition technique. X-ray diffraction measurements showed that ZnSe film grown on ZnO-Si(111)substrates were epitaxial films with strong(111)preferential orientation. It is found from X-ray diffraction that the longer time annealing of ZnO films, the better crystallization of ZnSe films were. Photoluminescence(PL)showed that with the higher annealing temperature of ZnO buffer layer, the better ZnSe films also. The photoluminescence(PL)showed a strong and dominant peak emission at near-band-edge emission about 450nm,which was ascribed to free exciton emission. Above results indicated that quality of ZnSe films grown on Si(111)substrates were improved by using ZnO as a buffer layer.关键词：ZnSe film;Si-substrate;ZnO buffer layer;MOCVD98|156|0更新时间：2020-08-11
- 摘要：It was known that silicon nitride is a wide band-gap semiconductor emitting photoluminescence(PL)at low temperatures in the late eighties of 20th century .In this paper, silicon nitride film was prepared by low pressure chemical vapor deposition(LPCVD). The PL of the samples was measured at room temperature by an Nd:YAG laser spectrometer with excitation of 265nm(5.0eV).Under the laser excitation, six luminescence emission bands of LPCVD silicon nitride film were observed corresponding to photon energies of 2.97, 2.77, 2.55, 2.32, 2.10 and 1.9eV respectively. The result of X-ray photoelectron spectroscopy(XPS)shows that the N/Si ratio of the samples is 0.76. Reports on the relative gap state model of LPCVD silicon nitride film has been made previously by the same authors[4]. A series of LPCVD-Si3N4 films was treated by rapid thermal annealing(RTA)for 5s in N2 at 800, 900, 1000 and 1100℃. Another six PL peaks at 3.1, 3.0, 2.85, 2.6, 2.36 and 2.2eV were observed after RTA at 900~1100℃.The six peak positions of PL after RTA at 800℃ are much as the same as that of as-synthesized. The infrared spectra(IR)of samples annealed at 900~1100℃ show that the Si-O-Si bond-stretching bands are weaker than that for the samples as-synthesized or after RTA at 800℃. The 3.1, 3.0, 2.36 and 2.2eV emission bands of the annealed samples are caused by the electronic transition of ≡Si0→Ev, ≡Si0→N-Si-O,≡Si0→N- and Ec→≡Si0,respectively. These emission bands are higher than the energy gap of the as-synthesized samples. The two new emission bands of 2.85 and 2.6eV may be related to the oxygen-vacancies(≡Si0-Si0≡)in the annealed samples. Based on the results of X-ray diffraction, IR and XPS, we conclude that the amount of the oxygen-vacancies plays an important role in the photoluminescence at 2.85 and 2.6eV. The origin of these emission bands is discussed.关键词：low pressure chemical vapor deposition(LPCVD);silicon nitride film;rapid thermal annealing(RTA)108|193|0更新时间：2020-08-11
- 摘要：ZnO thin films with a strong c-axis orientation have been successfully deposited on Si substrate at room temperature(RT)by using JPGF-450 r. f. magnetron sputtering system. A sintered ceramic ZnO target with 99.99% purity was used as source material. A mixture of Ar(99.999%)and O2 (99.999%) were used as sputtering gases. The argon and oxygen were introduced via two separately controlled leak valves so that the partial pressure could be adjusted. During film deposition, the argon partial pressure maintained at 1Pa, and the oxygen partial pressure maintained at 0, 2 and 5.2Pa respectively for different samples. The sputtering r. f. power was 200W and sputtering time was 20 minutes. The ZnO films were grown with argon partial pressure of 1Pa and oxygen partial pressure of 0, 2 and 5.2Pa, respectively. The XRD spectra revealed that all samples were polycrystalline and had a preferred orientation with c-axis perpendicular to the substrates. All samples show typical luminescence behavior with a narrow 446nm(2.78eV)emission peak when excited with 300nm light. The intensity of the PL peaks is found to be strongly dependent on the oxygen pressure during films deposition. As the oxygen partial pressure increase, the PL intensity decreases quickly. The blue emission is also affected by annealing in different ambient. For the vacuum annealed sample, the intensity of PL increases markedly. On the contrary, for the samples annealed in oxygen, the PL intensity decreases. The experiments prove that the luminescence emission peak located at 446nm corresponds to the electron transition from the shallow level of oxygen vacancy to valence band.关键词：ZnO films;magnetron sputtering;photoluminescence104|123|13更新时间：2020-08-11
- 摘要：ZnO,a wide direct-gap semiconductor, attracts as much attention as GaN in optoelectronics research field. ZnO not only has the same crystal structure as GaN, but also has strong exciton binding energy of 60meV which is 2.4 times to that of GaN. ZnO films have been grown by many methods, such as chemical vapour deposition(CVD), molecular beam epitaxy(MBE)and metal organic chemical vapor deposition(MOCVD). We adopt sputtering for the growth of ZnO films. Sputtering methods have several advantages. They can deposit large area films of well controlled compositions economically and the growth rate is high enough for thick films and low enough for ultrathin films by changing the sputtering rate. ZnO films were deposited on(001)silicon substrate by radio frequency(r.f.)magnetron sputtering. Gas flux ratio of O2 to Ar and the RF power is 3:1 and 600W, respectively. The sputtering time was 40min. The substrates were rotated and heated to 200℃ during the sputtering. The X-ray diffraction(XRD)patterns of the sample showed sharp diffraction peak for ZnO(002),which indicate that as-sputtered film were highly c-axis oriented. The sample grown under the conditions could generate strong luminescence of ZnO. The band edge emission and deep level emission were observed in photoluminescence(PL)spectra at room temperature.关键词：ZnO thin film;RF magnetron sputtering;PL spectra97|144|5更新时间：2020-08-11
- 摘要：In high energy physics experiments, large arrays of scintillation crystals has been used in electromagnetic for precision measurements of photons and electrons. Lead tungstate is a fast and dense scintillating crystal and has been selected as scintillator for the construction of calorimeter in CMS experiment of Large Hadron Collider(LHC)at CERN(European Organization for Nuclear Research)this century. In the course of studying the effects of various heterovalent ions introduced into the PbWO4 lattice, we have found that Y3+ ions can significantly improve the optical transmittance in the short wavelength region. Correlated measurements of transmission, X-ray excited emission, positron annihilation lifetime and X-ray photoelectron spectrometers were performed on a selected set of undoped and Y-doped PbWO4 single crystals. The samples were grown from 5N purity raw powders by modified Bridgman method and show the blue emission component only. The transmittance, luminescence and point defects of Y doped PbWO4 crystal have been studied by these methods. The results show that Y dopants can improve the luminescence property of the crystal, i.e. it can increase the ratio of fast luminescent component, and suppress the concentrations of positron capture centers and low-valent oxygen ions. It was tentatively proposed that Y3+ dopants would mainly occupy the sites of lead vacancies resulted from Pb volatilization but not replace the lattice Pb2+ ions. This is the reason why the absorption edge of PbWO4:Y crystal slightly shifts to shorter wavelength. The low-valent oxygen ions suppression can lead to the decrease of green luminescence centers(WO3+O-)so as to result in higher ratio of fast luminescent component.关键词：Y doped PbWO4 crystal;point defects;positron annihilation lifetime;X-ray photoelectron spectrum124|99|2更新时间：2020-08-11
- 摘要：Series of niobate-phosphate and niobate-silicate glasses doped with Eu3+ ions were prepared. The emission, phonon-side band spectra and fluorescence lifetimes of these glasses were studied and the intensity parameters Ω2 of Eu3+ were obtained. The temperature-dependence of emission intensity of the Eu3+-ion in these niobate glasses was investigated. The temperature-quenching rates were determined. The results indicate that in niobate glasses, as the concentration of Nb2O5 increases, the covalence becomes strong, the symmetry becomes low and the electron-phonon coupling strength becomes strong, thus the lifetimes become short, the nonradiative transition processes and the temperature-quenching become strong. The temperature-dependent behavior of the Eu3+ ion was studied in various niobate glasses. The variation of the emission intensity of Eu3+ with temperature was attributed to two factors, the thermally excited emission from 7F2 to 5D2 and the temperature-quenching effect. The former tends to cause the intensity of Eu3+ increase with temperature, while the later tends to cause the intensity decrease. The temperature-quenching rates in various glasses were obtained. They increase with the increasing concentration of Nb2O5. The temperature-dependencies of the peak energies and the line widths of 5D0→7FJ(J=0,1)were experimentally determined.关键词：Eu3+ doped niobate glasses;intensity parameters;phonon-side band spectra;electron-phonon coupling;thermal population;temperature-quenching125|129|4更新时间：2020-08-11
- 摘要：In recent years, vacuum ultraviolet(VUV)optical properties have become of special importance for luminescent materials. The main interest has been in the development of new and efficient plasma phosphors to realize a gas discharge color picture display panel and mercury-free fluorescent lamps. Plasma phosphors are required to have high conversion efficiency under VUV excitation. Therefore, the strong absorption of phosphors in the VUV region is very important for the plasma phosphor. While compounds with aluminate groups have strong absorption in the VUV region. Thus VUV excitation spectra of BaMgAl10O17:R2+(R=Eu,Mn)were investigated. The starting materials were Al2O3(4N), MgO(A.R.), BaCO3(4N), En2O3(4N)and MnCO3(A.R.). They were thoroughly mixed in an agate mortar with a certain AlF3 as flux. The mixtures were introduced in an alumina crucible and heated for 2 hours at 1 450℃ in the presence of carbon. The VUV excitation spectra of the visible luminescence of BaMgAl10O17:Eu2+ is composed of two broad bands peaking at about 165 and 248nm. One band in the region from 200nm to 300nm is attributed to the absorption of the 4f→5d transition of Eu2+ ions. The other band in the region from 120nm to 200nm is due to the host absorption. This result indicates that there is an energy transfer from host to Eu2+ ions. Under 147nm excitation, the emission spectrum of Ba0.9Eu0.1MgAl10O17 consists of a broad band at about 448nm, corresponding to the 4f→5d transition of Eu2+ ions. The VUV excitation spectrum of BaMg0.8Mn0.2Al10O17 consists of three broad bands in the range from 120nm to 240nm. The two bands located in the range from 120nm to 180nm are ascribed to the absorption of the host absorption. The band peaking at about 198nm is not attribute to the host absorption, it may be associated with the absorption of Mn2+. For a free ion of Mn2+,the energy separation between 6S(3d5)and 6D(3d44s)levels had known to be around 6.3×104cm-1. Therefore, it may be assigned to one of these 3d5→3d44s transitions. Under 147nm excitation, the emission spectrum is dominated by the green Mn2+-band at about 516nm. It is assigned to the transition from the lowest excited state to the ground state, i.e., 4T1(4G)→6A1(6S). The green emission of Mn2+ indicates that Mn2+ ions occupy the sites of Al3+ which have tetrahedral coordination.关键词：BaMgAl10O17;Eu2+;Mn2+;VUV excitation spectra120|109|3更新时间：2020-08-11
- 摘要：Field emission displays(FEDs)offer the potential of achieving comparable or superior levels of performance to the cathode ray tubes(CRTs). However, FEDs must operate at significantly lower excitation voltages(≤5kV)and higher current densities(10~100A/cm2)than that of CRTs. Thus the phosphors for FEDs are required to have a high efficiency at low voltages, high resistance saturation, long service time, and equal or better chromaticity than that of CRT phosphors. For full color flat panel displays, vary satisfactory red and green commercial phosphors are being produced by the f→f transitions of Tb3+ and Eu3+, but suitable blue phosphors are still lacking, because wide band gap materials are required and the eye sensitivity is quite low in the blue spectra region. Sr2CeO4 is an efficient blue phosphor found by combinatorial method and prepared by the decomposition of carbonates, acetates and oxalates. But these methods always were realized at temperatures above 1000℃ for a period as long as 48h. The sol-gel method, because of its apparent advantages of fine homogeneity, high reactivity of starting materials and lower sintering temperature, is a new route to synthesize fine powders. It has attracted more and more attention. The method was widely used to prepare multicomponent oxides, such as superconductors etc. In this paper, Sr2CeO4 phosphors were prepared by a Pechini sol-gel method via inorganic precursors Sr(NO3)2 and Ce(NO3)3 together with organic chelating agent citric acid and cross-linking agent polyethylene glycol(PEG). X-ray diffraction(XRD), scanning electron microscope(SEM), and photoluminescence spectra were used to characterize the Sr2CeO4 phosphors. The results of XRD show that the crystallization of Sr2CeO4 begins at about 800℃, completes around 900℃ with a triclinic structure. SEM studies show that the 900℃ annealed samples are well crystallized, with grain size range from 1μm to 5μm. The excitation spectrum of Sr2CeO4 phosphor displays a broad double peaks band with one around 310nm and the other around 340nm. This broad band is due to the charge transfer(CT)band of the Ce4+ ion. Excited with a radiation of 340nm, a broad emission band is observed with a peak position at 475nm, and the full width at half maximum(FWHM)of 93nm,the band can be assigned to the f→t1g transition of Ce4+. The emission spectrum of Sr2CeO4 excited with 310nm radiation is similar to that excited with 340nm radiation.关键词：Pechini sol-gel;luminescence;Sr2CeO4107|89|14更新时间：2020-08-11
- 摘要：SrAl2O4:Eu, Dy is a new kind of attractive long-persistent luminescent material with green afterglow. It is necessary to make clear the mechanism of long-persistent luminescence of SrAl2O4:Eu,Dy. This paper was to investigate the effect of powder size on the luminescence of the material. In this work,SrAl2O4:Eu,Dy were made by heating at 1 350℃ for 5 hours in a reducing atmosphere of carbon powders.Then the blocks of SrAl2O4:Eu,Dy were milled into powders and separated by sieves with mesh numbers of 100,200,300,400 and 500,respectively. Also the powders sieved with 500 mesh were further separated by alcohol floatation method. Some white powders with very fine size can be removed from the green powders by alcohol floatation. It was found that the luminescent strength of the powders would decrease when their size become smaller. Among these powders the one separated by 100 mesh sieve has the strongest luminescence. The luminescence of the fine white powders separated by alcohol floatation is very poor,and the rest of the green powders will have better luminescence than that without alcohol floatation. The emission peak position in emission spectrum will not move due to powders size,but the excitation peak position in the excitation spectrum moved towards to short wave length when the powders become smaller. SEM and EDS experiments were carried out to study the size and chemical component of the powders. The white powders have a size of 1~2μm and the green powders have a size of about 20μm after alcohol floatation. In the green powders,Eu component is equal to or more than Dy component. However,in the white powders,Eu component is less than Dy component. It is reasonable to consider that too much Dy caused the luminescence decrease in the white powders.关键词：luminescence;SrAl2O4:Eu;Dy;granularity100|108|5更新时间：2020-08-11
- 摘要：The reliability of coated and uncoated mirror facets InGaAs/GaAs and InGaAsP/GaAs high- power semiconductor lasers has been studied through aging experiment. The threshold current and output light power of the lasers were tested before aging, and it showed that the threshold current of the lasers with coated facets is decreased by a factor of 4 than that of lasers with uncoated facets. Then both kinds of lasers were tested after aging at 1.2 times of the threshold current for 40h.It showed that the threshold current was increased by more than 25mA, and output light power decreased more than 50% compared to those of without aging. So to lenghtened the lifetime of lasers, it is important that the mirrors facets must be coated.关键词：laser;coated or uncoated facet;aging98|119|0更新时间：2020-08-11
- 摘要：From the viewpoint of application electroluminescence(EL)is especially useful in the technology of flat panel display(FPD). Among the six types of emission FPDs,inorganic electroluminesence(IEL)and organic electroluminescence(OEL)are especially promising because of their several attractive characteristics.But there are still some deficiencies in their behavior.The main problem is the lack of blue colored emission in inorganic EL and the lack of electron transport materials and stability in organic EL.But because of the compansatory properties of IEL and OEL, it is quite natural to develop their superiority and to minimize their inferiority.From this analysis,we are convinced that the heterogeneous junction made from organic and inorganic materials as well as the excitation with AC and DC sources may satisfy the above-metioned requirements.In inorganic EL layered optimization has been proposed and investigated carefully.The aim of that structure is to strengthen the effect of electron acceleration in phosphors by spatially separated addition of pure electron acceleration layer to the ordinary IEL layer.But in reality the energy of electrons before entering phosphor layer have already enough value to excite centers of luminescence in the visible region by direct impact excitation.Since these energetic electrons are accelerated not in vacuum but in solids,the luminescence generated by their bombardment is called Solid State CL or CL-like emission.Since ZnS is well known in EL and has also good ability to accelerate electrons,so that in this paper,we prepared the organic/inorganic heterojunction of MEH-PPV under AC electric field excitation which is similar to the photoluminescence of MEH-PPV.By studying the optical characteristics of the device,we found that the emission was induced by direct bombardment of the accelerated electrons from ZnS.So it comes from the solid state cathodoluminescence.关键词：solid state cathodoluminescence;organic/inorganic heterojunction;polymer electroluminescence104|128|1更新时间：2020-08-11
- 摘要：Recently, solid state white lighting, optical data storage and biochemical identification applications have led to a tremendous surge in research aimed at developing high power violet and ultraviolet light emitting diodes(V-LEDs and UV-LEDs). The white LEDs have come to be expected for use in lighting, which consists of a blue LEDs and yellow phosphor or an violet(or UV)LED and red-green-blue phosphors, but conversion efficiency and chromaticity of white LED with violet(or UV)LED were better than that with blue LEDs. Although high-brightness blue LEDs have been realized, high-power violet(or UV)LEDs have not yet been realized due to the high dislocation density. One possible reason for this is considered as the suppression of non-radiative recombination center in In xGa 1-xN active layers. It is known for violet(or UV)LEDs that the addition of a small amount of In to GaN active layer results in the improvement of emission wavelength and efficiency. Recently, the epitaxial lateral overgrowth(ELOG)is effective in reducing the dislocation density, so it can be used to fabricate high-power violet(or UV)LED. Violet-LEDs with InGaN/GaN multi-quantum-wells(MQW)structure were grown by low-pressure metalorganic vapor phase epitaxy(LP-MOVPE). The double crystal X-ray diffraction revealed distinct second order satellite peaks. The emitting peak of PL spectra is at 399.5nm with FWHM of about 15.5nm. InGaN/GaN MQW violet-LEDs have been successfully fabricated with forward voltage about 4V at 20mA injection current.关键词：InGaN;quantum well;violet LED;MOCVD92|95|2更新时间：2020-08-11
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