最新刊期
卷 24 ， 期 4 ， 2003
- 摘要：Composite materials of rare earth metals and polymers are a series of functional materials with many excellent properties and potential application. This review presents the research state over the decades on the preparation of polymers containing rare earth metals in doping-type and bonding-type, and its applications on the fields of optics, electricity, magnetic, catalysis, analysis, etc. The rare earth compounds were uniformly dispersed into monomers and polymers as dopant in doping type rare earth polymer, while the bonding type rare earth polymers could be synthesized by the following three approaches:In the first approach, lanthanide ions were incorporated with the reactive functional groups such as hydroxyl and carboxyl in the polymer side chains; The second one is that lanthanide ions were coordinated with polymer dentate ligands such as β-diketonates, carboxyl, pyridine, porphyrin and sulfo group; The third one is homopolymerization and copolymerization of the monomers containing lanthanide ions. In addition, some research results in our groups on the synthesis and properties of optical resins containing rare earth compounds were summarized. In our recent work, some binary and ternary rare earth complexes were dispersed into the styrene/methylacrylic acid copolymerization system, and the optical resins possess a high transparency, intense luminescent properties and good mechanical properties were obtained.关键词：optical resin;rare earth;composite materials89|128|2更新时间：2020-08-11
- 摘要：ZnO thin films doped with NH3 have been grown on R-plane sapphire substrate by MOCVD and the growth parameters have been optimized by XRD and SEM method. The only 〈1120〉oriented ZnO thin film has been obtained in 610℃ and 80sccm NH3 flux, and the FWHM of 〈1120〉 plane X-ray diffraction peak is only 0.50°. At the same time, the samples’SEM images show that the surface of the sample with 80sccm NH3 is the most smooth, which may be related to the amount of hydrogen atom in the sample. The electronics properties of the samples were determined by Hall method. The results show that the resistivity of the film with 80sccm NH3 is up to 108Ω·cm, and the film with 50sccm NH3 shows low p-type. In order to investigate the nitrogen atom form in the samples, X-ray photoelectron spectra of the samples have been studied. The results show that the N1s photoelectron comes from N3- for the sample with 50sccm NH3. For the sample with 80sccm and 110sccm NH3, the N1s photoelectron comes from NH2- and NH2-, respectively. This implies that some hydrogen atoms were introduced into the samples with increase of NH3 flux. All above indicate that high quality ZnO thin film doped with NH3 has been obtained on R-plane sapphire substrate. Furthermore, some films show not only high resistivity but also low p-type, which is good for the application of ZnO film. 关键词：sapphire;ZnO thin film;MOCVD;XPS83|65|0更新时间：2020-08-11
- 摘要：Illuminated by ultraviolet light, the electrons in semiconductor transfer from valence band to conduction band with the absorption of photo energy, the formation of free electrons and hole carriers. The electrons in the processes of migration in the conduction band may be affected by different defect energy level, such as being captured by electron traps, recombination with luminescent centers, or recombination with the hole carrier in valence band. The investigation of the decay processes of photoelectrons in conduction band is helpful in achieving an understanding of the energy level structure for semiconductor materials. Contactless measurement of the decay processes of photoelectrons of microcrystal materials and powder semiconductor materials can be carried out using the microwave absorption dielectric spectrum detection technique, with high precision and low interference. ZnO crystals is a kind of semiconductor materials with a band with an energy gap of 3.37eV at room temperature. The ZnO experimental samples are prepared using hydrothermal synthesis method that is often used in preparation of high purity and fine dispersion ZnO crystals. The decay processes of photoelectrons of nano ZnO materials and ZnO microcrystal materials have been measured respectively in this paper by using microwave absorption method. The photoelectron time resolved spectrum of nano ZnO and ZnO microcrystals were obtained. The evidence difference of photoelectron lifetime between two kinds of materials was found after excitation with a short-pulse laser. The photoelectron lifetime of nano ZnO was found only to be 10ns and the photoelectron lifetime of ZnO microcrystals was found to be 50ns. It is believed that the photoelectron lifetime of nano ZnO is shorter than that of ZnO microcrystals because the surface area of nano material is larger than that of microcrystal materials. The defect energy levels on the surface area of nano materials also result in the increasing of recombination rate of the photoelectrons.关键词：ZnO;photoelectron;microwave absorption;decay process99|99|3更新时间：2020-08-11
- 摘要：ZnO has a large fundamental band gap of 3.37eV, which makes it a promising material for use in ultraviolet light-emitting devices and laser diodes. Apart from higher chemical and thermal stability, ZnO has the advantage of a large exciton binding energy(60meV), which assures more efficient excitonic emission at higher temperature. Up to now, the visible emission and ultraviolet lasing emission of ZnO have been the subject of much research. The properties of the excitonic luminescence for nanocrystalline ZnO thin films were investigated about the dependence of excitonic photoluminescence(PL) spectra on temperature. High quality nanocrystalline ZnO thin films were prepared by thermal oxidation of ZnS films prepared by low pressure metalorganic chemical vapor deposition(LP MOCVD) technique. The X-ray diffraction(XRD) indicates that the ZnO thin films have a polycrystalline hexagonal wurtzite structure with a preferred (002) orientation when ZnS thin films were oxidized at annealing temperature of 800℃ in an oxygen ambient and the average grain size for all films annealed at 800℃ is about 33nm. The properties of excitonic PL spectra for nanocrystalline ZnO thin films were investigated in the temperature range from 82K to 300K. The photoluminescence(PL) spectra of the ZnO thin films showed that the strong ultraviolet(UV) emission peak at 380nm, while the deep level emission band is barely observable at room temperature. The UV emission is assigned to free excitons and DL emission band is attributed to excitons bound to neutral acceptors. The strength of the exciton longitudinal optical(LO) phonon coupling is deduced from the temperature dependence of the FWHM of the fundamental excitonic peak, the reduce of the exciton longitudinal optical(LO) phonon coupling strength is due to the quantum confinement effect. Because of the quantum confinement effect for nanocrystalline ZnO thin films, the energy separation between 1s and the first excited state(2s) becomes large, and the dissociation efficiency of 1s exciton into the first excited state(2s) or other excited states of the continuum states is largely suppressed. The transition from the ground state(1s) to other excited states including 2s state is reduced and ГLO is effectively reduced.关键词：nanocrystalline ZnO thin film;excitonic luminescence;photoluminescence;thermal oxidation;LP-MOCVD85|101|3更新时间：2020-08-11
- 摘要：The mechanism behind the visible luminescence of ZnO is still a question of debate. To find out the mechanism,the emission properties of nanocrystalline ZnO colloids with different particle sizes were studied in the present paper. The preparation procedure of nanocrystalline ZnO colloids consists of two major steps:(1) preparation of precursor and (2) hydrolysis of the precursor to form the colloid. Zinc acetate and methanol were used to prepare the precursor without further purification,and NaOH was used to hydrolyze the precursor,respectively. The sizes of ZnO particles increase with the reaction time. The emission spectra were taken at different times during the growth of ZnO particles in methanol at room temperature. In this way one can study nanocrystalline ZnO particles with different sizes. Two emission bands were observed,one being an exciton emission and the other being visible emission. The energetic positions of the maxima of both emission bands depend on the size of the ZnO particles. We found that the two emission bands shift to lower energies positions upon particle growth. This is a quantum size effect and can be understood in terms of confinement of charge carriers. Contrary to the nanocrystalline ZnO powder,the emission intensities of the nanocrystalline ZnO colloids increases as the sizes of ZnO particles are decreased. Studies on the variation of the energetic positions of the maxima of both the UV and visible emission band of ZnO as a function of particle size provide novel information on the nature of the visible emission transition,which is valid for ZnO in general. The energetic positions of both band edges can be calculated as a function of particle size. A linear relationship between the maximum energetic positions of the two emission bands was given both from our experiments and from our calculation in this paper. Accordingly we attribute the visible emission to the transition of an electron from the conduction band to a deep trap.关键词：nanocrystalline ZnO colloids;visible emission;exciton emission;quantum size effect92|121|7更新时间：2020-08-11
- 摘要：In this paper many different shapes of ZnO crystals were synthesized by hydrothermal method when different mineralizer concentration and different temperature were used. When mineralizer concentration was less than 2mol/L KOH and the fill factor was approximately 35% at 350℃, only micro crystal ZnO was synthesized with size of several micron. When mineralizer concentration was more than 3mol/L KOH and the fill factor was approximately 35% at 350℃, many shapes of ZnO crystals were synthesized with many different size, the size of maximal crystal is from several decade micron to two hundred micron, the small size crystal is only several micron. When mineralizer concentration was respectively 4mol/L, 5mol/L KOH, no bigger ZnO crystals were synthesized. The complete faces of ZnO crystal are exposed when high mineralizer concentration is used at 350℃, they are hexagonal facesm{1010}, hexagonal cone faces p{0111}, negative polar faces {0001} and sometimes positive faces {0001}. Sometimes many holes are observed on the faces of ZnO crystals, which shows bad completeness of crystal. When temperature was at 430℃ and mineralizer concentration was 2mol/L KOH, the bigger ZnO crystals were synthesized, the size of maximal crystal is several hundred micron, the small size crystal is only several micron. When mixture of 2mol/L KOH and 1mol/L KBr was used as mineralizer at 430℃, the size of maximal crystal is 1mm. When mineralizer concentration was 4mol/L KOH the size of crystals doesn’t get bigger. The exposed faces of bigger crystal synthesized at 430℃ are hexagonal faces m {1010}, hexagonal cone faces p{1011}, negative polar faces {0001}, the shapes of crystal are hexagonal cone, the faces of ZnO crystals are smooth, complete and the quality of crystals is higher than that of crystals synthesized at 350℃.关键词：ZnO;hydrothermal synthesis;mineralizer;crystal shapes120|95|1更新时间：2020-08-11
- 摘要：The cyclotron resonance is a standard technology that determines the conductive electron and hole mass in solids. Usually the effective mass of electron is decided according to the cyclotron-resonance frequency confirmed by experiment. It should be noted that the split of cyclotron-resonance spectrum is strongly affected by the coupling of electron-phonon. Many scholars have paid much attention to the cyclotron resonance of polaron. Many investigations on the properties of the magnetopolaron were performed by means of Feynman’s route integration, Larsen’s original operator, Green function, linear combination operator, variation, bound Landau state and perturbation method. At investigating the properties of the crystals, many methods was only confined to the one LO phonon branch, however, in the polyatomic crystals containing three and more atoms, with several atoms per unit cell, there are more than one LO phonon. The polar problem of the crystals containing many LO slab has been investigated. In recent years, the polaron problem with many LO phonon branches has been investigated also. However, the magnetopolaron in polyatomic polar crystals has rarely been investigated. Recently Hu et al. discussed the properties of the surface magnetopolaron and bulk magnetopolaron in polyatomic polar crystals by means of a linear combination operator.But the properties of polaron of polyatomic crystals in magnetic field has not investigated so far. In this paper, the vibrational frequency and effective mass of the weak-coupling magnetopolaron in the polyatomic semi-infinite polar crystals were studied through a linear combination operator and unitary transformation and by using Lagrange’s multiplier. When the electron is approaching infinitely to the surface of crystals, the vibrational frequency and effective mass of the magnetopolaron is identical with the surface magnetopolaron. When the electron is situated in the depth of crystals, the vibrational frequency of the magnetopolaron is not changed, but effective mass of the magnetopolaron related to its depth as well as the coupling constant of LO-electron.关键词：polyatomic semi-infinite polar crystals;magnetopolaron;vibrational frequency;effective mass82|76|0更新时间：2020-08-11
- 摘要：With the development of the theory of the solid science and experimental technology,the research the properties of magnetopolaron in crystals has been of considerable interest.Peeters and Devreese studied the properties of magnetopolaron using a Feynman’s path integral method.Wei and co-workers studied the induced potential and the self-energy of an interface magentopolaron interacting with bulk LO phonons as well as interface optical phonons using the Green function method.Zorkani et al.calculated the ground state energy of bound magnetopolaron using variational method.If consider the interaction between phonons of different wave vectors in the recoil process,the magnetic field dependence of cyclotron resonance frequency,induced potential,the effective interaction potential,and the cyclotron-resonance mass of the surface magnetopolaron is obtained by using a linear combination operator and perturbation method by one of the authors.The magnetic field and temperature dependence of the mass of a surface magnetopolaron in polar crystals has been discussed by a linear combination operator method by present authors.Most polar crystals are diatomic and cubic and their crystal structure belongs to NaCl,CsCl or ZnS type.The research of these methods only was restricted to the case of crystals having only one mode of the longitudinal optical(LO)phonon.The properties of crystals have been studied by a great variety number of polar crystals,with several atoms per unit cell,have more than one LO phonon branch.For example,in cuprite such as CuO2,there are two LO phonon modes.SiO2,GaAs1-x Px and a large number of perovskites(SrTiO3,BaTiO3,LiNbO3, etc.)have more than two modes.The polaron problem with many LO phonon branches has been studied.The properties of polaron and magnetopolaron in polyatomic polar crystals are discussed by the method of a linear combination operator by one of the authors.However,the influences of magnetic field on the properties of ground state and excited state of a polaron in polyatomic crystals has not been investigated so far.In this paper,the excitation energy and the mean number of phonons in the cloud around the electron of magnetopolaron in a polyatomic crystal studied for the first time by a linear combination operator and a simple unitary transformation methods.The results show that the excitation energy and the mean number of phonons of a magnetopolaron in polyatomic crystals not only includes the coupling contribution between the electron and the different LO phonon branches,but also exists an extra contribution due to crossed terms between the different phonon branches.关键词：polyatomic crystal;linear combination operator;magnetopolaron;excitation energy;mean number of phonon78|69|0更新时间：2020-08-11
- 摘要：With the improvement of experimental techniques and the replacement of equipment, composition and application of solid material have been gained a series new development. So there is continuing interests in polaron. N.Tokuda discussed that the variational law of the ground-state energy, the excited state energies with coupling constant; Xiao Jing-lin, et al. investigated that the properties of polaron in various coupling strength; Xiao Wei, et al. studied that the affact of temperature on polaron; We discussed that the properties of acoustic deformation potential polaron. This paper was going to illustrate the variational law of the effective mass of polaron with temperature and coupling strength.In this paper, the variational relation of the effective mass of polaron in crystals with temperature and coupling strength was derived by using linear-combination operator and unitary transformation method. The results indicated that the effective mass increases with increasing coupling strength when temperature is constant, resulting in the interaction of electron phonon strengthens with increasing coupling strength. The results also illustrate that the effective mass varies with variation of temperature when coupling strength is constant, the stronger coupling strength is, the more obvious the affect of temperature on effective mass. At limit of weak-coupling,the effective mass of slow moving polaron has nothing to do with temperature because a electron is approximate a free-electron at limit of weak coupling and it’s motion is not affected by crystals vibration.In sum, the effective mass of polaron increases with increasing coupling strength when temperature is constant, and affect of temperature on effective mass also increases with increasing coupling strength.关键词：polaron;effective mass104|172|1更新时间：2020-08-11
- 摘要：In recent years, a successful effort has been made to grown Ⅱ-Ⅵ compound semiconductor because of their potential applications in visible light emitting devices in blue green region. ZnSe1-x Tex, with a range of x value, can be either n-type or p-type, was selected as quantum well material. We prepared a (ZnCdTe,ZnSeTe)/ZnTe complex quantum wells structure grown by LP MOCVD on GaAs (100) substrate. The photoluminescence (PL) spectra showed that there were two emission peaks at 2.201 and 2.128eV(labeled I1 and I2, respectively), which was assigned to the emission of Zn0.9Cd0.1Te and ZnSe0.2Te0.8 well layer, respectively. With the increasing of the excitation intensity, the PL intensity ratio of I2/I1 grew significantly firstly, and then decreased slightly. This phenomenon was interpreted in terms of the formation of the build in electric field caused by the different tunneling rates of electrons and holes through the barrier in the structure.关键词：complex quantum well;tunneling rate;photoluminescence spectra87|51|0更新时间：2020-08-11
- 摘要：The paper indicates that ZnS1-xTex alloy thin films have highly efficient light emission. Very strong photoluminescence was observes in samples. The color of the emitted light can be tuned from deep blue to yellow by adjusting Te composition. ZnS1-xTex is a promising material for short wavelength optoelectronic applications and ultraviolet detectors. It’s important that studying the preparation and properties of ZnS1-xTex alloys especially their thin films. And it’s an indispensable work to exploit and apply the alloys. In this paper the ZnS1-xTex polycrystalline thin film preparation by vacuum evaporation and their property studies by AFM(atomic force microscope), XRD(X-ray diffraction), EDS(X-ray energy decompose), UV-visible absorption spectrum and PL(photoluminescence) spectrum were presented. The properties include the morphology, structure, composition, ultraviolet absorption spectra and photoluminescence spectra. The films deposited on glass, quartz glass and silicon substrates. The study of morphology indicates that the ZnS1-xTex thin films are uniformly and polycrystalline in nature. The crystallization of films is good. The average diameter of grain is about 20nm, and the figure is ellipse. The method of vacuum evaporation leads to an inhomogeneity in the difference growth directions. The films belong to zinc blende structure. The comparison between the compositions of Te and S is showed by component studies. The UV visible absorption spectrum shows a very strong absorptive peak in ultraviolet extent and the absorption in visible light extent is low. Photoluminescence spectrum of these films shows an emission centered at 470nm that is in visible light extent. And the spectrum has fine details. The emission can be observed by naked eyes. The results indicated that these films possess some good properties of single crystal films, for example, ultraviolet absorption and photoluminescence.关键词：solid-solution semiconductor;ZnS1-xTex polycrystalline films;vacuum evaporation;ultraviolet absorption;photoluminescence95|49|0更新时间：2020-08-11
- 摘要：Reducing InGaN dimensions is a effective way to increase the work-efficiency of GaN-based light emitting devices (LED). This paper describes our research on the growths of InGaN quantum dots (QDs) and on the analyses of their properties. Instead of the usual Stranski Krastannow growth or surfactant induction, our method consists of three steps: an introduction of second buffer layer on a GaN/Al2O3 substrate, a passivation process for the buffer layer surface at a low temperature, a InGaN QDs fabrication by metal organic chemical vapor deposition (MOCVD). Based on our method, InGaN QDs with high density could be achieved, shown in this paper, we contribute these QDs formation to non-uniform surface-stress at the buffer layer surface. These InGaN QDs have been studied by atomic force microscopy (AFM), transmission electron microscopy (TEM) and photoluminescence (PL) techniques for their microstructure and optical properties respectively. It is shown that InGaN QDs distributed with the density of 1011cm-2 and appeared as cones with about 30nm diameter and 25nm height. The intensity of PL spectrum of InGaN QDs at room temperature is much higher than that of the normal InGaN film grown with the same growth condition, which may be used for making GaN based light emitting devices with high efficiency.关键词：InGaN;quantum dots;induced growth;micro-morphology;luminescence104|180|1更新时间：2020-08-11
- 摘要：White light-emitting diodes were fabricated by phosphor conversion. The blue LED chip (470nm, GaN based) was used as primary light source and Y3Al5O12:Ce3+(YAG) phosphors was used as light changing materials. The excitation spectrum peak of the phosphor is the same as the luminescent peak of blue chip at 470nm. The PL spectrum peak of the phosphors is at 570nm. The white light was yielded by mixing 470nm with 570nm. The luminescent intensity of white LED is 2890mcd. The color coordinates of white LED is x=0.29, y=0.33 and the color index is 77. The efficiency of the white LED is 149lm/W. The light conversion efficiency of phosphors is 269 from blue LED to white LED. The white LEDs with different color temperature from 2700～8000K were fabricated. The relationship between the color temperature and the color coordinates of white LED was investigated. When the color temperature is under 3700K, the color coordinates x and y are bigger than 0.4. When the color temperature is above 8000K, the color coordinates x and y are smaller than 0.3. When the color coordinates x and y are 0.33 respectively, the color temperature is about 5500K.关键词：white LED;blue LED;phosphors129|99|8更新时间：2020-08-11
- 摘要：Strain induced quantum dots (QDs) have attracted more and more attention in recent years due to its potential applications in optoelectronic devices such as light-emitting devices and lasing diodes. Practical devices based on QDs are expected to exhibit high differential gain, low threshold current, and high characteristic temperature comparing with those based on thin films, two-dimensional quantum well and one-dimensional quantum wire structures. To realize these priorities, the study on growth and optical properties of QDs is necessary. Up to now, the study on QDs mainly focuses on Ⅲ Ⅴ systems, In(Ga)As/GaAs system, for example. As for Ⅱ-Ⅵ systems, CdSe/ZnSe attracts most attention. However, The CdSe/ZnSe system, which has relative narrow band gap, can only cover the spectrum range from red to green region. As is known, ZnxCd1-xSe can extend its spectrum to the whole visible range by varying x value. Therefore, the study on the optical properties of ZnCdSe QDs is not only important but also necessary. Additionally, the realization of long lifetime light-emitting devices based on ZnCdSe quantum well structures makes the study more attractive. In the present paper, ZnCdSe QDs have been fabricated under Stranski Krastanow (S-K) mode on GaAs substrate. Atomic force microscopy investigation confirmed the formation of the dots. The excitonic properties of the QDs were investigated by photoluminescence (PL) measurements. The appearance of a kind point in the temperature-dependent PL intensity at about 20K verifies the observation of AFM. With increasing the interruption time between the dot formation and capping, the PL spectra of the QD structures show obvious broadening in full width at half maximum and redshift of peak energy, and the ionization energy, which is induced from the temperature dependence of integrated intensity, decreases significantly with increasing the interruption time. These facts can be attributed to the variations in dot size induced by the ripening process occurring in the growth interruption, in which, the larger dots become bigger at the cost of the smaller ones. Therefore, the PL spectrum broadens because of the increased nonuniformity of the size distribution of the dots. Meanwhile, the peak energy shifts to low energy side, and the ionization energy decreases, resulted from the increase of the dot size. 关键词：ZnCdSe;quantum dot;MOCVD;ripening85|79|0更新时间：2020-08-11
- 摘要：Quantum confinement is an important phenomenon that is being extensively used in making optoelectronic devices with superior properties. In particular, single and multiple quantum wells compose of AlGaAs/GaAs are being widely used, such as high electronic mobility transistors (HEMT) and lasers. With the development of crystal growth technology, MBE has been effectively used in growing such multilayered structures of desirable optical quality. The experimental methods including photoluminescence (PL), Raman resonance scattering, Hall effect, electrochemical C-V profiling, transmitting electromicroscopy and X-ray diffraction were used for study the structure characteristic and photoelectic properties of the materials. X-ray double crystal diffraction and photoluminescence techniques belong to the most sensitive, nondestructive methods of analyzing semiconductor properties. In this paper, we report on structure design and material characteristics of high power InGaAs/AlGaAs/GaAs fold cavity surface emitting laser (FCSEL) with 45° intracavity micro mirror. The epitaxial material for these devices was grown by molecular beam epitaxy (MBE) technique. Optical and structural characteristics of the film were studied by photoluminescence (PL), X-ray double crystal diffraction and electrochemical C-V profiling method. The radiation wave length 0.921μm of sample was obtained at low temperature (10K) in PL spectrum. The experimental results of X-ray double crystal rocking curve and low temperature (10K) PL show the designed structure of folded cavity surface emitting lasers was realized by MBE. The results also show that measuring methods of PL and X-ray double crystal diffraction are very important for testing the quality of quantum wells and improving the MBE technology.关键词：semiconductor laser;surface-emitting;MBE;double crystal rocking curve109|101|0更新时间：2020-08-11
- 摘要：BaFBr:Eu2+ is a kind of photo stimulated luminescence (PSL) material with a wide energy band bigger than 8eV. For BaFBr:Eu2+ powder samples, without pre irradiation of X-ray, VUV or UV light, the radiative transition of Eu2+ ion peaked at about 390nm can be observed, even if the excitation wavelength is longer than 400nm. The electron spin resonance (ESR) spectrum reveals that there are both electron and hole-type traps in powder samples, which play an important role in the PSL process of BaFBr:Eu2+. The slice of BaFBr:Eu2+ powder was fabricated under pressure. Two electrodes were evaporated or glued on the surface of slices, so that we can study the electrical properties of BaFBr:Eu2+, such as the relationship between resistance and voltage, variation of remainder voltage with time and effect of electrode material on it. When a direct current voltage is applied between two electrodes on slices, we have found that at the interface between BaFBr slice surface and electrodes, there exists charge carrier accumulating as a result of the potential barriers, and when the applied voltage was canceled, we can also detect the remainder voltage due to the residual carrier at the interface. The remainder voltage will be decreased with time. When the applied voltage between two electrodes of samples was changed, from higher value to lower one or in inverse direction, the I-V curves, therefore the relationship between resistance and voltage, are different. For different materials of electrode, such as Ag or Cu, if applied voltages are low, the remainder voltage is almost a constant which is only related to the material of electrodes, but, when the applied voltage is high enough, the remainder voltage will decrease with the increase of applied voltage. We believe that this phenomenon might result from the penetration of charge carriers through potential barriers under high applied voltages. The investigation results of electrical properties of BaFBr:Eu2+ show that there exist both electron and hole traps in BaFBr:Eu2+. The trapped electrons and holes are first escaped to conduction band or valence band, and then transported, respectively, to excited or fundamental levels of Eu2+ ion. As a result, the Eu2+ will be excited and its radiative recombination can be observed.关键词：BaFBr:Eu2+;photo-stimulated luminescence;F color center;electrical properties96|96|0更新时间：2020-08-11
- 摘要：Zinc sulfide phosphors are currently of interest for use in a wide range of application including CRT and FED applications. In the engineering of phosphors for low voltage operation, the stoichiometry and composition must be studied and controlled so that the desired objectives of improved powder phosphors can be achieved. This will lead to a better understanding of the processes taking place. The Pb2+ ion belongs to ns2- type impurities. When Pb2+ was added into ZnS, its emissions are probably observed, including blue, green and red emission band. The luminescence properties of ZnS:Zn,Pb was strongly dependent on the preparation conditions. In this paper the luminescence of ZnS:Zn, Pb was studied. The influence of the firing temperature and the Pb2+ concentration used in the synthesis on the origin of the blue luminescence was discussed. After the raw materials was fried at about 950℃ for an hour, the blue luminescence phosphors ZnS:Zn,Pb was obtained. It was shown that ZnS:Zn,Pb gives rather efficient blue emission under low excitation voltages. The brightness of ZnS:Zn,Pb is higher than that of ZnS:Ag,Cl and ZnS:Zn. To explain the origin of the blue emission, the lifetime measurements were performed. A strong decrease of the luminescent lifetime from ms to μs with increasing temperatures was typically found. In view of the similarity in the lifetime behaviour for A-band and D-band emission from Pb2+, the lifetime experiments did not provide evidence for either A-band or D-band emission from Pb2+. It is possible to distinguish between defect related ZnS emission (μs) and Pb2+ related emission bands. For Pb2+ emission band (A-band or D-band) a long lifetime (ms) at low temperatures decreases to μs between ～50K and 150K. It is known that the red emission band was related to the A-band, so the blue emission band was probably related to the D-band. That is mean the D-band emission of Pb2+ in ZnS close to a defect (e. g. S2- vacancy or O2- on S2-site).关键词：ZnS:Zn;Pb;cathodoluminescence;lifetime94|73|1更新时间：2020-08-11
- 摘要：ZrO2,especially in nano scale, with interesting properties in mechanics, thermal, optoelec tronics, has been widely used in ceramic, sensor, high-temperature solid cell, fireproof and wearable materials, etc. With the development of methods for mesoporous materials, mesostructured zirconia has attracted great interest in catalysis, self-organized materials and biomedicine. In this paper, luminescence properties of highly ordered porous ZrO2, synthesized by surfactant-assisted route and post-synthetic treatment of surface modification,were studied and the emission intensity of ZrO2 can be improved after the modification. An aqueous solution of analytically pure ZrSO4·4H2O was dropped into a pure C16TMABr solution under certain temperature and molar ratio during continuous stirring. After stirred for 3h, the mixtures were loaded in PTFE-lined stainless steel autoclaves and heated from 90℃ to 120℃ for 24h. The precipitated products were filtered, washed and dried at 100℃. The dried precipitate was afterwards treated with phosphoric acid solution and then calcined in flowing air at 500℃ for 6h to remove the surfactant. And to modify the surface, some sample were successively dipped into the solution of Zn(Ac)2 and (NH4)2CO3 for about 10h, step by step, and filtered, washed and dried at 100℃. The studies indicated ZrO2 has highly ordered hexagonal pores of about 1.8nm and has strong blue and ultraviolet light emission whose intensity is 100 times higher than that of the bulk samples.Therefore,the luminescence intensity of suface-modified sample is 3 times higher. Under the excitation by 240, 280, 330nm, the emission with the same spectral structure of four emission peaks at 380,410,450,490nm appears,so one can conclude these peaks are related to the same emission center, while the emission ( λem=330nm) excited by 205nm is from a different center.关键词：ZrO2;photoluminescence;surface-modification85|75|2更新时间：2020-08-11
- 摘要：Organic/polymeric electroluminescence (EL) has attracted much attention because of their potential applications in large-area full-color flat-panel displays. Since the first high performance bilayer organic light-emitting device (OLED) was reported by C. W. Tang in 1987, much progress has been made rapidly in this field. Various novel materials have been synthesized, and many significant devices have been fabricated,and application of OLEDs has been realized in commercial automotive audio system and cellular telephone. However, the efficiency and lifetime of the devices still have to be improved. Developing new type organic light-emitting materials will play an important role on overcoming the current problem. Whereas the choice of materials is very important because it decides directly the OLEDs’ performance. So study on new organic materials is the key to improve light-emitting coefficient and long lifetime. OLEDs were made up of polymer or small molecular compound. However, the polymers are usually spin coated, so it is difficult to avoid pint holes and impurities and their influence on the characteristic of light-emitting devices. The small molecule, Alq3 as a typical one, can be vacuum deposited and therefore the films with high purify, high fluorescent efficiency, high crystallizing temperature, stable performance can be achieved, which is important to the fabrication of OLEDs. Whereas it is expected to obtain a compound that has a resemble structure with Alq3, excellent stability and luminescence properties. In this paper, a new light-emitting material ZZnqCl2 was synthesized; ZZnqCl2 thin films were deposited by using thermal deposition technique. Light emitting devices were prepared using ZZnqCl2 as light-emitting layer. There has not been any report on this type of compound so far to our knowledge. The details of an experimental study on the deposition process of ZZnqCl2 thin films and devices, and their photoelectric properties were given in this paper. It is demonstrated that such films can be deposited by convenient thermal evaporating technique, and a light-emitting devices is prepared successfully. The films were characterized by ultraviolet spectroscopy (UV), and photoluminescent spectroscopy. Optical absorption and fluorescent spectra of the films were measured. Significant fluorescence was detected and the spectrum was recorded in which two peaks at 406.4, 540nm were observed respectively.113|60|1更新时间：2020-08-11
- 摘要：Organic thin film transistors and electronics are of interest for low cost high information content displays, especially on flexible substrates, and for other large area electronic applications. Ambipolar field-effect transistors, which operate as either n or p-channel devices, depending on the polarity of the gate bias, can operate in a mixed or bipolar mode. They have been realized with amorphous silicon, organic semiconductor heterostructures, and organic single crystal. We report here on the structure and operating characteristics of an ambipolar organic light emitting field-effect transistor based on single crystal of the pentacene. The electrons and holes are injected equally from the source and drain respectively and the drain current can be controlled by the adjusting gate and drain source voltages. Excitons are generated, leading to radiative recombination. We grown the single crystal thin film based on pentacene by physical vapor deposition and fabricated organic field-effect transistor using it. The thickness of the film is about some few micrometer and the length is about some few millimeter. The proportion between the length and thickness is about 1000. Using polyimide as bond organic thin film was tiled on the glass substrate. By magnetic controlled sputtering method, choosing appropriate condition of sputtering, Al as source drain electrode, Al2O3 as insulation layer and Al as gate electrode were obtained. Then, we measure I-V characteristics and discuss luminescence principle about organic field-effect transistors. The most important two factors of the success are the use of organic single crystal with high mobility and the employ of the field-effect structure to control injection for the ambipolar organic light emitting field-effect transistor.关键词：pentacene;organic single crystal thin film;light-emitting field-effect transistor101|101|0更新时间：2020-08-11
- 摘要：The Raman measurements have been performed with the back-scattering geometry on the SiC films grown on Si (100) and sapphire (0001) by LPCVD. Typical TO and LO phonon peaks of 3C-SiC were observed for all the samples grown on Si and sapphire substrates, indicating the epilayers are 3C-SiC polytype. Using a free-standing 3C-SiC film removed from Si(100) as a free-stress sample, the stresses of 3C-SiC on Si (100) and sapphire (0001) were estimated according to the shift of TO and LO phonons.关键词：3C-SiC;Raman spectrum;Si(100);sapphire (0001)143|125|3更新时间：2020-08-11
- 摘要：Using the backscattering geometry micro Raman microscopy, the a:Si film which made by PECVD was crystallized, and measured by the same instrument. The laser power density was about 8.3×105W/cm2 when using 100×objective (N. A.=0.9) and 6.1×105W/cm2 when using 50×objective( N. A.=0.75) to crystallizing. The wavelength of laser is 632.8nm (He-Ne laser). Based on the confocal Raman spectrometer and depth profile method, we collected the series of Raman spectrum of silicon film that the focus laser spot located the different depth in the amorphous silicon film when processing the laser crystallization. Through the Raman Stokes peak and anti Stokes peak of microcrystallite silicon film which have been laser crystallized, we can calculate the maximum temperature of the amorphous silicon film was about 1600K in the process of laser crystallized. At the same position on the sample, reduced the laser power density to about 6×104W/cm2 (the laser of this power density can not effect the character of the microcrystallite silicon film), repeating the Raman depth profile experiment and getting the series of Raman spectrum. After curve fitting these Raman spectrum of the laser crystallized silicon film, the Raman spectrum mainly fit to five peak (crystal silicon peak about at 520cm-1, amorphous peak about at 480cm-1 and others three peaks), we got the area of crystal silicon peak and amorphous silicon peak which attribute the degree of laser-crystallized and we discover crystalline phase located only in the middle of thin film. According to the Raman shift of the peak of crystal silicon, we estimated the size of crystal grain was about 5nm. By this way, the nanocrystal silicon material in the thin film have been achieved, and the character of crystalline phase in laser-crystallized poly-Si thin films has been researched.关键词：nano-μc-silicon;confocal Raman microscopy;depth profile;laser crystallize101|100|2更新时间：2020-08-11
- 摘要：Iron nitride films have received attention for many years. Initially, they have been studied because of their ability to improve surface hardness and wear resistance. Recently, the FeN thin films have been widely investigated since they show a variety of structures and magnetic properties. All nitrides with the composition of FexN(x≥3) are ferromagnetic and stable at room temperature. In particular, α″-Fe16N2 phase is the most important compound and can be a possible candidate for high density magnetic recording media owing to its very high magnetic moment even higher than that of pure iron. However, up to now, little research has been done to investigate the dynamical scaling behavior of iron nitride films sputtered on glass to determine its universality class although dynamic scaling may be a useful method for understanding the formation of structure of the thin films. There are three types of growth morphologies:layer by layer growth, unstable growth, and self affine surface. Solid films grown under far from equilibrium conditions are predicted to have self affine surfaces, and the roughness can be characterized by appealing to a dynamic form. Moreover, the KPZ equation has proven to be a universal equation for real surface growth phenomena only on the basis of computer simulations. There is nearly no unambiguous experimental demonstration of KPZ growth. In this study, we deposited iron nitride thin films by DC magnetron sputtering at mixed Ar/N2 discharges(N2 fraction of 5%,10%,30%,50%, respectively) and different times(160,30,20,10,5min) in order to study their kinetic scaling behavior. The composition of the films was analyzed using X-ray photoelectron spectroscopy experiment (XPS). The layer phases and surface morphology of the films were characterized using grazing incidence X-ray scattering and X-ray diffraction as well as atomic force microscopy. For the film grown at N2 fraction of 30% and 50%, the phase of FeN appears, if the N2 fraction is 10%, the phase of ε Fe3N is formed, while the phase of FeN0.056 occurs for the film deposited at N2 fraction of 5%. The surface of the films deposited at N2 fraction of 5% showed a self affine character. The values of roughness exponent α≈0.65 and growth exponent β≈0.53±0.02 are in agreement with the improvised KPZ exponents based on Kolmogorov’s energy cascade concept.关键词：iron nitride thin films;kinetic scaling;DC magnetron sputtering91|74|0更新时间：2020-08-11
- 摘要：Permalloy Ni80Fe20 films (about 80nm thick) have been prepared by magnetron sputtering. The substrates were Si (111) single crystal wafers on which 500nm thick SiO2 were formed by thermal oxidization. The films were deposited at 300,643 and 823K in 0.45Pa argon pressure. The base pressure in our vacuum chamber was about 4×10-5 Pa. The deposition rate was about 3nm/min for all the films. The structure of the films, grain orientation, cross section morphology, grain size and surface roughness were characterized using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The resistance and magnetoresistance of the films were measured using four point probe technique. The results show that with rising substrate temperature the crystallization become notable and the texture of (111) orientation developed gradually in the growing films. As a result, the resistance decreased evidently and magnetoresistance ratio increased markedly.关键词：permalloy film;magnetron sputtering;structure;magnetoresistance87|109|0更新时间：2020-08-11
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