最新刊期
卷 25 ， 期 3 ， 2004
- 摘要：In the past decade, electroluminescent devices based on organic materials are of considerable interest to their attractive characteristics and potential applications. The study and application of organic light emitting have made significant progress. Organic light emitting devices (OLEDs) have many advantages such as their thinness, self light emission, broad viewing angle, quick response, high efficiency, easy fabrication, low driving voltage, low energy consumption, low cost, etc. It is therefore very possible that they will become the next generation of panel displays. White organic light emitting devices have been attracting particular attention nowadays due to their potential applications as full color displays, backlights for liquid crystal displays and even paper thin next generation of light sources. The emitting materials used in OLEDs can be divided into fluorescent and phosphorescent materials. Phosphorescence is distinguished from fluorescence by the speed of the electronic transition that generates luminescence. Both processes require the relaxation of an excited state to the ground state, but in phosphorescence the transition is "forbidden" and as a consequence it is slower than fluorescence, which arises from allowed transitions. Indeed, phosphorescence may persist for several seconds after a phosphorescent material was excited, whereas fluorescent lifetimes are typically on the order of nanoseconds. Interest in phosphorescence, and the phosphorescence of organic materials in particular, arises from the application of these materials to organic light emitting devices (OLEDs), where it is found that the luminous efficiency may be improved by up to a factor of four over that obtained using fluorescence. This increase is fundamental to organic materials and arises during the formation of an excited state (or excitons) from the combination of electrons and holes. To achieve white emission in OLEDs, an additive mixture of the three primary colors or two complementary colors are required. Various methods have been demonstrated to produce white light emission from organic OLEDs, including mixing of the three primary colors (red, green and blue, RGB) from respective layers in a multilayer structure, doping a single host emissive layer with RGB emitting materials, or utilizing of broad exciplex or excimer emission. White emission could also be achieved by mixing a blue host with an appropriate amount of yellow or orange dopant in a single emissive layer. The development of white organic light emitting diodes has been described and discussed on the materials, the device structures and the light emitting mechanisms have also been given.关键词：organic light emitting diodes;white light emission;device structure;light emitting mechanisms104|524|4更新时间：2020-08-11
- 摘要：Bis-2-(2-hydroxyphenyl)benzothiazolate)zinc (Zn(BTZ)2) is one of the best white electroluminescent materials used in organic light emitting diodes (OLEDs). White light, which is composed of three discrete peaks in R/G/B regions, is very important and particularly useful for full color display. However, most of white OLEDs, so far, are fabricated with multilayer structures, which results in the complication of fabrication process and decline of quantum efficiency. So these devices are not suitable for the purpose of large scale industrial manufacture. In this paper, firstly, Zn(BTZ)2 had been synthesized from the complex reaction between zinc acetate dihydrate and 2-(2-hydroxyphenyl) benzothiazolate. Then we used Zn(BTZ)2 as main light emitting material and fabricated two types of organic white light emitting devices. The configurations of the devices are as follows: ITO/PVK: TPD/Zn(BTZ)2/Al and ITO/PVK:TPD/Zn(BTZ)2:Rubrene/Al. The bright and steady light emitting had been obtained, and the brightness of the devices came to 3200cd/m2 and 2900cd/m2 (at a driving voltage of 16V), respectively. We also measured the CIE coordinates of the above devices, they were (x=0.242, y=0.359) and (x=0.324, y=0.343), respectively. The latter CIE coordinate is very close to the equi energy point (x=0.33, y=0.33), and the corresponding quantum efficiency value is 0.47%. This value is higher than the former one, which is 0.32%. Details on the white light emitting characteristics of the devices were explained by the curves of current den sity voltage, optical current voltage and quantum efficiency current density, they were measured using a quantum efficiency measure system including the Keithley 485 Picoammeter and 2400 SourceMeter. We also discussed the emitting mechanisms of the material and the devices at last.87|60|3更新时间：2020-08-11
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Narrow-line Light Emission from 8-Hydroxyquinoline Alumina Assembled in Porous Silicon Microcavities
摘要：The spontaneous emission of a material can be controlled by placing it in a micron sized optical cavity. In this paper we assembled 8 hydroxyquinoline aluminum (Alq3) into porous silicon microcavities(PSMs) fabricated by pulsed electrochemical etching. The pulsed current etching is superior to DC etching in obtaining flat interfaces within the distributed Bragg reflectors because of its minor lateral etching. The measured peak reflectivity of the microcavities before the impregnation is 99.5%,and its full width at half maximum(FWHM)is Δλ=6 nm,and after impregnation Δλ=15nm. The spontaneous emission spectrum of the optically excited 8 hydroxyquinoline aluminum is drastically modified by micro cavity effects. Compared with the luminescence of a filled single P Si layer with the same thickness as the microcavity, and with an average of the porosity of the layers constituting the microcavity, the full width at half maximum of PL spectrum in a filled microcavity is drastically reduced from 85 nm to 15 nm, the peak emission intensity increased by one order.However,beside the resonant peak of PSMS, the weak side peaks origina ting from PS can be observed, because the reflectivity of the microcavities is decreased in this region. Random porous silicon dielectric multilayers are proposed as interesting materials for application as optical components. The use of random instead of periodic multilayers has the advantage of obtaining a wider stop band in Bragg reflectors with the same difference in the refractive indexes of the layers and in a higher finesse in Fabry Perot filters. In the case of Alq3 being impregnated into random FP interference filter, the off resonant optical modes are highly depressed. The experimental results suggested that the porous silicon microcavities is a good encapsulated media for Alq3, and Alq3 emission properties was improved by the microcavities. This may make a new way for Alq3 in application in electroluminescence.关键词：porous silicon microcavity;8-hydroxyquinoline aluminum;photoluminescence94|70|0更新时间：2020-08-11 - 摘要：The determination of the structure of light harvesting complex Ⅱ and the development of ultrafast technique provide us the possibility to investigate the mechanisms in primary process of photosynthesis. Femtosecond (fs) pump probe technique at different wavelengths and time resolved photoluminescence technique (TRPL) were used to study photoinduced ultrafast dynamics processes in the LHCⅡisolated from the leaf of soybean. A mode locked Nd:YAG laser served as the excitation source in the TRPL measurements, and the excitation wavelength could be tuned from 570 nm to 610 nm with 10 ps pulse duration. The anisotropic dynamics were observed from TRPL spectra of LHCⅡ at different temperature, indicating that the energy transfer among pigments is affected by temperature. In the femtosecond pump probe measurements, Ti:sapphire laser and an optical parametric amplifier (OPA)were used as excitation source to generate tunable infrared laser pulses at wavelength from 1.1μm to 1.4μm. By using a YCOB crystal, second harmonic beam at visible light was obtained to be applied as the laser source in our measurements, which could be tuned from 550 nm to 700 nm with 150 fs pulse duration and 1 kHz repetition rate. From the femtosecond dynamical results, it could be observed the energy transfer processes between Chl a Chl b and Chl a Chl a pigments at different sites. The dynamical traces demonstrated that the energy relaxation from Chl b to its neighboring Chl a takes place in 200～300fs time region, the excitation relaxation between the excitonic states of Chl a in several hundreds of femtoseconds, and the energy equilibrium process of intermolecular of Chl a in several picoseconds. The observed slower decay component with the time constant up to hundred picoseconds from time resolved fluorescence and femtosecond dynamics traces could be assigned to the change of molecular conformation or energy equilibrium in LHCⅡ. These results have some significance in understanding the photophysical and photochemical mechanism in primary process of photosynthesis.关键词：photosynthesis;LHCⅡ;energy transfer;ultrafast process94|112|0更新时间：2020-08-11
- 摘要：Protein and Bilirubin(BR) are the main components in animal bile. When the metabolization is disordered, the unnecessary and free bilirubin can combine with some proteins to form compositions and produce toxin. To learn the mechanism of toxicity, the effects of bilirubin on the molecular structure of Hemoglobin(Hb) and the means of their combination were studied by fluorescence and UV absorption spectra. It was shown that BR can quench the fluorescence of Hb extently,which decreased the fluorescent intensity of tryptophan(Try) at 330 nm and the peak at 410 nm disappeared; at pH 9.4 BR can bind with Hb in cooperative actions of nonelectrostatic attraction, e g. Hydrophobic action, Van der Waals force. The intensity declinded with the delay of time. The group of -NH2 on the Try residue of Hb molecule reacted with two -COOH groups, and formed a complex with curly structures. The spectra can vary with temperature, the conformation of BR changed from Z-Z to Z-E or E-Z, which caused complex structures. It showed two peaks at 350 nm and 406 nm induced by dipyrrole chromphoses of BR,the absorption fissions occurred in Hb UV spectra. Therefore, the present of free bilirubin molecules damaged the structure of Hb molecule and the spectra appeared different. It is less reported about the interaction of Hb and BR at present, the discussions in this paper provide experimental information for the study on medicine and biochemistry, and also offer some theoretical bases for the relation between biological macromolecules and organic micromolecules.关键词：bilirubin;hemoglobin;fluorescence;UV absorption spectra110|147|3更新时间：2020-08-11
- 摘要：Rare earth solids are important materials widely used in optoelectronics. The notable examples are Nd:YAG as laser materials and Er doped fiber as optical amplifier for optical communication. The ultrafast properties of rare earth materials have not been extensively studied before. However, due to the present development of information technology characterized with broadband signals and tera bit rate data transmission, it is very important to understand the interaction between the rare earth ion and its solid environment, and their corrected role in the coherent dynamic processes. In trivalent rare earth solids, the optically active center involves intra-4f electron transitions. The 4f electrons are well shielded from the crystalline environment by their outer 5s5p electrons. The resulting sharp absorption or emission spectra indicate long surviving optical coherence among various 4f electronic states even at room temperature. We report both time domain and frequency domain linear spectroscopies in the study of coherent dynamic in rare earth powder Eu3+:Y2O3 at room temperature. The time domain free induction decay was obtained via an interferometric fluorescence measurement with a pair of phase corrected femtosecond pulses, while the frequency domain signal is via steady state fluorescence excitation. The recorded interferogram exhibits beatings in picosecond time scale arising from the interferences among various weakly split of 4f electronic states. The separation of the involved energy levels deduced from the beating is approximately 1.1 nm, in agreement with that obtained from the excitation spectra. Analysis with the theory of multi level excitation resulted quantum interference shows that the experimental results can be well explained. Rare earth is often used as gain medium of laser, one gain curve include many stark split electronic levels. The long coherent relaxation time indicates its possible to enhance the population of one electronic level while depressing the population of other electronic levels by quantum interference control. The research on quantum interference of rare earth ions shows its potential application in stimulated light amplification.92|69|0更新时间：2020-08-11
- 摘要：With the development of molecular beam epitaxy (MBE) technology and metal organic chemical vapor deposition (MOCVD) technology, there has been great interest in investigating quantum dot both in material science and condensed state physics field. Due to size of quantum dot was small, they had a series of new and serious character, for example, quantum size effect, quantum coherent effect, quantum tunnel effect, coulomb resistance effect and surface effect, etc., these had brought infinite chance and hope on development and use of new materials. Especially, electron in quantum dot was subject to a strong three-dimension (3D) confinement, so that quantum effect was quite different from those of the bulk materials, these would brought about great society benefit and economic benefit. So many scientists has been investigating properties of quantum dots. Zhu J L, et al. studied the properties of spherical quantum dot by using a few bodies method, results indicated that binding energy of donor state had depended on shape, dimension and confined potential of the quantum dots. Charrour R, et al. studied the ground state binding energy of hydrogenic impurity in cylindrical quantum dot that subjected to external strong magnetic field by using the variational procedure and considering an infinite confined potential on all surface of the system. They found that the impurity binding energy depended strongly on the impurity position, magnetic field strength and the dot size(radius and height). Zhou H Y and Gu Shiwei had studied the properties of strong-coupling magnetopolaron in a disk-shape quantum dot, they pointed that the ground state energy and the excited state energy depended on resonance frequency and confined strength. The properties of magnetopolaron with electron-LO-phonon weak-coupling in cylindrical quantum dot, which was in parabolic potential, were investigated by using the linear combination operator and unitary transformation methods. Numerical calculations for ZnS quantum dot indicated that the ground state energy increased with increa sing characteristic frequency and cyclotron-resonance frequency,since vibration energy increased with increasing characteristic frequency and additional energy in external magnetic field increased with increasing cyclotron-resonance frequency, the energy of magnetiopolaron changed position from negative when characteristic frequency(or cyclotron-resonance frequency) increased to the value,for example, which was 0.27ωLO for the case of cylinder height L =20 nm and cyclotron resonance frequency ωc=0.5ωLO (or ωc was 0.5ωLO for the case of L=20 nm and characteristic frequency ω0=0.27ωLO ). The ground state energy increased with increasing cylinder height, the smaller cylinder height was, the faster it increased, the energy of magnetopolaron also changed positive from negative when cylinder height decreased to 33.1 nm for the case of ωc=ω0=0.5ωLO. In short, ground state energy of bounding magnetopolaron in cylindrical quantum dot had something to do with size of quantum dot, external magnetic field and characteristic frequency.关键词：quantum dot;magnetopolaron;characteristic frequency82|87|0更新时间：2020-08-11
- 摘要：Many experimental results and theoretical analysis diverge mostly because different preparation conditions can seriously affect on PL properties of porous silicon. Specimens of porous silicon were prepared under different conditions by double cell positive pole oxidizing method and their photoluminescence properties were analyzed systematically. Firstly, specimens were prepared in the same solution concentration (V (HF): V (C2H5OH)=1:1) and erosion time (20 min) but under different oxidizing current density. Secondly, specimens were prepared in the same solution concentration (V (HF): V (C2H5OH)=1:1) and current density (3mA/cm2) but for different erosion time. Thirdly, specimens were prepared in the same current density (3mA/cm2) and erosion time (20 min) but with different solution concentration. And then photoluminescence spectra of these specimens were measured at room temperature. Fourthly, photoluminescence spectra of the specimen, which prepared under the conditions of solution concentration (V(HF): V(C2H5OH)=1:1) and current density (3mA/cm2) and erosion time (20 min), were measured respectively at room temperature after it had been lain in the air for three days, sixteen days and thirty days. Results suggest that, with the increasing of the current density, erosion time and the aging time, the peaks of PL shift to the blue, and the intensity of peaks is enhanced. But excessive current density and erosion time would cause the decrease of PL intensity. As for the solution concentration, peaks shift to the red when solution concentration is less than 1:1 but shift to the blue when solution concentration is greater than 1:1 with the increase of solution concentration. Above phenomena can be interpreted by quantum confinement model and light center model, as well as the action of Si-H bonding and other defects. In the process of porous silicon photoluminescence, peak shift and intensity change by current carrier limitation and surface passivation action. Increasing current density can produce more pits during initial stages of erosion, and can enhance hole energy in bulk silicon, and it is favorable for F-to go through potential barrier located at Si/HF interface to silicon surface, therefore quantum wire produced at silicon substrate can become thinner. To prolong erosion time can make quantum wire thinner too. The influence of solution concentration is more complex. The influence of aging time on peak position and intensity is obvious, and show that porous silicon quality is not steady.关键词：porous silicon;preparation conditions;photoluminescence spectra94|134|1更新时间：2020-08-11
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High-power AlGaAs/GaAs Single Quantum Well (SQW) Remote Junction Lasers and Its Aging Characteristic
摘要：For conventional high power quantum well (QW) lasers whose p-n junction is located in or near the active region, the dark spot defects (DSDs) and the dark line defects (DLDs) develop and move to the active layer during aging process, which increases non-radiative recombination centers and causes device to degrade. As a result, the threshold current increases, while the output power and the differential coefficient decrease at the same time. However, for the RJ lasers, the p-n junction is separated from the active layer by the presence of a thin waveguide layer between the active layer and p-n junction. The mobile defects are absorbed in the p-n junction located outside the active layer because of the electric field of p-n junction. Thus, the non radiative recombination centers in the active layer decrease, the degradation of RJ lasers is decided by the degradation of p-n junction. Unless the p-n junction suffers serious damage, a much longer lifetime and a better reliability may be expected for RJ lasers. We designed and succeeded in fabricating 808 nm AlGaAs/GaAs separate confinement heterostructure(SCH)single quantum well RJ lasers with a cavity length of 900 μm and a stripe width of 100μm by depositing the material on GaAs substrate with metal organic chemical vapor deposited (MOCVD). Its epitaxial structure is different from the conventional 808 nm AlGaAs/GaAs SQW semiconductor lasers. The SCH active region consists of a 10 nm thick Al0.07Ga0.93 As layer between two 0.1 μm thick p-Al0.3Ga0.7 As waveguide layers. One p-Al0.3Ga0.7 As layer separates the active layer from the p-n junction, and also carries out optical and carrier confinement together with another p-Al0.3Ga0.7 As layer. The n and p cladding layers are each 1.3 μm thick. Compared to the conventional 808 nm GaAs/AlGaAs high power SQW laser structure, there is a 0.1 μm thick p AlGaAs layer between the p-n junction and active region, as shown in Table 1. To decrease the effect of dislocations in substrate on the epitaxial layer quality, a n+-GaAs buffer layer is grown between the substrates and n-Al0.5Ga0.5 As lower cladding layer. The DC characteristic of RJ lasers was measured. Compared with the conventional AlGaAs/GaAs high power semiconductor laser, the remote junction (RJ) high power semiconductor laser shows that the threshold current (Ith) and the threshold voltage (Vth) are large. During 3000 hour constant current LD mode aging process, the RJH lasers showed a reduction of threshold current and a fluctuate increase of output power.关键词：high-power semiconductor laser;remote junction;single quantum well (SQW);AlGaAs/GaAs97|107|0更新时间：2020-08-11 - 摘要：ZnO film has attracted more and more interest since its UV lasing was reported on "Science" (1997). A lot of sources, such as Xe lamp, YAG:Nd laser and cathode ray, have been used as the excitation sources to investigate the luminescence of ZnO thin film. In the present work, synchrotron radiation light (VUV) of HASYLAB in Hamburg, Germany was applied to study the UV luminescence of ZnO thin film. The UV luminescence of ZnO thin film on Si substrate at different temperatures (7～300K) were observed using synchrotron radiation light (195nm) as excitation source. Its emission spectra include three different band peaking at 380, 369.5, 290nm, respectively. Each of the three bands has different decay time and different temperature dependence, but they all have the same excitation spectra. The strong excitation band is in VUV range (100～200nm) instead of near UV range. Combining the calculated results of ZnO electronic structure and experimental data, we suppose that the VUV excitation (6～10eV) can be attributed to the excitation of electrons in the lower valance band of ZnO, which mainly consists of Zn3d states with bound energy from 4.0～6.5eV. The origin of the three different UV emission bands was also discussed. 369.5nm emission is from free exciton recombination, and 380 nm broad band is related to the inter band transition, while 290nm emission may be corresponding to the recombination of the electron in the secondary energy well of the conduction band with the hole in the valance band, or may be come from structural defects.关键词：ZnO film;luminescence;vacuum ultraviolet (VUV);spectroscopic property116|91|6更新时间：2020-08-11
- 摘要：As a wide-gap Ⅱ Ⅵ oxide semiconductor, ZnO is known to have a band gap of about 3.3eV and large binding energy of excitons (59meV) at room temperature. Recently, ZnO-based semiconductors and related heterostructures are attracting more interest because of their promising optoelectronic applications in the ultraviolet wavelength range. To obtain the high performance light emitting devices, the key technique is to construct a heterojunction to realize double confinement action to electrons and photons in optoelectronic devices. MgxZn1-xO alloy thin films have been studied extensively as their potential barrier materials. MgxZn1-xO alloy thin films were fabricated on c plane sapphire (Al2O3) substrates by plasma assisted molecular beam epitaxy (P MBE). The films with different composition x, which is changed from 0 to 0.20, kept wurtzite crystal structure measured by X ray diffraction (XRD). X ray double crystal diffraction spectra show that the samples are single crystal films. As x value was increased from 0 to 0.20, the full width at half maximum (FWHM) of (002) oriented ZnO X ray rocking curve is broadened from 0.25° to 0.71° and the lattice constant of c axis is decreases from 0.5205nm to 0.5185nm. Photoluminescence (PL) spectra at room temperature(RT)exhibit an intense ultraviolet emission, without the deep level emission. With increasing x values, FWHMs of the emission peak change from 62meV to 89meV and peak positions shift to high energy side from 3288eV to 3467eV. The absorption edges of alloy thin films show the blue shifts with increasing x value in the transmission spectra at RT. The origin of the ultraviolet emission is studied by the measurements of the PL spectra at different temperature. The result shows that this emission comes from the recombination of neutral and ionized donor-excitons. Two steps dissociation process of neutral donor-exciton complexes is found, in which the thermal quenching mechanism is attributed to the dissociation of a free electron from the complex and the dissociation of two free electron and a free hole from the complex.关键词：MgxZn1-xO;P MBE;X ray double crystal diffraction;photoluminescence90|53|2更新时间：2020-08-11
- 摘要：The ZnO thin film has been deposited on Al/Si(100) substrate by direct current (DC) reactive magnetron sputtering method. The ZnO Schottky Barrier Diode (SBD) has been fabricated using Al and Pt as ohmic and Schottky contacts, respectively. X-ray diffraction (XRD) measurement indicated that the ZnO thin film was well c-axis oriented. The atomic force microscope (AFM) showed that ZnO thin film had a smooth surface and the grain size was about 100nm. The spreading resistance profile (SRP) indicated that the thickness and carrier concentration of ZnO film was 0.4μm and 18×1015cm-3, respectively. The Hall effect measurements showed that ZnO thin film was of n type conductivity. The current voltage measurements indicated an evident rectifying characteristic of ZnO SBD. The barrier height between Pt and n-type ZnO was 0.54eV. This is the first attempt toward ZnO thin film SBD, which has not been reported before and the performance of the ZnO SBD could be improved by optimizing the device structure and technology.关键词：ZnO thin film;Al/Si (100) substrate;Schottky barrier97|95|4更新时间：2020-08-11
- 摘要：By using the molecular beam epitaxy (MBE) and plasma assisted MBE with oxygen atmosphere, the ZnO thin films were deposited on Si(100),GaAs(100) and Al2O3 (0001) substrates with Zn,ZnS,or Zn-O buffers respectively,under different temperatures of beam source and of substrate. The buffer layer is necessary for preparation of ZnO thin film, in order to minimize the effect of mismatch of crystal lattice between substrates and ZnO. In the X-ray diffraction spectrum, we can observe peaks specific to ZnO at (100), (002), (101), (102), and (103). There are some shifts of diffraction peaks for ZnO thin film at different substrates. The atomic force microscope images (AFM) show that the ZnO films are composed of small granules with nano size. The thickness of film was found about several nanometers, by using the grazing incidance X ray reflectivity method. Under the excitation of 360 nm, the photoluminescence of ZnO films is a broad spectrum with peaks at 410 and 510nm. We suggest that the luminescence is due to deep levels related to the oxygen defects at the surface.102|102|2更新时间：2020-08-11
- 摘要：Highly orientated(002) polycrystalline ZnO films with hexagonal structure have been deposited by using r. f. magnetron sputtering. Strong monochromatic green photoluminescence (located at 514 nm) has been observed in these non intensively doped ZnO films when exited with 320nm light.For the vacuum annealed samples at 830℃, the intensity of the green PL increases markedly. On the contrary, for the samples annealed in oxygen, the intensity of the green PL decreases rapidly. The green emission may correspond to the electron transition from deep oxygen vacancy level to the valance band.关键词：ZnO films;magnetron sputtering;green PL85|108|7更新时间：2020-08-11
- 摘要：The p-ZnO and the ZnO p-n homojunctions on n-Si(110) were grown by the methods of RF and DC reaction magnetron sputtering. An oxygen rich condition has been kept in growing process of the p-ZnO. The FWHM of the ZnO (002) diffraction peaks are 0.3° obtained by XRD measurements. A hexagonal self-assembled structure of the ZnO films is shown by atomic force microscopy. The 390 nm UV emission peak of the ZnO films present in the cathodoluminescence spectra. The I-V property of the ZnO p-n junction was measured by an I-V character. The curve indicates a value of 1.1 volts forward threshold, which is equal to the results of the ZnO p-n junction grown in Japan and America using DC sputtering method and diffusion method; meanwhile the backward characteristics of our sample is much better.关键词：ZnO;p-n junction;silicon;I-V property97|66|1更新时间：2020-08-11
- 摘要：ZnO with various nano structures have tried to be prepared due to the special features of nano structured material. In this work, the web like structured ZnO clusters (WLSZC) have been prepared for the first time. The first step of this process is to prepare the colloidal Zn(OH)2 by means of co preparation process. The second step (the key step to prepare WLSZC) is to treat the yield colloids using ultrasonic machine for 70 min. The third step is to sinter the as treated colloids in step 2 and obtain the WLSZC. The as-prepared samples are characterized by the high resolution transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. In WLSZC, we observe homogeneous polygons which consist of one single-crystal particle at each side. In addition, the samples in this order demonstrate that with the decreasing of the ultrasonic treatment time, the size distribution decrease, the mean size increase, and less aggregation is found. The formation of WLSZC can be explained by the following reasons: the structural difference of as-prepared samples can be attributed to the ultrasonic treatment and the duration of treatment. Colloid in de ioned water exposed to the ultrasonic standing wave (USW) is driven by an axial direct radiation force to concentrate at nodal. The longer the treatment time, the thinner the plane. Because the size of particles in the sample depends on the thickness of the plane, therefore the longer the treatment time, the smaller the particle size. The particles move toward and accumulate at preferred positions within the nodal plane and after enough treatment time a pre-web-like structured colloidal cluster is likely to form. The pre web like structure is presumably of more colloid in polygon side positions of WLSZC and less colloid in porous positions of WLSZC. From Sample B to Sample F, with less and less treatment time, the size distributions were narrower due to less and less accumulation. Unlike other worker’s results, the six samples evince just one very broad emission band with a peak at 469 nm and with fourfold splitting line. The PL intensity of Sample A is 8～14 times larger than those of other samples (B-F). This phenomenon is due to the resonant effect of the polygonal pores (about 100 nm wide). In addition, the in plane movement of colloids was attributed to lateral variations within the nodal planes of ultrasonic sound giving rise to a lateral radiation force (perpendicular to the nodal plane) that probably produced internal stress along the direction perpendicular to the nodal plane in the colloid clusters, as well as probably remained in the samples along the direction perpendicular to the nodal plane. Due to combination of unaxial residual stress and spin exchange a fourfold spin splitting of donor-acceptor transition is observed in the as-prepared samples.The PL spectrum of the web like structured ZnO indicates that the web like structure would results in increasing PL intensity.88|56|0更新时间：2020-08-11
- 摘要：ZnO, a Ⅱ Ⅵ compound semiconductor with a wide direct band gap of 3.37eV at room temperature, is a multi functional material which can be used in varistors, phosphors, gas sensors, transparent conductive thin films and surface acoustic wave devices, etc. We prepared ZnO thin films on c plane sapphire substrates by metal organic chemical vapor deposition and investigated thoroughly the structure and optical properties by X ray diffraction (XRD), Raman spectrum, X-ray photoelectron spectrum (XPS) and photoluminescence (PL) spectrum. ZnO thin films were fabricated on (0001) sapphire at optimized temperature of 580℃ under the reactor pressure of 480Pa by using a low pressure MOCVD apparatus. Diethylzinc (DEZn) and oxygen as the reactants were introduced into the reactor separately. The structure and crystallinity of the ZnO thin films were characterized by XRD. Only (0002) diffraction peak of ZnO with hexagonal wurtzite structure could be observed. The diffraction peak positioned at 2θ=34.48° and the value of the full width at half maximum (FWHM) was 0.184°, which implied a good crystalline quality of ZnO thin films. The lattice constant calculated were 0.3261nm and 0.5198nm for a and c axes respectively. It could be concluded that the tensile stress along the a axis exist in the ZnO thin film. The averaged grain size was 47.12nm. Raman scattering spectrum of the ZnO thin films was performed at room temperature. E2(high) mode and A1(LO) mode were at 435.32cm-1 and 575.32cm-1 respectively. The former corresponded to the band characteristic of wurtzite phase, while the latter was related to the formation of oxygen deficiency, interstitial Zn and free carrier. Both modes shifted to high frequency side due to the tensile stress along the a axis. In addition, X ray photoelectron spectrum showed that O2 could adsorb in the surface of the sample. After etching for 10 minutes, the quantity of O2 adsorbed was reduced and the binding energy of O1s was 530.2eV, which was close to that in Zn-O bond. Simultaneously, the PL spectrum of the ZnO thin film was measured. A strong near band edge (NBE) emission was obviously observed, which was at 3.28eV with the FWHM of 125 meV. The deep level emission (DLE) centered on 2.55eV was quite weak. The ratio of the intensity of the NBE to that of DLE was 40:1, which suggested better optical quality of the ZnO film grown by MOCVD at the present growth conditions.关键词：ZnO thin film;MOCVD;PL;structure91|77|3更新时间：2020-08-11
- 摘要：The photoelectric translating efficiency of the ZnO film is a very important parameter of ZnOs photoelectric characters, which especially is useful on solar cells. Generally the photoelectric property of ZnO can be enhanced by using n type impurity dopants. But we discovered that the intrinsic defects can still make effective action even if the ZnO have doped by n type impurity dopants. In the process of DC reactive sputtering, an appro priate pressure proportion of O2 and Ar will lead to an distinguished increase in the short circuit photocurrent of the n ZnO/p Si heterostructure, on the other hand, it shows very little effect on open circuit photovoltage. Even if the ZnO film have been doped with n type impurity dopants, the photoelectric translating efficiency of the ZnO film will reveal a sensitivity to the change of the O2 and Ar proportion. Also, we have proved that this phenomenon is the final result of the deviation of the O2 and Ar proportion in the DC reactive sputtering process, which consequently causes a change in the concentration of the n-type carrier(electron) and the short circuit photocurrent of the n-ZnO/p-Si heterostructure. Finally, we found that the photovoltage translating efficiency reaches its maximum value when the proportion of O2 and Ar is about 5:3.关键词：ZnO films;heterostructure;intrinsic defects;photoelectric translation84|113|0更新时间：2020-08-11
- 摘要：Materials with high phase velocity are required to achieve high frequency surface acoustic wave devices. Diamond can be considered as the utmost material when it is coupled with piezoelectric materials such as ZnO. ZnO/diamond/Si structures have exhibited a phase velocity as large as 10 km/s, which enables one to develop a high frequency SAW device without requiring high resolution lithography technologies.In this paper, the piezoelectric characteristic of ZnO multi layer and the potential application for SAW device with ZnO/diamond/Si film are studied. Firstly, ZnO films have been deposited on diamond/Si substrate by plasma-assisted metal-organic chemical vapour deposition (MOCVD). The characteristic of the films is optimized through two-step growth method. X-ray diffraction (XRD) spectra show that the as-prepared ZnO films are strongly c-axis oriented. Photoluminescence (PL) spectra exhibit an intensive ultraviolet emission peak for our samples, while the emission band for deep energy level transition disappears. Scanning probe microscopy (SPM) measurement is also used to analyze the surface roughness of the grown ZnO/diamond/Si films, the sample with lower roughness will reduce the surface influence on SAW device application. To investigate the SAW properties of the ZnO multi-layer structure approximatively, the theoretic frequency dispersion curves of SAW for ZnO material on different substrates are studied. The thickness of ZnO film has obvious effect on the working frequency of SAW devices,i.e., the thinner the ZnO film, the higher the phase velocity of the SAW for our material. And the center frequency of ZnO SAW devices on diamond/Si substrate is about two times of that of ZnO materials on other substrates. So the ZnO/diamond/Si multi-layer is promising to fabricate high frequency SAW filter.关键词：MOCVD;SAWF;XRD;SPM88|129|4更新时间：2020-08-11
- 摘要：ZnO is a wide band gap semiconductor with 3.36eV at room temperature. It has been studied for decades for its many applications, such as surface acoustic waveguide, transparent electrodes for some solar cells and buffer layer for epitaxy of GaN. In recent years, ZnO film attracted more attention due to its applications in photoelectric materials. It has been found to be possibly used in ultraviolet laser devices due to its ability to emit stimu lated ultraviolet photons. The shorter wavelength laser devices can provide many new applications. In order to fabricate photo electronic diodes, research on the electrical properties is now urgently needed. Using the method of Hall effect experiment, we can get some information on the semiconductor, such as the carrier concentration, conductance and transfer rate. For the sample of films, Van der Pauw method is very useful. It can be applied to measure the samples with anomaly geometry. But there were few detailed reports on the measu ring of ZnO films by using this method. Using Van der Pauw method to measure the ZnO films, the first problem is to prepare electrode, which is ohmic contact with ZnO films. Al is mostly used as ohmic electrode, but we found another Ag alloy material with lower contact resistance, which is better as ohmic electrode than Al. Second, it is stable at low temperature(77K),but Al is not. The last, the Ag alloy electrode is much easier to prepare. Using the Ag alloy as the ohmic contact, we get the carrier concentration of the sputtered ZnO prepared on glass substrate at room temperature to be 1.04×1017cm-3; the resistivity of 2.25Ω·cm and the transfer rate of 26.7cm2/V·s. We also get the temperature dependence of DC resistivity of the sputtered ZnO films. At high temperature (>280K), σ formally obeys the following formula: σ=σ0exp(-Ea/KT) where σ0 is a pre exponential factor, Ea the activation energy for band conduction, and K the Boltzmanm constant. And we find the activation energy of sputtered ZnO is 0.035eV. At lower temperature(77～280K),the dependence is different from the normal semiconductor. It may be caused by the drift of the impurity ions in grain boundary barrier.关键词：Van der Pauw;ZnO film;ohmic contact;Hall effect85|120|0更新时间：2020-08-11
- 摘要：Field emissive display (FED) is a newly developed flat panel display, the phosphors in which are excited by low voltage cathode rays. It is expected that this display would replace the widely used cathode ray tube (CRT) in near future. Y2SiO5:Ce is the important candidate blue phosphor for FED. The emission peak of this phosphor is at 410 nm, an eye insensitive wavelength. Questions appear: should this emission peak be moved to longer wavelength to increase the brightness of this phosphor? If this is the case, how does this moving affect the efficiency and the color triangle area of FED device? Chromaticity simulation was tried to answer the questions. The emission spectrum of the blue phosphor was simulated by using Gaussian function. The luminous efficiencies and color coordinates of Y2O3:Eu and Y3Al5Ol2:Tb were selected for red and green phosphors. During the calculations, these parameters were kept constant. The color temperature and the brightness of the display were set as 6500K and 300cd/m2, respectively, while the voltage of the electron beams was chosen as 2000V. It is also assumed that the brightness of the phosphors linearly increases with the current density of the electron beams. When the emission peak position and width of the blue phosphor were varied, the color coordinates and brightness efficiency of the blue phosphor were calculated. Furthermore, the brightness efficiency and the color triangle area of the display were calculated. During the calculation, adjusting the current densities of the electron beams to maintain the color temperature and brightness of the display. The decrease of the current density indicates the increase of the efficiency. The simulation gives following results: (1) Increasing the peak wavelength and width enhances the luminous efficiency of the blue phosphor, but reduces the color saturation of it, but if the peak wavelength is kept shorter than 460nm, the color saturation is acceptable for the display. (2) It is better to keep the peak wavelength of the blue phosphor in the range 420～460nm, in which the phosphor possesses saturated blue color; the color triangle shows large area and the display performs high efficiency. (3) The wavelength of Y2SiO5:Ce is too short for the display applications. If the wavelength could be shifted to longer wavelength, 20～40nm, it would be beneficial to improve FED performance. In some extent, the results obtained in the present simulation are also suitable to other color displays.关键词：FED;efficiency;chromaticity simulation73|73|1更新时间：2020-08-11
- 摘要：The eye-protection glasses against YAG laser disservice based on the bandgap reflection of one-dimensional photonic crystal is designed and manufactured. The light with wavelength of 1.06μm is reflected by the bandgap of one-dimensional photonic crystal (with the transmission below 10-7) and absorbed by the phosphatic glass substrate (with the transmission of 1%). It makes the glasses to be enough to protect the eyes from the disservice by ns-YAG laser with power energy of 1J/cm2 for all incident angle. The glasses have the transmission beyond 70% for the visible lights, and avoid the second disservice to others by the reflected light from the glasses. The testing data of the eye-protection glasses agree well with theoretical calculations.关键词：one-dimensional crystal;phosphatic glass;eye protected mirror;YAG laser101|85|1更新时间：2020-08-11
- 摘要：Red organic light emitting diodes (OLEDs) emitted from europium (Eu) complex have been fabricated. To get high purity characteristic emissiom from Eu-complex,2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was introduced as hole blocking layer. By introducing an alternate multilayer of 4, 4′-bis[N-(p-tolyl)-N-phenyl amino]biphenyl (TPD) /1,3,5-tris-(3-methylphenylphenylamino) triphenylamine (m-MTDATA) as hole-transporting layer which can confines the surplus holes injected from the ITO anode, compared with the conventional heterostructure device, the luminous efficiency and the maximum brightness can be improved significantly, the maximum luminous efficiency and the maximum brightness of the red EL emission are 3 cd/A at the current density of 2.8mA/cm2 and 670cd/m2 at the current density of 170mA/cm2, respectively. The mechanism to improve the red device performance with Eu-complex by the AM hole-transporting layer and effect of BCP on the emission characte ristic of the devices were also discussed.关键词：OLED;alternate multilayer;europium complex99|89|1更新时间：2020-08-11
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