最新刊期
卷 23 ， 期 4 ， 2002
- 摘要：Over past twenty years our research work is concentrated at photoelectronics and luminescence in wide band gap Ⅱ-Ⅵ compound semiconductors and its low dimentional structure. The main research results can be concluded as follows:The first, free exciton emission under excitation of electric field was systematically studied. Free exciton emission and its longitudinal optical (LO) phonon replicas in ZnSe and CdS MIS diodes have been identified in terms of Gross's theory. Pure green, blue, blue-violet and violet electroluminescence(EL) at room temperature(RT) have been obtained in Ⅱ-Ⅵ compound MIS diodes, respectively. The origin of two blue EL bands at RT in ZnSe MIS diodes is attributed to emission related to free exciton. The homogeneity of blue EL in ZnSe MIS diodes has been improved by using a suitable insulating layer. The second, optical bistatility (OB) in ZnSe-based multiple quantum wells (MQWs)was studied. ZnSe-based MQWs with high quality were fabricated by LP/AP MOCVD and identified by XRD, PL and SEM measurements. The OB with ns response was observed in ZnSe-ZnS MQWs at 77K for the first time. The origin of the OB is attributed to the dispersive nonlinearity due to the effect of excitonic saturating absorption. The OB with ps response was observed in ZnTe-ZnSe MQWs and ZnTe-ZnS MQWs at RT for the first time. The mechanism of the OB is attributed to increasing absorption effects due to the band gap shrinkage of the MQWs in high density photo-excitation. The OB in ZnSe-ZnS MQWs optical waveguide is also observed at RT for the first time, the switching response time of the OB is about 500ps and the threshold switching power is 1μW, which is much lower than that reported before. The third, the spontaneous and stimulated emission in ZnSe-based MQWs was studied. For Zn0.8Cd0.2Se-ZnSe MQWs four bands from PL spectrum were observed at 17K, and can be attributed to the n=1,2hh and 1h exciton transition, respectively. The stimulated emission from the cleaved edge of the sample with different cavity length were observed at 77K. It is noticed that the sample with shorter Fabry-Perot cavity length has the larger threshold excitation and more mode spacing. For ZnSe-ZnS MQWs the stimulated emission is observed and attributed to the exciton-exciton interactions. The elastic properties and related effects of the elastic strain from ZnSe-ZnSeS strained layer superlattice (SLS) have been studied by means of Brillouin spectroscopy. The longitudinal optical phonon modes LOm both in ZnSe well and ZnS barrier on ZnSe-ZnS SLS are observed by means of Raman scattering spectra. The fourth, the ZnCdSe-ZnSe ADQWs samples studied were grown on GaAs(100) substrate by LP-MOCVD at 350℃. The spontaneous emission in the sample has been studied. The exciton emission both in the narrow well(NW) and in the wide well(WW) is influenced by two factors:the exciton tunneling and thermal dissociation processes. For the NW the two factors have the same influence on emission intensity, but for the WW the influence are contrary. The change of the emission intensity in the WW is determined by the stronger one. The stimulated emission in the sample has also been studied. The carrier tunneling through the thin barrier is conductive to the stimulated emission from the WW, and the threshold can be lowered by optimizing the structure. The fifth, CdSe self-assembled quantum dots (SAQDs) were grown under S-K mode by LP-MOCVD. The formationprocesses of CdS SAQDs below the critical thickness was observed by atomic force microscopy (AFM) for the first time. It revealed that the formation mechanism of CdSe SAQDs under critical thickness was due to the effect of surface diffusion and strain release. Our results make it possible to observe the process of release strain directly. ZnSe1-xSx QDs were also grown under V-W mode by LP-MOCVD. The formation process of the QDs was studied by the surface morphologies and PL measurements. The sixth, growth and ultraviolet(UV) emission of ZnO thin film. ZnO thin films on Si substrate were fabricated by PECVD and thermal oxi关键词：Ⅱ-Ⅵ semiconductor;low dimension structure;optical properties85|103|3更新时间：2020-08-11
- 摘要：Optoelectronic integrated circuits and photonic integrated circuits on silicon substrate will meet the needs of information transmission and processing in the future. ZnSe are semiconductor materials with wide direct bandgap (2.7eV) at room temperature and have a high potential for realizing blue light emitting devices for optoelectronic/integrated optics applications as well as fundamental studies.High quality ZnSe epilayers on Si(111) substrate were obtained at 300℃ by LP-MOCVD, in which hydrogen selenium(H2Se) and dimethylzinc (DMZn) were used as the reactants. The pretreatment of the Si substrates was divided into two parts. The first part was a degreasing process, the second step is the etching procedure. ZnSe epilayer characteristics were investigated by X-ray diffraction, scanning electron microscope energy dispersive spectrometer (SEMEDS) and photoluminescence (PL). A single intense diffraction line of the ZnSe crystal was observed, confirming that the epitaxial layer was a (111)-oriented single crystalline layer. The EDS analysis on a SEM of the ZnSe epilayer on Si showed that there were only three elements including zinc, selenium and silicon. This indicated there is no significant impurities in the epilayer. In addition, the atomic ratio of Zn/Se was close to 1, the ZnSe epilayers had good stoichiometry. For the growth at 300℃ with H2Se flow rate fixed as 20mL/min, and a total H2 flow of 3OOOmL/min under a reaction pressure of 10.1×103Pa, the growth rates were determined by variation of DMZn flow rate. The growth rate increased significantly with the DMZn flow rate increasing from 3mL/min to 10mL/min. While the DMZn flow rate was fixed at 5mL/min, the H2Se flow rate incressed from 5mL/min to 20mL/ min, the grow rate had no significantly change. The results indicated that DMZn flow rate predominately controled the growth rate of ZnSe epilayer in this work.A strong blue near band gap photoluminescence(PL) peak around 447nm was observed at 77K without any additional PL signal at longer wavelengths. This indicates the absence of deep trapping centers. This peak shifts to around 465nm at room temperature, reflecting the decrease of the band gap with increasing the temperature. The presence of this intrinsic near band gap emission line in the PL spectrum even at room temperature is a further indication for the high quality of the ZnSe epitaxial layer. On the basis of the observed ZnSe/Si epitaxial film properties, the material has potential for optoelectronic integrated circuits and photonic integrated circuits.关键词：ZnSe epilayer;Si substrate;LP-MOCVD99|78|1更新时间：2020-08-11
- 摘要：We report the polarized optical absorption and photoluminescence spectra of single-walled 0.4nm carbon nanotubes (SWNTs) arrayed in the channels of an AlPO4-5(AFI)single crystal. When the light electric field(E) is polarized parallel to the tube direction(c), the absorption spectrum display a sharp peak at 1.37eV with two broad bands at 2.1eV and 3.1eV.The intensities of these absorption bands gradually decrease as the polarization angle is varied from 0°(E||c) to 90°(E⊥c).In the E⊥c configuration, the tube is nearly transparent in the measured energy region of 0.5~4.1eV. The photoluminescence observed around 700nm also shows strong polarization dependence. Under high power excitation using the fundamental frequency of a YAG laser, the sample shows strong nonlinear up-conversion emission around 700nm and high efficient second-harmonic generation. The mechanism of the nonlinear photoluminescence and SHG is not clear yet.关键词：single-walled carbon nanotubes;optical properties;polarized absorption;photoluminescence101|89|1更新时间：2020-08-11
- 摘要：It is shown in this paper that the mass difiference between ions of the host crystal has an effect on the thermal broadening and shift of spectral lines of active ions in the crystals. The effect is expressed as a multiplied factor D2 for the thermal broadening and shift caused by one-phonon absorption and emission mechanism, and a multiplied factor D4 for the thermal broadening caused by Raman scattering process. The expressions of D-factor are given for crystals constituted of two and three kinds of ions, respectively. Obviously, the factor of D equals to 1 when all of the ions in a crystal have the same mass, and it increases with the mass difference between different kinds of ions in the crystal. Therefore, when the other conditions are invariable, the thermal broadening and shift of the lines increase with the mass difference between ions. The values of D are given for two examples.关键词：broadening of spectral lines;shift of spectral lines;phonon;mass difference116|96|0更新时间：2020-08-11
- 摘要：Recently attention is focused on the quasi-phase-matched self-frequency-conversion (SFC) laser generations in rare-earth doped optical superlattice crystals, mainly because of their ability to generate multicolor lasers across the visible portion of the spectrum through a single crystal. We present a general model for quasi-phase-matched SFC lasers in rare-earth doped optical superlattice crystals by combining quasi-phase-matching (QPM) theory and the self-sum-frequency mixing (or self-frequency-doubling) laser patterns. The new model takes into account the TEM00 distribution of Gaussian beams with loose focusing, absorption and coupling of pump beams, and effects of imperfect periodical structures. Two types of errors:(1) random period errors and (2) linearly tapered period errors in the periodicity of these structures are analyzed to find their effects on the value of equivalent effective nonlinear coefficient and on the tuning curves of normalized conversion efficiency. Finally the model is applied to simulate the SFC laser properties in a Nd3+ doped aperiodically poled lithium niobate crystal. The calculated results, especially the threshold, the total visible laser output power and spectrum of relative laser intensity in the visible, agree well with the experiment, which indicates the validity of this model. Most significantly, the model presented explains and verifies the simultaneous laser generation of multiple visible wavelengths (686,605,542,482,441 and 372nm) from a single crystal.关键词：self-frequency-conversion laser;optical superlattice crystal;rare earth111|61|0更新时间：2020-08-11
- 摘要：With the development of solid science theory and experimental technology, the properties of surface magnetopolaron in crystals have been of considerable interest. Many investigators studied the properties of surface magnetopolaron by means of various theoretical methods. Larsen proposed a novel fourth-order perturbation method to investigate the properties of 2D magnetopolaron. Wei and co-workers calculated the induced potential and the self-energy of an interface magnetopolaron interacting with bulk LO phonons as well as interface-optical phonons using the Green-function method. The properties of surface magnetopolaron in semiconductor CdF2 and CdTe were investigated by means of a linear combination operator and a perturbation method by one of the authors.Most polar crystals are diatomic and cubic and their crystal structure belongs to NaCl, CsCl or ZnS type. In these crystals there is one mode of the longitudinal optical(LO) phonon. The properties of crystals have been studied by a great variety of techniques, in the case, of crystals having only one LO phonon branch. However, a large number of polar crystals, with several atoms per unit cell, have more than one LO phonon branch. For example, in cuprite such as CuO2, GaAs1-xPx and a large number of perovskites (SrTiO3,BaTiO3, LiNbO3) there are more than two modes. In recent years, the problem with many LO phonon branches has been investigated. The ground state energy of surface magnetopolaron in polyatomic polar crystals are calculated using linear combination operator method by one of the authors.In the early 1970s, Huybrechts investigated the internal excited state of the bulk optical polaron by using linear combination operator method. Gu et al. apply the Larsen method to investigate the properties of the ground-and excited-state energies of a magnetopolaron in a quantum well and in a slab of polar crystal. Kandemir et al. discussed the ground-state and first-excited state energy of two-dimensional large magnetopolaron by using recently introduced squeezed Landau states. The energy of the first internal excited state of the magnetopolaron were calculated by using linear combination operator method by one of the authors. However, the internal excited state of surface magnetopolaron in polyatomic polar crystals has not been investigated so far. In this paper, the properties of internal excited state of the surface magnetopolaron in polyatomic polar crystals are studied by using linear combination operator and unitary transformation methods.The results show that in a strong magnetic field the ground state energy E0, the first internal excited state energy E1 and the excited energy △E for the strong-coupling surface magnetopolaron in polyatomic polar crystals increases with increasing magnetic field B, whereas for the weak magnetic field the ground state energy, the first internal excited energy and the excited energy contain an extra contribution due to crossed terms between the different phonon branches.关键词：polyatomic polar crystals;surface magnetopolaron;internal excited state87|81|0更新时间：2020-08-11
- 摘要：Five GaN films grown by metal-organic chemical vapor deposition (MOCVD) method were investigated. The growth was performed using a home-made vertical reactor operating at atmospheric pressure. The growth was carried out on (0001) oriented sapphire substrates using trimethylgallium(TMGa) and blue-ammonia(NH3) as Ga and N sources, respectively. The mixed gases of hydrogen and nitrogen were used as the carrier gases. A thin buffer layer with thickness of about 15nm was grown at 520℃ and recrystallized at 1060℃ for 6 minutes. The GaN films were grown at 1060℃.Optical transmission measurement, photoluminescence (PL), double-crystal X-ray diffraction (DCXRD) and the Van der Pauw Hallmethod were used to measure the optical, structural and electrical data of these films at room temperature.Table 1 gives the characterization data of the five GaN films.Fig. 2 shows the optical transmission spectra of GaN films. The optical absorption edge of GaN films is at 366nm.The transmittance varies between 63% and 93% for the used samples.Fig. 3 shows the relationship between the FWHM of double-crystal X-ray diffraction (DCXRD) and transmittance. As shown in Table 1, the FWHM of DCXRD becomes smaller when transmittance increases, which suggests that the higher the transmittance, the better the crystal quality.Fig. 4 shows the photoluminescence (PL) spectra of five GaN films at 300K. The excitation-source was a 15mW He-Cd laser. The peaks of band-edge emission of Samples B, D and E were very sharp. The band-edge emission intensity of Sample A was very weak, but its FWHM of DCXRD was the smallest, which indicates that the optical property of GaN determined by PL isn' t in correspondence with the crystal quality determined by DCXRD.The experimental results show that the crystalline quality of GaN determined by transmission measurement is in agreement with that determined by DCXRD. But we did not observe the same relationship in PL spectra with DCXRD. This paper also reports that a highly resistive GaN film grown by atmospheric pressure MOCVD has RBS/channeling yield xmin of 1.5%.关键词：GaN;MOCVD;optical transmission spectra;double crystal X-ray diffraction;photoluminescence;RBS/channeling114|60|0更新时间：2020-08-11
- 摘要：Two kinds of blue OLEDs with the structure ITO/CuPc/NPB/JBEM:perylene/Alq/Mg:Ag [Device(J)] and ITO/CuPc/NPB/DPVBi:perylene/Alq/Mg:Ag[Device(D)] were studied.The maximum luminance were 7526cd/m2 and 6123cd/m2, maximum luminous efficiency were 1.45lm/W and 0.831m/W for Device(J) and Device(D), respectively. The difference of luminance and efficiency was not obvious for the two devices. However, there was remarkable difference for their lifetime. The Device(J) achieved the longer halflife of 1035h at initial luminance of 100cd/m2, and that of Device(D) was only 255h. According to their energy level diagrams, the difference of stability may originate from light emitting materials in the two devices. It may be attributed to the higher thermal stability of JBEM molecules than that of DPVBi. JBEM may be a promising blue organic light emitting materials.关键词：blue organic light emitting materials;stability124|91|2更新时间：2020-08-11
- 摘要：Solid-state green light sources are desirable for high density optical storage, color displays, optoelectronics and medical diagnositics. So far, the conversion of infrared into visible has been extensively studied on various crystals. As one of rare earth ions that:emit up-conversion fluorescence, erbium gives rather high efficiency and is studied widely as an active ion. Preparation and luminescence properties of rare-earth oxides nanocrystals have been extensively studied. However, up to now, fewer articles have been reported about rare-earth fluoride nanocrystals. In this report, fabrication of rare-earth fluoride nanocrytals YF3:Er3+ is reported in details. Based on the rare-earth oxides nanocrystals obtained by combustion synthesis, the YF3:Er3+ nanocrytals were prepared through fluoridizing reaction at 400℃. The samples were characterized by XRD. Under the LD excitation (λ=980 nm), the sample presents up-conversion luminescence with an intense green emission peaked at 547nm which belongs to the transition from 4S3/2→4I15/2 of Er ion and a week red emission peaked at 660nm from 4F9/2→4I5/2 transition. The green emission prevails over the red one due to the lower doping concentration and the lower phonon energy.关键词：rare earth fluoride;preparation;up-conversion luminescence93|62|2更新时间：2020-08-11
- 摘要：Mn doped ZnS nanoparticles have been extensively studied from the viewpoint of quantum size effects and the luminescent efficiency. In recent years, high luminescent efficiency association with particle size has been observed in Mn doped ZnS nanoparticles. In this article, a novel chemical method was developed to produce size monodisperse, highly luminescent, organic-monolayer passivated Mn doped ZnS nano-powder. The prepared particles are as small as 1.8~2nm, capped or modified by methacrylate polymer, their thermal, mechanical, chemical stability, durability, lifetime and luminescent intensity were greatly improved. The methacrylate polymer binds to the ZnS:Mn nanocrystalline surface through the physical absorption and provides steric stabilization through the hydrocarbon chain. The particle sizes can be easily controlled by the lengths of the polymer, which can be realized by changing the mole ratio of monomer to chain-transfer agent. The photoluminescence (PL) spectra of the ZnS:Mn nanopowder exhibit a slight red shift in optical properties. The enhanced PL intensity was explained by the nanosize effect. Transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and photoluminescence (PL) are used to characterize the structure of ZnS:Mn nanopowder. The size of the particles determined from XRD line broadening did not particularly differ from the results of TEM. The novel chemical method can be extensible to synthesize other kinds of metal doped nanopowders, and can also be extensible to prepare nearly monodispersivity Ⅱ-Ⅵ semiconductor nanopowders only need to select suitable material.关键词：ZnS:Mn;nanophosphor powder;synthesis133|118|2更新时间：2020-08-11
- 摘要：In the past decade, preparation of nanoparticles whose sizes and size distribution can be well controlled has become an important subject in materials science fields. Many methods have been developed in preparation of semiconductor nanoparticles, such as Langmuir-Blodgett (LB) films, colloid-chemical, electrochemical, electrophoresis, thermolysis of organometallic compounds in solution, template and self-assembled monolayers etc. The self-assembled monolayer was reported by Sagtiv in 1983. Hereafter the method has attracted wide interesting due to its simple operation, easy preparation, and no need of complex instruments, but it meets great difficulties to obtain a desirable size distribution.A new method for preparation of nearly monodisperse CdS nanoparticles by self-assembled monolayers of mercaptoacetic acid and oxalic acid is reported. The mercaptoacetic acid plays an important role in the formation of the CdS nanoparticles. The preparation procedures were shown in Fig. 1. There include three major steps:First, preparing of self-assembled monolayers of mercaptoacetic acid and oxalic acid on aluminum substrate; Second, immersing the substrate into solution containing Cd2+ to exchange ions; Third, Cd2+ reaction with H2S gas to form CdS nanoparticles. In the formation process of the nanoparticles, CdS molecular formed at mercaptoacetic acid will play a role of nuclear center. The CdS nanoparticles were characterized by SEM, XRD, XPS and PL, respectively. SEM image indicates that the average size is about 45nm, which is well agreement with XRD result. Room temperature PL spectrum shows that CdS has a wide emission band in the range from 500 to 800nm about and the emission peak is at 675nm, which is attributed to surface defects.关键词：self-assembled monolayer;CdS nanoparticles;nuclear center129|101|1更新时间：2020-08-11
- 摘要：In the past, for the effects of doping content on the properties of materials and the optimum doping content problems, research workers only do experiments according to experiences, then give out some qualitative explanations, and there never quantitative calculation has been reported. In this paper, a theoretical model is investigated and the expression of optimum doping content is proposed. Starting from crystal structure, a theoretical expression of the relationship among the optimum doping content and the crystal structure coordination number and preparation methods has been set up.Assumption 1:If a doping atom replaces a lattice atom, and there is another doping atom in the near lattices, two such atoms meeting results in impurity bunching.Assumption 2:The atom energy change for different film preparation process can be divided as follows:For sol-gel method or reactive evaporation method, △E≈0. For magnetron sputtering method, △E≈(1/2)kT. For vacuum evaporation method, △E≈kT. For CVD method, △E≈(3/2)kT.The experimental data fits a parabola equation as:P=P0x(1-x Z+1/2 e△E/kT)The optimum value of doping content is xOPT=1/(Z+1)ei,#em/em#=0,1/2,1,3/2,So according to the equality, we can calculate the optimum doping content in consideration of crystal structure and preparation methods.Using this expression, the optimum doping content of manganese-doped zinc sulfide nanocrystals can be calculated respectively. The typical values of quantitative calculation is:xopt≈5.88at%~7.69at%. Those values are just around 4at%~7at% and they are in accordance with the experimental results of Ref. [2]. The quantitative calculation results are in accordance with the experimental results. The author have been applied this method to calculate the optimum doping content of some other films successfully, such as some oxide semiconductor transparent conductive films, gas sensitive films, electrochromic films, ferroelectric films. The values are also in accordance with experimental results. Those results are reported in other papers latterly.The theoretical investigation in this paper may be shallow indeed and the results may be discreditable, but that calculation results are in accordance with experimental results may not be occasionally. The problem of optimum doping content must imply some rules undiscovered. We expect that this paper will be paid attention to, thus real theory of optimum doping content will rise as quickly as possible.关键词：ZnS;nonocrystals;optimum doping content;theoretical calculation105|95|1更新时间：2020-08-11
- 摘要：Semiconductor light-emitting materials are very important to visible displaying devices and to optoelectronics. In view of that silicon is a nonfungible semiconductor microelectronics material due to its excellent quality and low cost, therefore in the field of optoelectronics, people have long been looking forward to the realization of Si-based integrated optoelectronics by taking advantage of Si planar technique. The Si-based light emitting materials doped by rare-earth have received increasing attention in recent years. As for the rare-earth doped materials, neodymium (Nd3+) ion is a very versatile active ion which is widely used in laser crystal and fluoride glass due to the capabilities for the integrated optoelectronics.We reported the optical properties of Nd-incorporated into crystalline silicon by MEVVA (Metal Vapor Vacuum Arc) ion source implantation. In our work, the doses of the Nd ion were 8×1016, 1×1017, 3×17cm-2, respectively. The low Nd ion flux (~4.5μA·cm-2) was employed in case of the increasing of the target temperature during the implantation. The samples were subsequently treated by rapid thermal annealing (RTA) at 700,800,900 and 1000℃ for 20s under ambient nitrogen gas. Comprehensive analysis including scanning electron microscope (SEM) and X-ray diffraction (XRD) indicated that the morphology and the structure of the samples were closely relative to the dose of implantation and the temperature of rapid thermal annealing, and NdSi was formed under the annealed temperature of 1000℃. The blue light band (410~430nm) and red light band (746nm) photoluminescence were observed under the excitation of 254nm (~5.0eV), the intensity of those light emission gradually ascended with increasing the annealing temperature. The red emission (~746nm) is related to the intra-4f shell of Nd3+ radiation transition (4F7/2, 4S3/2→4I9/2). the correlation of the photoluminescence and the structure are also discussed.关键词：ion implantation;Nd3+;structure;photoluminescence111|75|1更新时间：2020-08-11
- 摘要：Sr2CeO4 with one-dimension structure is a new kind of material. The special structure leads to its photoluminescence properties. From JCPDS, Sr2CeO4 was in the triclinic crystal system with cell parameters a=6.070Å, 6=8.976Å, c=10.598Å, a=94.7°,β=90.4°, γ=95.8°. But it was reported recently that Sr2CeO4 was orthorhombic cell with a=6.11897Å, b=10.3495Å, c=3.5970Å. This was maybe caused that some key weak reflections were omitted. Sr2CeO4 structure consists of linear chains of edge-sharing CeO6 octahedra that run parallel to the [001] crystallo-graphic direction with a repeat distance of 3.597Å. There are two kinds of Ce-O bonds in the structure Ce-O and Ce-O-Ce, and the bond length of the former is 0.1A shorter then that of the latter. When Sr2CeO4 is excited at 310nm, the process of energy transfer may carry throng successfully because Ce-O bond is shorter than Ce-O-Ce bond, so strong fluorescence caused by charge transfer can be observed. M2CeO4(M=Ca, Sr, Ba) were prepared, and it was found that Ba2CeO4 which has a similar structure with Sr2CeO4 can emit fluorescence, but Ca2CeO4 which has a different structure can't emit fluorescence. The fluorescence of Ba2CeO4 is weak, which is caused by the larger Ba2+ radium leading to lattice expanding and making energy transfer difficult. Ca2CeO4 has a different structure, that is to say, there is no one-dimension chain in the structure of Ca2CeO4 and no energy transfer, so that the fluorescence of Ca2CeO4 can't be observed. The characteristics of one-dimension structure compounds can be summarized:(1) A shorter M-O bond in the one-dimension structure may lead to fluorescence caused by charge transfer.(2) M has alterable valence, and in the one-dimension structure M has a higher valence and the lower valence M can emit fluorescence.(3) The emitting band and exciting band are always broad, which is in favor of making use of energy.(4) The fluorescence caused by charge transfer is easy in one-dimension structure, which leads to the fluorescence of some compounds that can't emit fluorescence in other structures.关键词：Sr2CeO4;one-dimension structure;photoluminescence properties90|57|3更新时间：2020-08-11
- 摘要：The influence of different annealing atmospheres (vacuum, air, reductive) on the luminescent properties of lead tungstate single crystals (PWO) has been investigated. UV-excited emission spectra and their excitation spectra of the same PWO sample at different annealing conditions were reported. The emission of PWO as grown was weak and dominated by the defect-related red band which is a disadvantage for the scintillation of PWO. The intrinsic blue band was just discernable from the red band. After air annealing, the luminescence intensity was increased enormously and the green band was turn into the prominence of the emission spectra. It suggested that the green emission originate from some local excess oxygen defects, such as (WO42-+Oi) centers (here Oi means interstitial oxygen atom). After subsequently vacuum annealing, the emission intensity was dropped again, and the increase of 420nm excitation in the excitation spectra of the red band emission was remarkable. The color center around 420nm is harmful to the radiation hardness of PWO and should be avoid. It suggested all the unfavorable factor after vacuum annealing is caused by the increase of the concentration of oxygen vacancy Vo since the oxygen in the lattice can diffuse outward through the surface when annealing in vacuum under high temperature. So air annealing which decrease the concentration of Vo is a good method to improve the luminescence properties in full scale.In addition, the splitting of 310nm excitation band into two sharp excitation peaks around 305nm and 320nm was observed for the first time when another PWO sample was investigated after vacuum annealing. With the increasing of Vo concentration, 305nm peak lowered while 320nm peak heightened. It suggested that 305nm excitation is corresponding to the excitation of intrinsic excitons while 320nm excitation is corresponding to the bound exciton related to Vo-defects.关键词：PbWO4 crystals;annealing atmosphere;lattice defects;oxygen vacancy Vo114|60|0更新时间：2020-08-11
- 摘要：ZnO thin film is a promising material for short-wave laser and LBD etc, due to its wide band gap (3.37eV) and high exciton binding energy (60meV) at room temperature. But its photoluminescent properties received little attention in the past years, because there was unavoidably more or less defection in this material produced by traditional methods. To solve this problem, its preparation techniques need to be further improved. In recent years, some new methods were introduced to produce ZnO thin film such as MOCVD, MBE and so on. ZnO becomes hotpoint in all kinds of researches, especially in designing optoelectronic devices. In our work, the ZnO thin films were deposited on quartz substrates by radio frequency magnetic sputtering. We reported the measurements of XRD patterns, absorption spectra and photoluminescent spectra of our samples at room temperature. We also discussed the effect caused by the change of the ratio of oxygen to argon on the qualities of thin films. The ratio of 20:70 was found optimal. From XRD patterns, we can see our samples have good crystalline. On the other hand, ZnO thin film showed strong absorption in the UV region. The photoluminescence was correspondingly strong UV emission peaked at 392nm. It is obvious that near band emission is dominant in various transitions. High structural perfection of our sample was shown in these figures. The state of abundant Zn in ZnO thin film was greatly improved.关键词：ZnO thin film;photoluminescence;sputtering80|94|6更新时间：2020-08-11
- 摘要：At room temperature, there are two emission peaks in the luminescence spectrum of LiBaF3:Eu2+ powder sample. One is a broad band peaked at 410nm, and the other one is a narrow band peaked at 360nm, corresponding to 5d-4f and 4f-4f transitions of Eu2+, respectively. Furthermore, taking the reflection spectrum of Au thin film as reference, the reflection spectra of LiBaF3:Eu2+ sample are measured in the range of 50~400nm at U10B station of the National Synchrotron Radiation Laboratory (NSRL). The absorption spectra are calculated from the reflection spectrum by using the Kramers-Kronig relation. It is found that the energy gap Eg of this material is about 12.1eV. We believe that in the absorption spectra of LiBaF3:Eu2+, the 53.4, 59.4, 65.3, 69.2 and 76.5nm sub-bands correspond to transitions between core levels of Ba2+5p and F-2p electrons, respectively. Then the 183.4nm sub-band is attributed to the intrinsic defects absorption.On the other hand, without the pre-irradiation, one can observe the luminescence of LiBaF3:Eu2+ powder sample under the excitation of wavelength longer than 450nm. It means that the LiBaF3:Eu2+ sample has the photo-stimulated character.关键词：vacuum ultra-violet spectra;photo-stimulated;synchrotron radiation;LiBaF3：Eu2+106|76|0更新时间：2020-08-11
- 摘要：GdVO4:RE3+ is a significant red-emitting material with a main emission peak at 619nm.The luminescence intensity of GdVO4:Eu3+ is in the same order as that of YVO4:Eu3+. GdVO4:Eu3+ has good temperature properties and higher quenching temperature than that of YVO4:Eu3+, so it is very suitable for application in high temperature environment such as high-pressure mercury-vapor lamps. Usually, there are so many defects and traps in solids. Thermoluminescence(TL) is a useful tool to provide us with the information of solid defects and traps. The thermoluminescence of GdVO4:Eu3+ range from 100K to 500K was detected. The sample was excited by X-ray at the temperature of 90K. The velocity of rising temperature is 0.5K/s. The result shows that there are three main TL bands peaked at 193, 253 and 304K. The trap parameters are obtained from the TL curves. The trap depth is 0.39, 0.47 and 0.61eV, respectively. The origination of traps has three possibilities. Firstly, the color centers such as F centers and F+ centers as a result of the volatilization of V2O5 during preparation can form trap level in the forbidden band. The second, when Eu3+ is doped into host and enter into Gd3+ sublattice, the distortion of the lattice also can form trap level. Finally, because the sample is powder, there is many surface states which can form traps, too. Above all, the most possible reason maybe the color centers.关键词：thermoluminescence;GdVO4：Eu3+;trap101|77|3更新时间：2020-08-11
- 摘要：Optical and color parameters are luminous flux, color coordinate, color temperature, color rendering index and light efficiency for white LED illumination light source. They depend mainly on materials of semiconductor and phosphor. Operation current and temperature also affect on them. The relation between operation current, temperature and optical and color parameters were researched in sphere and constant driving current source. Property of white LED by phosphor is better than that of tri-color white LED in light efficiency. It consists of part blue light and yellow or red green light produced by the phosphor under blue LED's excitation. With the increase of LED operation current, the temperature of LED also increases, wavelength of blue light moves to long wavelength. It does not match on exciting wavelength of phosphor. The luminous energy of yellow or red green light decreases in phosphor. The increase of temperature produced decrease of energy directly, simultaneity. Light efficiency of LED decreases. The LED color changes from white to blue. Color rendering index is bad. When operation current of LED is constant and the operation temperature increases from 20℃ to 130℃, the results are similar to that of above. In order to improve light efficiency of LED, current of 20mA and operation temperature less than 50℃ are better. 40~50mA current is also used in order to decrease number of LED and cost. Rendering index of white LED is about 80 because its red energy is less than sunlight. It can be improved to 93 by increasing the red light. The best approach is to improve red emission of the phosphor.关键词：white LED;illumination light source;rendering index;light efficiency140|105|9更新时间：2020-08-11
- 摘要：The PDP would be the most promising that panel displays for high definition television (HDTV), wall-hanging TV, because the size can be increased relatively easily and it also offers fast response, a wide viewing angle and other advantages. In PDPs, three primary color phosphors are excited by more energetic vacuum ultraviolet (VUV) radiation of wavelengths of 130, 147 and 172nm from inert gas plasma. PDP phosphors are exposed to the VUV of high energy and high intensity. Thus the radiation stability of phosphors should be considered seriously. The color center and surface defects of phosphor caused by the radiation will decrease luminescence efficiency. In the paper, the radiation properties of PDP phosphors were studied by 147nm excitation. These PDP phosphors are (Y, Gd)BO3:Eu(red), Zn2SiO4:Mn (green), (Ba, Sr) O·nAl2O3:Mn (green) and (Ba,Mg)O·nAl2O3:Eu2+(blue). We have observed the decay of (Y, Gd)BO3:Eu is the smallest amount the four phosphors; the decay of (Ba, Mg)O·nAl2O:Eu2+ is the fastest at the beginning, then the decay speed change slower. It may be the Eu2+ in (Ba, Mg)O·nAl2O3:Eu2+ is unstable, because it could be oxidized to Eu3+ under the VUV radiation. We have found that the brightness of Zn2SiO4:Mn(green) and (Ba, Sr)O·nAl2O3:Mn rise at first, then decay down; the decay of Zn2SiO4:Mn is slower than that of (Ba, Sr)O·nAlO3:Mn, but the brightness of (Ba, Sr)O· nAl2O3:Mn is higher than Zn2SiO4:Mn. The performance of the commercial PDP phosphors is still not good enough for practical application. For the wide spread acceptance of the PDP, new phosphors should be developed in the near future.关键词：phosphor;radiant properties;vacuum ultraviolet88|79|3更新时间：2020-08-11
- 摘要：Carbon naontubes(CNT) have excellent electron emission performance as field emission cathode (FEC). In this paper, the method of fabrication FEC with powder CNT, including of affixing, purifying and surface treating, has been reported. The major performance of the most concern are the uniformity of electron emission, current density and lifetime. The raw materials CNT were ground with little balls in alcohol suspension, then were dropped on metal substrate. After hydrogen plasma surface treatment, electron field emission properties of these CNT cathodes were studied using a diode structure with phosphor-coated ITO transparent anode. The results showed that the threshold field is less than 3V/μm; emission site density was about 104/cm2; the emission current density was 1mAl/cm2 at an electric field of 4.4V/μm and the lifetime was more than 800h.关键词：carbon nanotubes (CNT);field emission;lifetime87|117|2更新时间：2020-08-11
- 摘要：The mercury adsorbed and deposited on phosphor plays an important role in light reduction during fluorescent lamp operation. However the coating treatment for phosphor or coating a film on lamp tube may reduce the adsorption-deposition of mercury and then degradation of light efficiency. A method for the determination of mercury amount on phosphor by cold vapour atomic absorption spectrometry is proposed. The method is based on the absorption of mercury atoms at 254nm resonance line at room temperature. Such absorption is directly proportional to concentration of mercury vapour. In the experiments, mercury was reduced by adding the reducer to a series of standard solutions of mercury and was then blew into the light path of the mercury surveymeter. The calibration curve was obtained. At the same time, monochromatic fluorescent lamps were prepared by using blue emitting BAM phosphor and coated BAM phosphor with nano-scale Al2O3 film respectively. After different lighting times, the mercury contents of the phosphors were measured. The regression equation of the calibration curve was found to be Y= 0.4455X+0.2000. A linear relationship between the experimental signal and mercury content was attained when the mercury concentration was below 2.4×10-2μg/mL. The recovery was 92.3~99.8% for samples analyzed by standard additions method. Therefore the method was found to meet the demand for determination of mercury content on phosphor.It is proved that the mercury content adsorbed on blue emitted phosphor samples increases with lamp operation time and is accompanied by a decrease of the brightness. Therefore, the light reduction can be mainly attributed to the adsorption and deposition of mercury. Moreover, compared to the coated BAM phosphor by nano-scale Al2O3 film, the mercury content of uncoated phosphor was evidently larger. Thus, the coating treatment of the phosphor can protect the powder and reduce the adsorption-deposition of mercury. As a result, the degradation of light efficiency of the coated BAM phosphor is inhibited in the course of lighting.关键词：mercury;cold vapour atomic absorption spectrometry (CVAAS);phosphor;decreasing brightness80|98|0更新时间：2020-08-11
- Address：No.3888 Dong Nanhu Road, Changchun, Jilin, China Postal code：130033
- Tel：0431-86176862 Email：fgxbt@126.com
- Technical support is provided by Beijing Founder electronics co., LTD 吉ICP备11002662号-17
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0