最新刊期
卷 26 ， 期 6 ， 2005
- 摘要：Recently,there has been significant interest in studies of the localization of electrom agnetic waves (EW)in photonic band-gap(PBG)matcriale.The interest is partially due to the fact that the interactions between the electrons don't exist any longer and the experiments can be performed at the room temperature.Furthermore,the special property of the control of propagation of light in the PBG has patential applications in many potical devices.One or multiple applications in the fabrication of lasers,light-emitting diodes,and single or multiple channelde filters,and so on.On the other hand,optical response of nomal-mode coupling semiconductor microcavities have attracted special interests for researchers.Opticalm icrocavities can confine light to small volumes by resonant recirculation.Devices based on optical microcavities are already indispensable for a wide range of applications and studies such as light-emitting diodes with high-efficiency and good-quality,optical switches,logic gates,lasers,photolum inescence devices,photonic crystal waveguides and so on.We investigate the normal-mode coupling dispersive medium in a symmetric 1D PCs.We use oscillator model to simulate the linear susceptibility of the dispersive layer.Given a reduced oscillator HWHM linewidth and a reduced frequency of the oscillator resonance,the single longitudinal defect mode will be split into two transmission peaks due to a high dispersive absorption.It is found that the separation between the two transmission peaks enlarges with increasing the idmensionless coupling strength.That means we can modulate the frequency shift of the dispersive defect by adjusting the parameter of the dispersive medium.We have also calculated the relationship between NMC and the oscillator,detuning effect of the cavity.By introducing a concept of complex effective refractive index,we calculated the imaginary part of the complex effective refractive index.So we can give a clear physical picture on normal coupled modes in a symmetric one-dimensional photonic crystal.关键词：photonic crystals;dispersive media;complex effective refractive index;transmittance96|80|0更新时间：2020-08-11
- 摘要：With recent rapid development of epitaxial techniques such as molecular beam epitaxy(MBE) and metal organic chemical vapor deposition(MOCVD),there has been great interest in investigating quantum well and wires both in materical science and condensed state physics field.Due to the electron motion along the length of the wire is free size and is quantized in the two dimentions perpendicular to the wire in quantum wires,they had a series of new and serious special physical properties which are quite different from those of the semiconductor constituents.These had brought infinite chance and hope on development and use of new materials.Especially,electron in quantum wire was subject to a two-dimension confinement,so that quantum effect was quite different from those of the bulk metericals,these would brought about great society benefit and economic benefit.So many scientists have been investigating properties of quantum wires.Francisco has stu-died the hydrogenic impurity binding energy in QWWS;Chuu et al.have calculated the energies of the ground state and the excited state in cylindrical quantum wires using Pekar alternative approach and peturbration-variational approach.Zhou and Gu have discussed the properties of polaron and magetopolaron in cylindrical quantum wires and in rectangular quantum wires by using variational solutions and linear combination operators me-(thods.) Guo et al.have investigated the electron-optic effects of double-layered quantum wires in magnetic field by means of density-matrix treatment.In this paper,taking into account the interaction of the electron with optical phonon modes in parabolic quantum wires,we have investigated weak-coupling polaron effective mass and the mean number of optical phonon by using of Tokuda's improved linear combination operators,the Lagrange multiplier and the variational method.Numerical calculations,for the ZnScrystal as an example,are performed.The results indicated that,both the effective mass m* of polaron and the mean number of optical phonon Nincreased with the increasing of Lagrange multiplier u.With the increasing of confinement strength ω0 of quantum wire,vibration frequency λ of polaron would increase.In short,both the effective mass m* and the mean number of optical phonon Nof polaron increase with the increasing of Lagrange multiplier u as well as(vibration) frequency λ of polaron increase with increasing of confinement strength ω0 for weak-coupling in a parabolic quantum wire.关键词：parabolic quantum wire;polaron;effective mass;mean number of optical phonon;weak-coupling102|96|1更新时间：2020-08-11
- 摘要：The effect of the electron-phonon interaction on an electron bound to an impurity in a parabolic quantum well(PQW) has been studied theoretically in the past,but similar studies calculating the pola-rization potential in a PQW have not been reported.In this paper,the polarization potential and the binding energy of the bound polaron in the PQW are investigated.The study has taken the effect of bulk longitudinal optical(LO) phonons and the interface longitudinal optical(IO) phonons into account.By using the method of modified Lee-Low-Pines(LLP) variational method,the polarization potential and the binding energy of the bound polaron in the GaAs/AlxGa1-xAs PQW are obtained.The contribution of the impurity-phonon interaction to the total electron energy can be eliminated by the first canonical transformation,and the effect of this displacement on the lattice polarization leads to the polarization potential which partially compensates the electron-impurity Coulomb interaction.By the second canonical transformation,the ground state energy of the bound polaron in the infinite parabolic quantum well is worked out,and then the binding energy of the bound polaron can be gained by further calculations.The research results indicate that,the polarization potential is much smaller in the wider wells,but it is larger in the narrow wells,therefore,the polarization potential should not be neglected in the very narrow wells.For a given well width,the polarization potential decreases rapidly with increasing |z| and gets a minimum,then it increases with increasing |z| near the interface of the well.The contribution of the polarization potential to the ground state energy of the bound polaron decreases rapidly with increasing the well width(L) at first,and then decreases slowly with increasing L and approaches zero at large L.The binding energy of the bound polaron decreases rapidly with increasing L at the beginning,then decreases very slowly with increasing L and finally closes to the value of three-dimensional GaAs.In summary,the polarization potential should not be eliminated in a narrow PQW.关键词：parabolic quantum well;bound polaron;electron-phonon interaction96|127|0更新时间：2020-08-11
- 摘要：Since Esaki and Tsu composed semiconductor superlattice,the special properties of electron in superlattice and heterostructure have been investigated by many persons.Especially for cylindrical quantum wire,a lot of works have been done.The Hamiltonian for the electron-LO phonons interaction in cylindrical QW has been derived by Constantinou and Ridley following the calculation of continuum model.Using variational method,Zhou studied the size dependence of the ground state energy,excited energy and cyclotron resonance frequency of magnetopolaron in cylindrical QW.Considering the interaction of electron-SO phonons,Buonocore investigated the self-energy of polaron by using the transformation and the variational methods and also studied the ground state and the first excited state self-energy of magnetopolaron.Employing LLP mediate coupling method,Sheng investigated the self-energy and effective mass of polaron in which the interactions of electron-LO phonons have been taken into account.Hua studied the self-energy and effective mass of polaron by using LLP transformation and also using the variational methods,he investigated the relation between the ground state energy,the electron-SO phonons interact energy of excited state and cyclotron resonance frequency of magnetopolaron.Employing LLP variational approach and perturbation method,Xie studied the polaron effect in a freestanding quantum wire.Considering the interaction of electron-LO phonon,Ding studied the systematic ground state energy and the interact energy of electron-LO phonon.In this paper,the size dependence of the mean number of optical phonons of polaron in cylindrical quantum wire was investigated by using the LLP variational approach and taking into consideration of the electron-bulk LO phonon coupling.Numerical calculations are performed.The result illustrates that the mean number of bulk LO phonons of polaron N will decrease with the decreasing R(the radiu of cylindrical quantum wire's cross section) and it will increase with increasing coupling strength.The coupling strength will increase with decreasing R.关键词：mean number of optical phonon;cylindrical quantum wires;the radius of quantum wire's cross section120|114|2更新时间：2020-08-11
- 摘要：The group Ⅲ nitrides GaN AlN,InN and their ternary compounds display a promising potential for optoelectronics applications,particularly laser diodes emitting in blue and ultraviolet range.These materials are well suited to form semiconductor quantum well and superlattices in many optoelectroic devices.There is an increasing interest nowadays in the quantum wells generated by nitrides GaN AlN,In Nand their ternary compounds due to conspicuous device applications,such as high-brightness blue(or green) light emitting diodes and laser diodes.However,the properties of the nitride parabolic quantum well materials,to our knowledge,have rarely been investigated.The parabolic quantum well structure has been successfully fabricated by the molecular beam epitaxy growth method.There are two kinds of parabolic quantum well,one is compositional parabolic quantum well,and another is doping parabolic quantum well.Therefore,the research of the nitride parabolic quantum well materials is very needed.In this paper,the energy level of a hydrogenic impurity in GaN/AlxGa1-xN compositional parabolic quantum well was investigated by variational method.The ground state energy,the first excited state energy,the binding energy and the 1s→2p± transition energy of the hydrogenic impurity in a GaN/Al0.3Ga0.7N parabolic quantum well as functions of the well width Lare given.The numerical results indicated that the ground state energy,the first excited state energy,the binding energy and the 1s→2p± transition energy decrease with increasing well width L and finally closes to the corresponding values of 3D GaN.The bound degree of the GaN/Al0.3Ga0.7N parabolic quantum well to the hydrogenic impurity is stranger than that of the GaAs/Al0.3Ga0.7As parabolic quantum well.Therefore,the electron coupled to a hydrogenic impurity in the GaN/Al0.3Ga0.7N parabolic quantum well is stable than that in the GaAs/Al0.3Ga0.7As parabolic quantum well.关键词：nitride parabolic quantum well;hydrogenic impurity;binding energy116|90|1更新时间：2020-08-11
- 摘要：Emission spectra of Yb:YAG with Yb3+ doping level from 5% to 30% at room temperature and(97 K) were characterized by cathodoluminescence spectra and the results showed the strongest emission peak is at 335~350 nm at room temperature which attributes to charge transfer luminescence(CT→F7/2) and shifted to shorter wavelength with decreasing temperature.Scintillation properties of Yb:YAG with different Yb3+ doping level were studied by measuring relative light output and decay time of Yb:YAG crystal.Measurements of relative light output and temperature dependence have been performed with α excitations and the results showed light output is related to Yb3+ doping level and crystal quality and the maximum achieved at low temperature for 5% Yb:YAG.The decay time and temperature dependence were measured by 22Na excitation.The decay time of Yb:YAG crystal with different Yb3+ doping level at room temperature is less than 50ns and it is monotonically decreasing with increase of temperature above the temperature where maximum of light output achieved,and decay time is monotonically decreasing with decrease of temperature below that temperature.Quenching temperature of Yb:YAG crystal at which the emission intensity has dropped to half of its maximum was determined.The relative light output and quenching temperature of Yb:YAG crystal with different Yb3+ doping level are different.Relative light output decreases with the increase of Yb3+ concentrations,while quenching temperature increases with increase of Yb3+ concentration.5% Yb:YAG crystal has maximum relative light output and the lowest quenching temperature.We conclude from our measurements that Yb:YAG crystal should be possible for application in medical imaging at low temperature.关键词：Yb:YAG;scintillation properties;neutrino;light yield;concentration quenching138|117|5更新时间：2020-08-11
- 摘要：Some former researches revealed that the composition of Eu,Dy co-doped alkaline earth aluminate plays an important role on the persistent luminescence.However,the researches about the effect of composition on luminescence of phosphors was not systemically carried out up to now,and the relevant mechanisms were not clearly given out.In this paper,Eu,Dy co-doped strontium aluminate phosphors with different composition were synthesized by solid-state reaction,crystal phase composition of phosphors was investigated by XRD technology,emission and excitation spectra and afterglow decay curve were measured via fluorescent photometer.The influence of strontium aluminate composition on phosphorescent properties was studied.The results of XRD and persistent luminescent properties showed that three crystal phases(SrAl2O4:Eu2+,Dy3+;Sr4Al14O25:Eu2+,Dy3+ and SrAl4O7:Eu2+,Dy3+) with good persistent luminescent properties could be formed by changing Al2O3/SrO ratio.From excitation and emission spectra and afterglow decay properties,it can be concluded that with the decreasing of Sr/Al ratio,excitation spectra extend to short wavenumber side,emission peaks take blue-shift,initial afterglow luminance is increased and afterglow life is prolonged.The effect mechanisms were investigated and discussed.There are more O2- ions around the Eu2+ ions in Sr2+-poor phases so the effect of crystal field on electron levels of Eu2+ ions is bigger(maybe due to the high electro-negativity of oxygen),the electron levels are split more.It is this reason that makes emission peaks blue-shift.Thermoluminescence results showed there were bigger trap depth and higher trap density in Sr2+-poor phases so that the Sr2+-poor phosphors showed better persistent luminescence.关键词：phase composition;aluminate;luminescence;afterglow111|81|3更新时间：2020-08-11
- 摘要：ZnS series electrolum inescence have obtained extensive applications in low brightness illuminance,LCD,automobile and aircraft instrument etc.ZnSas electrolum inescence material is always doped with Mn and Cu.Mn2+ ions form luminescent center of orange color emission with wavelength about 580 nm in the crystal,Cu+ ions form not only luminescent center,but also CuxS which is indispensable to luminescence.Accordingly Mn and Cu have obvious influence on luminescence brightness.Due to the doping with more Mn in ZnS:Cu,Mn orange electroluminescence material,the excess of Mn will influence on internal structure of ZnS;and some else compounds of Mn would likely bring adverse influence on the brightness of electrolum inescent material in burn process,which induce the brightness of electrolum inescent material far lower than blue or green materials.In this paper,doping with proper compounds of Mn or Cu in annealing process,with the method of diffusion at low temperature,it make Mn2+ enter crystal lattice of ZnS evenly,and obtained ZnSCu Mn ACEL powder material with higher brightness.The influences of content of Cu and Mn,categories of compound of doping Mn,and annealing temperature on luminescence brightness were discussed.The experimental results showed that among three categories compound of Mn(carbonic acid manganese,acetic manganese,vitriol manganese),the material with acetic manganese as dopant exhibits the maximal brightness.Materials with highest brightness by this preparation were obtained at annealing temperature of 700℃ and doping dose of Mn(acetic manganese as dopant) at 2%,and Cu at 0.1%.The brightness of the material doped with Mn is twice as higher as that of general material annealing at low temperature.关键词：high brightness;orange;electroluminescence;ZnS140|74|4更新时间：2020-08-11
- 摘要：A model for inorganic semiconductor has been presented to calculate the J-V characteristics of organicelectroluminescent devices(OELDs).The additional dipole energy introduced by inserting a thin LiF layer at metal/organic interface significantly decreases the potential barrier for electrons injection and the turn-on voltage of OELD.The charge carriers injection has been balanced,and then the performance of OELD has been greatly enhanced.Bydetailed numerical calculation,it has been found that the optimal thickness of inserted LiFshould be in the range of 1.5~5.0 nm,too thick or too thin LiFwill increase the turn-on voltage of OELD and degrade its performance.It hasbeen proved that this model is proper to explain the performance enhancement of OELDs via modification of electrodewith LiF.关键词：OLEDs;electrode modification;interface dipole110|79|0更新时间：2020-08-11
- 摘要：The organic light-emitting diodes have been considered for applications in backlights of liquid-crystal displays,ultrathin plat full-color display,efficient illuminators and electro-pumped organic solid laser,etc.The process responsible for electroluminescence requires the injection of electrons from one electrode and holes from the other,the electron-hole pairs form excitons in emitting layer,and then the light generate through the radiative recombination of the excitons.In the past near upon twenty years,great progress has been made in electroluminescent devices and materials.Up to now,the three primary colors of red,green and blue,which are required for full-color displays,have been achieved.Among these,the green emission is the most perfect and the corresponding device almost reaches to commercial criterion.However,the blue and red emissions are more challenging,and there are many activities to be focused on efficient blue and red light-emitting materials.This paper reviews our recent works on blue organic light-emitting diodes,including blue materials,such as the metal chelate complex,(2,3-methyl-8-hydroxy-quinoline) lithium(LiMMq),and derivates of polyfluorene,dendritic polyfluorene(PDFA),and blue electroluminescent devices based on exciplex emission formed at the interface between9,9-Dibutyl-N,N,N',N'-tetraphenyl-9H-fluorene-2,7-diamine(DTFD) and 2,2-[1,2-phenylenebis(oxy)] bis(N,N'-diphenyl-acetamide)(PBD).The performances of the blue emitting materials and the devices have been studied by photoluminescent,electroluminrescent spectra and characteristic of current-brightness-bias voltage etc.The life-time and color-purity of blue organic light-emitting diodes are required to be further improved for the commercial production.关键词：organic light-emitting diodes;metal chelate complex;derivative of polyfluorene134|117|2更新时间：2020-08-11
- 摘要：As well-known,heteroepitaxial growth on sapphire is mainly employed to obtain optoelectronic devices because there is no suitable substrate matching with GaN.Therefore,the GaN layer suffers from a stress due to large difference in lattice constants and thermal expansion coefficients between the GaN and sapphire.To improve the quality of devices,the epitaxial lateral overgrowth(ELO) technique is applied to GaN.ELO-GaN on patterned SiO2/GaN/α-Al2O3 substrate is grown by metalorganic chemical vapor deposition(MOCVD).First,a high quality 3 μm thick layer of GaN is grown by MOCVD.Next,standard deposition and photolithographic techniques are employed to prepare a set of parallel SiO2 stripes oriented along a <1100> GaN crystal direction separated by window areas which expose the underlying GaN.Asecond deposition of GaN onto this patterned substrate is then initiated.During the initial GaN growth,the SiO2 stripes function as nonwettable surfaces and no GaN deposition occurs on them.However,once the GaN film growth from the window stripes reaches the tops of the SiO2 stripes,epitaxial lateral overgrowth of GaN commences.The GaN thickness of the second step growth is about 10 μm.The results of a systematic study of the ELO-GaN on sapphire are reported.Atomic force microscopy(AFM) images showed that the surface of ELO-GaN is smooth and that there are linear-configuration hillocks in the middle of mask region,which are caused by the misorientation of crystalline when the ELO-GaN coalesce above the masks.The X-ray diffraction(XRD) curve revealed that the tilts in the <1120> direction between GaN in window regions and mask regions are about 1.2°.Raman scattering spectrum revealed that the stress in the mask region is smaller than that in the window region and also the quality of GaN is much higher in the mask region.As a result,the quality of GaN crystalloid is effectively improved by MOCVD using the ELO technique.关键词：epitaxial lateral overgrowth;MOCVD;GaN;AFM;Raman scattering106|76|1更新时间：2020-08-11
- 摘要：The understanding of the temperature dependence of carrier dynamics in an asymmetric double-quantum-well is essentially important for the realization of room temperature efficient photonic devices.As the temperature increases,the carriers will be thermally evaporated into the barrier layer from quantum wells and then some of them will be recaptured by the quantum wells,i.e.carrier coupling takes place between the different quantum wells when the temperature increases.The ratio of photoluminescence intensity of different quantum wells can reflect the distribution of carriers in each well.The temperature dependence of the ratio of photoluminescence intensity in an asymmetric double-quantum-well has not been reported until now.The temperature dependence of the carrier coupling in an asymmetric double-quantum-well was simulated by using the coupling multiple-quantum-well model of carrier dynamics.It is shown that the ratio of photoluminescence intensity of each well strongly depends on the difference of thermal activation energies.The maximum of the ratio of photoluminescence intensity depends exponentially on the difference of thermal activation energy,while the temperature corresponding to the maximum depends linearly on the difference of thermal activation energies.This simulation method can be used to study carrier thermal escape and re-trapping in quantum-dot-quantum-well heterostructures formed by sub-monolayer deposition,which will be published in the near future.关键词：asymmetric double-quantum-well;ratio of photoluminescence intensity;thermal escape;re-trapping109|83|0更新时间：2020-08-11
- 摘要：Ni layer thickness and Ni layer annealing process which affect Ni/ITO-p-GaN ohmic contact were studied through CTLM,I-V curve,surface morphology,optical data etc.It was found that the Ni layer can help the formation of ohmic contact for ITO/GaN and the contact resistance reduced at first and then increased with the thickness of Ni layer.The best ohmic contact electrode was got with Ni layer thickness of 6 nm,while the contact resistance of Ni/ITO on p-GaN was 9.5×10-5 Ω·cm2 and the transmittance could reach 74% at 470 nm.This result without high temperature annealing indicated that too much thick of Ni layer is bad for the formation of NiO which could be related to low-resistance ohmic contact.How the Ni layer affect ohmic contact through annealing to Ni layer directly at oxide atmosphere was studied.The experiment showed that the contact resistances increase with annealing temperature.The NiO could be helpful to the formation for ohmic contact.But if the intermediate semiconductor layer(ISL) can't reduce the Schottky barrier height(SBH) of Ni/GaN interface much,the contact resistance will increase.It is easy for carrier injection where there is Niatom,which can promote the character of ohmic contact better.According to the experiment results,a new method named low temperature(L-T) oxided Ni layer was proposed.This method can reduce ohmic contact resistance,better surface morphology and improve reliability of LED device.关键词：p-GaN;Ni-indium tin oxide(Ni/ITO);ohmic contact220|322|0更新时间：2020-08-11
- 摘要：The junction temperature of LED has directly influence upon light output efficiency,device life time,reliability,emitting wavelength of LED.With the invention of high-power LEDs,the requirement for drive current has increased significantly,thereby increasing power dissipation.But only approximately 5% to 10% of the input electrical power in LEDs is dissipated optically while the other portion produces heat energy based on the current technology.Specially,the heat inside high-power LEDs rely mainly on natural cooling,but no active cooling was used because the active cooling will increase the cost,decrease the reliability,and shorten life time of the whole LEDlighting system.Only if the cost of each lumen(for example,USD/lm) in the semiconductor lighting is lower than other lighting source,the semiconductor lighting could replace the conventional lighting sources.So,effective thermal management of high-power LEDs must be dealt with by way of low cost and natural cooling.Keeping the junction temperature of LED in the given range is a main research goal of chip fabricating,device packaging and application.Specially,it's also a key issue being dealt with during packaging and application of high-power LED.The influences of pn junction temperature on capabilities of LEDs are described in this paper,firstly.And then the relations of junction temperature and thermal resistance of high-power LEDs are analyzed.The conclusion that junction temperature and thermal resistance restrict farther developments of high-power LEDs has been deduced based on the thermal resistance analyses of high-power LEDs.Meanwhile,the following viewpoints is put forward:(a) How to increase light output efficiency is a basic sticking point in process of raising the power of LED devices.(b)There is no point in developing high-power LEDs which go beyond 5 W for engineering applications if the light output efficiency of LEDs has no improvement.关键词：high-power LEDs;junction temperature;thermal resistance116|130|23更新时间：2020-08-11
- 摘要：Single crystal ZnO has large number of potential commercial applications,so it is important to get the centimeter-size crystals of high purity,high quality ZnO.The hydrothermal method is a good method to get high quality ZnO crystal.The different mineralizer have different influence on the crystal synthersize.The(influence) of different mineralizer on the morphology of ZnO crystal synthesized by hydrothermal method have been got.In this paper,ZnO crystal with some kinds of shapes were obtained when KOH or NaOH used as mineralizer at 350℃ with the factor of 35%.The concentration of mineralizer were changed within 2 mol·L-1to 6 mol·L-1.When the concentration of KOH was 2 mol·L-1,the product was only micron-scale crystal.With the increasing of concentration of KOH,the larger crystal began to exist,the lenghth of largest crystal reached 50100 μm.The exposed faces were usually negative polar faces {0001},negative cone faces(p{1011},)hexagonal faces m{1010}.While NaOH was used as mineralizer,when the concentration of NaOH was 2 mol·L-1,the larger crystal was present in the product and the length of the largest crystal was about 100 μm.When the concentration of NaOH increased,the length of largest crystal was longer than that with KOHas mineralizer and reached 200~300 μm.The exposed faces were integrate hexagonal faces m{1010},but the underside and cone faces of crystals were limited.So we can draw the conclusion,both the kinds and concentration of the mineralizer have obvious influence on the morphology of ZnO crystals,but under the same condition,the length of largest crystal was longer with NaOH as the mineralizer than that with KOH as the mineralizer.关键词：hydrothermal method;ZnO;mineralizer;morphology117|120|1更新时间：2020-08-11
- 摘要：ZnO a wide direct-gap semiconductor,attracts as much attention as GaN in optoelectronics research field.Recently,there has been a great progress in the growth of ZnO thin films.But applicable ZnO optoelectronic devices have not been fabricated yet,mainly due to that sufficiently effective p-type ZnO thin films have not been obtained up to now.To solve the p-type doping problems,it is necessary to grow higher quality ZnO thin films.One of the key issues to grow high quality ZnO thin films is to find a lattice matched substrate.GaN and ZnO have close lattice constant and the mismatch of them is less than 2%,so GaN is the suitable substrate for the growth of ZnO epitaxial layers.At present,the technique of growing high quality GaN films on Al2O3substrate has developed mature through the research of more than ten years,it is a feasible method to use the GaN epilayer as the buffer layers on other substrates for the growth of ZnO epitaxial layers.ZnO films used in this study were grown by a home-built vertical atmospheric pressure MOCVD system.The GaN/Al2O3 templates were fabricated by a low-pressure MOCVD system Thomas Swan,CCS.The thickness of the GaN layer was about 3 mm.We used deionized water and Zn(C2H5)2 as the O and Zn sources,respectively,and nitrogen as the carrier gas.The thickness of the ZnO layer is 2 μm.ZnO epilayer characteristics were investigated by AFM,DCXRD and PL.XRD spectra showed that the threading dislocation density of the ZnO films is in the order of 108 cm-2,which is comparable to device-level GaN films.The ZnO films showed very bright near band-edge luminescence is at 3.263 eV at room temperature and the deep-level emission is quite weak in the whole spectrum.The absence of the deep-level emission peak indicates that the ZnO films are of excellent optical quality and have few interior defects.From the low temperature PL spectrum,the domination of free exciton and the appearance of its two replicas strongly further prove the high quality of the ZnO films.This superior optical feature is an indication of the potential of atmospheric pressure MOCVD for ZnO growth on epi-GaN/Al2O3 templates.关键词：MOCVD;GaN/Al2O3;AFM;DCXRD;PL112|67|1更新时间：2020-08-11
- 摘要：ZnO is a wide band-gap semiconductor with good electrical,optical and piezoelectric properties.ZnO has a large exciton binding energy of 60 meV,which is 2.4 times that of GaN.ZnO is extensively studied because of its potential applications in various fields,such as gas sensor,solar cells,photodetectors,light emitting diodes(LEDs) and laser systems etc.Especially,after optical pumped UV lasing of ZnO films was reported,ZnO has received more and more attention from researchers.ZnO films have been grown by many different methods,such as sputtering,molecular beam epitaxy(MBE) and metal organic chemical vapor deposition (MOCVD) and so on.Among them,MOCVD provides the advantage of growing high-quality films due to its versatility in controlling the various therm odynamic interactions.In order to obtain the high-quality ZnO films,the growth technique of using the buffer layer has been adopted in the growth process of ZnO films.However,there has been few reports on the effect of ZnO buffer layer thickness on the properties of ZnO thin films.ZnO thin films have been grown on c-axis orientated sapphire substrate with MOCVD technique.Before the growth,various pretreatments for the surface of the substrate were applied and their effects on quality of the samples were observed.By measuring X-ray diffraction of samples,we observed the effects on crystal quality of ZnO thin films after surface pretreatments.At room temperature,we investigated PL spectra of the samples by excitation of He-Cd laser at 325 nm and observed the effects of pretreating on luminescence characteristic of the samples.We tested electrical characteristic of the samples by HL 5500 Hall system.By pretreating in oxygen,the resistivity of the film increased and Hall mobility declined.On the contrary,the resistivity of the film declined and Hall mobility increased by pretreating in nitrogen.The surface morphology,the structural and optical properties of ZnO films were improved by pretreating the surfaces of the substrates.关键词：ZnO thin film;MOCVD;pretreatment121|110|0更新时间：2020-08-11
- 摘要：ZnO nanostructures are very promising for applications in field emission displays and photonic devices operating in blue and UV spectral ranges due to its wide band gap(3.37 eV) and large exciton binding energy(60 meV).Therefore,fabrication and properties of ZnO nanostructures have attracted considerable attention recently.Various ZnO nanowires have been synthesized by thermal vapor transport and condensation method from the pure Zn powder or a mixture of ZnO In2O3,and graphite powder with a air pressure or a N2/O2 pressure.By varying the experimental conditions,we found more ZnO nanostructures such as tetrapods,combs,nanorods and nanobelts.These nanowires have diameters of about 50~1 000 nm,and the length range is about 1~20 μm.The structure of deposited materials was investigated by X-ray diffraction,scanning electron microscopy,transmission electron microscopy and selected area electron diffraction,which reveals the shape of all the ZnO nanowires are hexagonal structure.The luminescent properties of ZnO tetrapods was investigated by excitation spectrum and PLspectrum.The PLspectrum excited with the 210 nm of a Xe lamp at room temperature revealed a strong green emission band centered at about 500 nm with FWHM about 90 nm and a weaker near UVemission band centered at about 380 nm with FWHM about 15 nm.The PLspectrum excited with 325 nm of He-Cd laser at room temperature revealed a strong and narrow near UV emission band centered at about 383 nm with FWHM about 16 nm and a weaker broad emission band centered at about 515 nm with FWHM about 76 nm.关键词：ZnO;nanowire;luminescence;thermal vapor condensation110|106|1更新时间：2020-08-11
- 摘要：Poly(p-phenylene vinylene)(PPV) and its derivatives have been investigated in electronics and photonics because of their excellent electronic and optical properties.It has been demonstrated that nanostructured PPVs are endowed with specialties for applications in new fields,such as wave-guiding and all-optical switching.(Using) porous anodic alumina with an ordered nanopore array as a template,the luminescent polymer MEH-PPV has been embedded into the nanopores as the template was immersed in MEH-PPV solution for 48 hours,then the template was taken out and washed with THF to drive out MEH-PPV chains on the surface of the(anodic) alumina template and then nano-MEH-PPV array was formed after the solvent volatilizes.It was demonstrated by analyzing of photoluminescence(PL) spectra that the optical properties of the nano-MEH-PPV array are obviously different from that of MEH-PPV film.It is also represented experimentally that the conformation of MEH-PPV in the nanopores of the anodic alumina is chain bunch.The number of MEH-PPV chains in the bunch depends on the concentration of the polymer solution for preparing the nano-MEH-PPV array.As the anodic alumina template is immersed in MEH-PPV solution with higher concentration,more MEH-PPV chains move into the nanopores to form the bunch.Due to interchain interaction,the energy bands of the MEH-PPV bunch are widened to decrease its energy gap,and then the PL peak of the nano-MEH-PPV is red-shifted.The more the polymer chains of the bunch,the wider the energy bands of the bunch and the larger the red-shift of the PLpeak of the polymer in the nanopores.So the optical properties of the nano-MEH-PPV array can be controlled by adjusting the concentration of the polymer solution for preparing the nano-MEH-PPV array.It is demonstrated by the PLspectra of the nano-MEH-PPV array annealed at different temperatures that the(relaxation) of MEH-PPV in the nanopores is limited and the nano-MEH-PPV shows highly thermal stabilities.关键词：PPV and its derivatives;photoluminescence;nanostructured materials99|95|0更新时间：2020-08-11
- 摘要：Y2O3 has highly chemical durability,thermal stability and a relatively low phonon energy(430~550 cm-1).These aspects make Y2O3 a promising host for upconversion applications.Y1.98Yb0.01Er0.01O3 nanocrystalline powders were prepared via a co-precipitation method using nitrates,ammonia and ammonium hydrogen carbonate as raw materials.The X-ray diffraction results showed that the as-prepared powders were cubic phase of Y2O3 after fired at 700℃ for 2 h.Field emission scanning electronic microscopy revealed that most of the particles were nearly spherical and the average diameter of the particles was in the range of 60~80 nm.The upconversion spectroscopic properties of the powders were investigated under the excitation of a 980 nm continuous wave diode laser.Strong red and green upconversion emissions which centered at 660 nm and 562 nm respectively were observed.The red emission was assigned to the transitions of 4F9/2→4I15/2 energy levels of Er3+ ions,while the green emission was attributed to the transitions of 2H11/2/4S3/2→4I15/2 energy levels of Er3+ ions.The dependence of the intensity of upconversion emissions upon the excitation power of the diode laser suggested that two-photon absorption processes are involved in the green and red upconversion luminescence.The excited state absorption of Er3+ ions and the energy transfer from Yb3+ to Er3+ ions are main upconversion mechanisms.Due to its highly efficient upcovnersion luminescence,this material could find applications in the fields of fluorescent labels and infrared detection.关键词：Y2O3 nanocrystalline powders;upconversion luminescence;excited state absorption;energy transfer113|64|8更新时间：2020-08-11
- 摘要：A method to prepare crystal silicon nitride nanofibers by polysis of polymer with the assistant of FeCl2 catalyst has been presented in this paper.Scanning electronic microscopy(SEM) showed that the size of the nanofibers mostly are 100~200 nm in diameter and up to several microns in length.The growth mechanism can be explained by vapor-liquid-solid(VLS) model.The XRD pattern of the nanofibers indicated that the fiber belongs to α phase and no other crystalline phases were detected.The optical properties of the single crystalline α-Si3N4 were characterized by absorption and photoluminescence(PL).The optical absorption spectrum showed the relationship between absorption coefficient a verse photo energy hν.In order to investigate the optical band gap of α-Si3N4 nanofibers,we plot the relationship between(αhν)2 and photon energy hν.A linear relationship was observed.That the nanofibers exhibited direct-gap semiconductor behavior with band gap of ～4.80 eV,which is different from pure Si3N4(5.0~5.3 eV).This is possible because the catalyst of Fe is dopped and the Fe element affects the silicon-nitrogen molecular vibration and the states within the band gap of the silicon nitride.Intensive luminescence was observed by bare-eye.The broad emission band can be divided into two discrete broad peak by gaussian type peak fitting.The intensive optical emission are at 1.71 eV and 2.18 eV in PLspectrum at room temperature.It is believed that there exists Si dangling bonds between N3 and Si(called K center) and another point defect identified as the N dangling bonds between Si2 and N(called N center).These point defects consist of an unpaired electron largely localized on a two-coordinated N and on a three coordinated Si atom,respectively.The two defects give rise to different states,the N center corresponds to a level in the valence band,while the K center is associated to a state in the middle of the gap.The PL emission associates to the inherently imperfect Si and N dangling bonds in the α-Si3N4 structure.The PL mechanism and other related properties need to be further studied.关键词：polymer;silicon nitride;nanofiber;absorption spectrum;photoluminescence115|113|0更新时间：2020-08-11
- 摘要：The studies on the luminescence property of complexes of rare earth benzoate are attracting people's more interest increasingly.The luminescence of both complexes of Eu-Tb benzoate and complexes of Eu-La benzoate have been reported already;a high efficient Tb-Gd benzoate luminescence material was obtained by replacing a part of Tb3+ with Gd3+;also fluorescence intensity can be enhanced by replacing a proportion of Eu3+ with La3+.But interrelated report about Ca2+ and Ba2+ alkaline earth ions effecting fluorescence intensity of Eu3+ was not seen yet.So group members decided to complete this work by choosing facile alkaline earth metal and it has significant value if corking effect was gotten.Aim at this,a series of complexes of benzoic acid with europium-calcium and europium-barium were synthesized by the reaction of europium chloride and calcium chloride(or barium chloride) with sodium benzoate in aqueous solution.Their composition is expressed with the general formula(Eu1-xCax)L3-x and(Eu1-xBax)L3-x,where L=C6H5COO-,x=0~1.0).Their infrared and fluorescence spectra were investigated.The characteristic asymmetric(νas) vibrations of carboxyl group for EuL3,(Eu1-xCax)L3-x and(Eu1-xBax)L3-x(x<0.7) shift to lower frequency and the other complexes shift to higher frequency;in comparison with symmetric(νs) shift to lower frequency for EuL3 and the other complexes shift to higher frequency.What is more,both the absorption bands(νas and νs) show splitting.From above analysis,we could draw a conclusion that the coordinating pattern of the carboxyl groups in the complexes is the form of chelating-bidentate and the tridentate chelating-bridging.The dependence of the relative fluorescence intensity of the complexes upon the content for Ca2+ ion and Ba2+ ion was discussed.The results showed that the emission intensity for Eu3+ ions can be greatly enhanced if a part of Eu3+ ion in europium benzoate was substituted by Ca2+ ion or Ba2+ ion.When x=0.1,the fluorescence intensity of the complexes is the highest.So it can be saying that not only the reserves abundant and inexpensive alkaline earth metallic ions were adulterated into complexes but higher fluorescence intensity than pure europium-benzoate complexes was achieved.These research results are very successful and will have wider application foreground.关键词：complexes of Eu-Ca benzoate;complexes of Eu-Ba benzoate;benzoic acid;fluorescence spectra92|70|1更新时间：2020-08-11
- 摘要：Organic light-emitting diodes(OLEDs),which based on the electroluminescence of organic semiconductors,are promising for novel flat-panel display and lighting applications with many fascinating characteristics.OLEDs' performance is essentially and directly determined by the organic semiconductor materials and photo-physics/chemistry processes in the materials.This paper is mainly concerning the photolumine-(scence) characteristic of a typical organic small molecular fluorescent dye,DCM,in different solvent by analyzing the fluorescent spectra of the solutions with different concentration.It offers a probe for interaction between the organic material molecules,i.e."concentration quenching effect",and the surrounding solvent molecules,i.e."solvent effect" which impact on DCM photoluminescence characteristic.It was found that the peak emission wavelength(λmax) of the DCM solutions took a red-shift as the solvent's polarity increased,along with an increase in the fluorescent intensity while the λmax varied from 569 nm for the non-polar solvent,benzene,to 627 nm for the highly polar solvent,dimethylsufoxide(DMSO).It was also found that DCM solutions with a concentration of 10-6 mol/L exhibited the highest fluorescent intensities while DCM solutions with heavy concentration exhibited lower fluorescent intensity due to concentration quenching effect.关键词：organic light-emitting materials;DCM;solvent effect;concentration quenching effect115|90|0更新时间：2020-08-11
- 摘要：Cadmium zinc telluride(Cd1-yZnyTe,CZT) is the first choice of material for room temperature X-ray and gamma-ray detectors.The common growth techniques are the conventional vertical Bridgman and the high pressure Bridgman method.CZT's large average atomic number,Z～50,makes photoelectric absorption the dominant interaction below 250 keV,and its high density,5.8 g/cm3,results in short interaction lengths.CZT's large band gap also results in low leakage current and low noise at room temperature.In this research work,the improved vertical Bridgman crystal growth method is used to grow CZT crystal with a nominal Zn concentration of 15 atomic percent,namely Cd0.85Zn0.15Te.Through by strictly controlling of the cadmium vapor pressure,the high quality CZTingots were obtained.The characterization by several method of CZT(wafer) resulted in,FTIR transmittance T>60% within spectra range 2.5～20 μm at room temperature,the density of precipitate <1×104/cm2 with the precipitate diameter ≤15 μm,dislocation etch pit density DEPD<6×104/cm2,full width at half-maximum of X-ray rocking curve values FWHM<20 arcsec with the Cu Kα1 radiation and Si three-crystal monochromator and 15 mm×15 mm spot size,the electrical resistivity ρ>1010 Ω·cm.The single element planar detector for radiative ray detection fabricated with CZT crystal mentioned above is performed.The size of CZT crystal for detector is 5 mm×5 mm×2.5 mm.On both sides of 5 mm×5 mm surface,gold and gold/platinum were evaporated as electrodes.The energy spectra to standard radiation source 125I and 241Am were performed by CZT planar detector.The applied bias voltage for CZTplanar detector is 200 V.The characteristic γ-radiation peak of 125I at 27.5 keV with intensity 74.5% is detected and the characteristic γ-radiation peak of 125I at 27.2 keV with intensity 39.8% can not be recognized from the energy spectrum for 125I.The characteristic γ-radiation peak of 241Am at 59.5 keVis measured with the full width at half-maximum FWHM<10%,viz.the resolution is better than6 keV.In the mean time,the characteristic X-ray escape mixing peaks of tellurium and cadmium located at 34 keV is detected and two characteristic X-radiation peaks of Te-Kα1,α2 at 27 keV and Np-Lβ1 at 17.5 keV are also recognized.关键词：ray detector;cadmium zinc telluride crystal;Bridgman growth method;X-ray;gammaray110|86|6更新时间：2020-08-11
- 摘要：Lixiscope is made up of X-ray source,X-ray image intensifier and high voltage power supply.(Among) them the X-ray cathode is the key in technology of image tube.Soft X-ray usually means that waveband is between in 0.012 nm and 0.062 nm(tube voltage at 20~100 kV).Corresponding X-ray cathode have two types:transmission and reflection type,which is used to realize the conversion function that X-ray transferred to photoelectrons.And at present X-ray cathode in X-ray image intensifier that applied in our country with Microchannel plates(MCP) is mostly CsI/MCP structure.One of them is with dense structure or dense-loose-dense structure(loose layer is very thin),but the end surface of MCP is pervious,it works in the form of reflection type.Another one is dense-loose-dense structure(loose layer is very thick),but most of the end surface channel of MCP is stop up,it relies mainly on transmission type working way and complementally on reflecting type working way.Exploring its making technology,studying its quantum detection efficiency analyzing its noise characteristic,improving the characteristic of image tube and system are the top priority tasks,especially there are practical meanings today that Lixiscope(Lixiscope-Low Intensity X-ray Imaging Scope) is developed fast and its use is widened even more in biomedicine.In this paper,the operation principle picture,the outputs characteristic curve and corresponding technical data of X-ray cathode is provided.The front and sectional stereo-scan photographs of CsI/MCP reflecting type X-ray cathode is provided,and available information has been offered.关键词：soft X-ray cathode;CsI/MCP structure;X-ray image intensifier;low intensity X-ray imaging scope103|79|1更新时间：2020-08-11
- 摘要：There are many studies and application about long-lasting phosphorescence powder,but not so much about long-lasting glass.Due to particular properties of glass such as being easy to be made into product with various shape in the range from thin plate to bulk plank and special optical properties.Therefore we think that the studies on long-lasting luminescence of glass are important academically.This article introduces a new way to produce long-lasting luminescence glass:Eu,Dy co-doped aluminum-borosilicate glass with a composition of 18.5%SiO2,30% B2O3,20%Al2O3,20%SrO,0.5%Eu2O3,1%Dy2O3(mol fraction).The glass are melted under air atmosphere at 1300℃ then deoxidized under CO atmosphere at 1200℃.Spectrum analysis showed that the sample without the procedure of deoxidization has no afterglow and the sample reheated under CO atmosphere has afterglow.The excitation spectrum of the sample showed a peak at about 462 nm which is due to the d-f transition of divalent europium.There is also a peak at about 578 nm that is the characteristic peak of trivalent europium.Thus the long-lasting luminescence glass is due to the characteristic emission of Eu2+ ion.In order to get higher performance long-lasting luminescence glass,we must convert more Eu3+ into Eu2+ as it could be by introducing reducer agent directly in glass or improving producing mechanics of glass.The decay of the luminescence is complex processes that consist of three parts:a fast decay;a intermi-(date) and a long decay.So the decay of the sample is compatible with the long-lasting phosphorescent powder.However the luminescence intensity of glass are far less than that of long-lasting phosphorescent powder.We considered that the formation of SrAl2O4Eu2+,Dy3+ micro-crystal is difficult in glass.So further study should be carried on the mechanism of Eu2+,Dy3+ co-doped glass and its phosphorescent properties.关键词：long-lasting luminescence;luminescent glass;Eu2+;Dy3+ co-doped99|96|1更新时间：2020-08-11
- 摘要：Azinc complex with a novel schiff base,ZnL,was synthesized and characterized by elemental analyses FT-IR,UV-vis absorption,fluorescence spectra,DTA-TG and cyclic voltammetry,in which the ligand compound is N,N'-bis(2-hydroxy-1-naphthylidene)-3,6-dioxa-1,8-diaminooctane(H2L).The blue fluorescence with peak at 455 nm of the complex either in solution or in solid films was observed under excitation by 385 nm.The electroluminescent(EL) devices with the ZnL complex as the emitting layer were fabricated and they exhibit bright blue ELemission and the maximum brightness is 650 cd·m-2,the external quantum efficiency is about 0.63 cd/A at a bias voltage of 9.5 V.关键词：open-chain crown;Schiff base zinc complex;fluorescence spectroscopy;organic electroluminescence102|99|0更新时间：2020-08-11
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