最新刊期
卷 22 ， 期 2 ， 2001
- 摘要：The Ag-BaO are composite thin films in which metallic nanoparticles are embedded in semiconductor matrixes.It has an ultrafast response time of photoemission and can be used for detecting ultrashort duration laser pulses.After applying a vertical electric field on the surface of thin films,the efficiency of photoemission can be increased.The Ag-BaO thin films were prepared by vacuum evaporation.The total thickness of thin film was 200～300nm,but the thickness of the Ag-BaO thin films was 100～140nm which got rid of the thickness of the above and bottom electrodes.The thin films presented obvious enhanced photoabsorption in the near ultraviolet region when a vertical electric field was applied to the surface of the thin films.The photoabsorption at wavelength λ=303nm was increased by 6.5% and 18% stimulated by vertical voltage 15V and 30V on the surface,respectively.The reason of enhanced photoabsorption is that the energy band of thin film becomes oblique and split under the application of a strong electric field.Through absorbing the energy of photons,excited electrons trend to increase the probability for tunneling in oblique energy band and for transition between split energy levels.关键词：thin film;vertical electric field;photoabsorption93|82|0更新时间：2020-08-11
- 摘要：The motion characteristics of the magnetic thin film have been studied under various forms of applied magnetic field(AMF):pulse,A.C. field and D.C.field [1～6].In present paper,the dynamic behaviour of the magntooptic thin film under the composite fields has been measured experimentally.The formula of magnetooptic specimen is BiTm)3(FeGa)5O12,which has two surface with thickness of 6 19×2μm.The AMF corresponding the saturation Faraday's rotation angle is 8000A/m.The domain wall(DW) can be considered as the 180 degree wall and the equivalent resistant field is the order of 1000A/m in the thin film specimen.There are three forms of AMF:type A,low frequency A.C.(the amplitude 140A/m) produced by a function generator;type B,uniform magnetic field sweeping(UMFS,d H/dt=83.6A/m/S in present paper,H is the magnetic field) produced by a D.C. power supply with a sweeping rate control system [6];type C,the UMFS together with low frequency A.C.field.We remark the type C as the composite field.The data of DWs motion have been obtained by means of the computer with charge couple device(CCD) and of photography from the polarization microscope.The transformer put on the stage of the microscope was prepared a fair hole to lay up the thin film specimen and was connected to the D.C.power supply or/and to the function generator for carrying out AMF.The average distance of DWs from the photography for various experiment conditions of H could be plotted against the time.The percentage data of DWs area from the CCD for various experiment conditions of H do the time in the same grapher.After comparing the dynamic character of DWs with these curves corresponding to 0.1～10Hz A.C.fields or/and to H/dt=83.6A/m/S UMFS rate,it can be shown that: (1)The motion behaviors of DWs in the AMF of type C are not the same as that of simple composition of type A and type B,it would be an interaction term represented the force between AMF and DWs [7].(2)Even if the amplitude of A.C.field value 140A/m1000A/m,the equivalent resistant field [6],and the value of D.C.field100A/m,the DWs of the thin film specimen can be moved.The motion of DWs is not synchronized with the AMF.It is supposed that the DWs may be easier to move and can be pushed forward or pulled back by a small D.C.field superposed a weak A.C.field.关键词：magnetic thin film;domain wall motion;interaction88|47|0更新时间：2020-08-11
- 摘要：Micro Raman scattering was employed at room temperature to investigate the properties of GaInP2 alloys grown by MOVPE.The excitation wavelength is 5145nm.The geometry is back-scattering.GaInP2 has CuPt-like ordered structure along [111] which results in special optical properties such as the reduction of band gap,the doubling of PL peak,the temperature and excitation intensity dependence of photoluminescence,the splitting of valence-band,etc.The Raman spectra show two-mode behavior.In addition to the GaP-like LO1 mode(ordered samples at 383cm-1,disordered sample at 381cm-1) and the InP-like LO2 mode around 360cm-1,the InP-like TO2 mode around 330cm-1 and the GaP like TO1 mode hidden in LO2 are observed.To alloy with zinc-blende structure,the TO mode is forbidden with back-scattering geometry under Raman selection rule.But to the CuPt like ordered structure,the TO mode becomes Raman active by the reason of symmetry reduction from Td to C3v.At the Raman shift about 200cm-1,all the samples have the same disorder-activated longitudinal acoustic bands(DALA).Besides the DALA,the ordered samples exhibit folded longitudinal acoustic mode (FLA) around 205cm-1.This mode belongs to the L point folded to the Γ point as a result of the doubling of the unit cell of Brillouin zone.The intensity of the FLA peak is believed to be stronger with increasing the degree of order.In addition to the LO1+LO2 mode,the splitting of LO2 into LO2 and LO2 in ordered samples induced by superlattice effect resulting from the atom ordering is detected.In the ordered Raman spectra,from which the disordered's is subtracted, one can tell the FLA peak and the LO2 more clearly.In addition,there is another peak around 375cm-1 which is probably the LO1 splitting from LO1.By analyzing the PL peak energy and the b/a ratio of the valley between GaP like and InP-like LO to the height of InP-like LO2,it exhibits that the value of b/a ratio reduces with the increase of ordering.On one hand,it is because that the forbidden TO becomes Raman active.On the other hand,it is probably due to the consequence of the splitting of LO1 into LO1 and LO1 and LO2 into LO2 and LO2.Besides the value of b/a ratio which represents the degree of order:the smaller the value of b/a,the greater the ordering degree,the high intensity of FLA mode also corresponds to high degree of order.关键词：semiconductor;Raman scattering;atom-ordering87|57|1更新时间：2020-08-11
- 摘要：The temperature dependence of GdVO4:Eu3+ luminescence from Eu3+ 5D0 →7FJ transition excited by 313 and 365nm of high pressure mercury lamp above room temperature has been studied including the emission spectra at different temperature and the emission intensity of Eu3+ as function of temperature.In addition,the excitation spectrum of GdVO4:Eu3+ with emission wavelength 619nm at RT was measured. The characteristic emissions of Eu3+ were observed,including 608,616,619nm of 5D0 →7F2 transition,594,598nm of 5D0 →7F1 transition and 538nm of 5D1 →7F1 transition.Each of them increases with rising temperature.And the relative intensity of the emission lines maintains constant each other.In the range of 300～600K,each emission line increases as temperature rises, especially above 400K,and there is a rapid increase without intensity saturation up to 600K.The emission intensity at 600K is twenties time stronger than that at 300K.We observed that the excitation spectrum of 619nm emission contains two main excitation bands peaked at about 250 and 310nm,beside the intrinsic excitation of Eu3+.But the intensity of intrinsic excitation is weaker than that of the excitation bands at 250,310nm. When Eu3+ is excited by 365nm which is Eu3+ intrinsic excitation,there are two ways to deplete its energy.One is cascade down to 5DJ states according to the order of 5D3, 5D2, 5D1, 5D0.The other is to be promoted thermally to charge transfer state and sequentially to feed 5D0 without passing by cascade from higher 5D state by which 5D0 can be excited more effectively.The possibility of the latter process depends on temperature intensively.Therefore,when temperature rises,more Eu3+ can be excited into 5D0.Using this model the experimental result can be explained reasonably.If Eu3+ is excited by 313nm which can be the sorption by VO43-,it can also be promoted thermally into charge transfer state. In conclusion,the intensity of the luminescence excited by 313,365nm increases rapidly as temperature rises up to 600K.The CTS of Eu3+ as a middle state plays an important role which can make the excitation energy transfer to 5D0 effectively.Such process is more remarkable when the temperature rises.With high temperature property,GdVO4:Eu can be used in high temperature environment.关键词：rare earth;GdVO4：Eu3+;luminescence;temperature properties81|58|0更新时间：2020-08-11
- 摘要：Anodically oxidized porous alumina whose structure can be described as a closepacked array of columnar cells,each containing fine,regular, almost cylindrical,parallel-sided pores,can be utilized as transparent host template for a variety of luminescent media.RhB laser dyes were successfully embedded in the porous alumina.We studied the photoluminescence of the compound films and compared it with the PL of the liquid dyes.It was found that the PL of the embedded dyes is like the PL of the liquid dyes at low concentration,but the spectra symmetry of the embedded dyes is better than that of the liquid dyes.The experimental results suggest that the laser dyes mainly exist in porous alumina in form of the monomer. To clarify the detailed state of the dyes existing in the porous alumina,we have done a series of experiments.(1)Porous alumina were formed at various anodizing time in the range 30 to 90min at constant voltage 15V in 15% sulfuric acid at 25℃.The intensity of the PL of the embedded dyes increases and the peak exhibits red shift as the anodizing time grows.(2)Porous alumina were formed at various constant voltages in the range 5V to 17V for 1h in 15% sulfuric acid at 25℃.The intensity of the PL of the embedded dyes increases and the peak exhibits red shift as the anodizing voltage increases.(3)Porous alumina were formed at 15V for 1h in sulfuric acid at 25℃,and immersed in the dyes at various concentration in the solution.RhB output from the embedded layer is as a function of dye concentration in the solution.The peak of the luminescence exhibits red shift,but severe concentration quenching is apparent for impregnation from solutions stronger than 10-2 M/L. Finally,we put forward an idealized model to explain the state of RhB laser dyes embedded in porous alumina.The dye is roughly absorbed on the wall of the pore and mainly exists in the form of monomer.关键词：porous alumina;anodization;embedded laser dyes film93|92|0更新时间：2020-08-11
- 摘要：ZnO films were deposited on Si substrates by MOCVD.Two sets of MO sources were used here.One was Zn(C2H5)2(DEZ) and CO2,another was Zn(CH3)2(DMZ) and H2O.The carrier gas was nitrogen instead of hydrogen,in order to avoid ZnO decomposed in hydrogen at high temperature.During growth process,the pressure in reactor chamber was 6000Pa and atmosphere,respectively.The growth temperature employed in the experiments were 500,550,600,650 and 700℃.Growth time was 1 hour for all samples.After growth,every sample was cut to two parts.One of them was annealed in air at 900℃ for 1 hour.The structures and photoluminescence properties at room temperature of the as deposited and annealed samples were investigated.It was found that the structure and photoluminescence properties of the ZnO films markedly depends on the MO source,growth pressure and temperature.Only low growth pressure is useful for deposition of ZnO films.As using Zn(C2H5)2 and CO2,the films deposited at 500℃ are all c axis oriented.When the growth temperature increases,the ZnO(002)diffraction peak of the samples became low and low and other ZnO diffraction peaks increase.That means the orientation of crystal grains in the films tends bad,and the film becomes polycrystal.When the growth temperature was at 650℃,not only ZnO but also ZnO2 peaks appeared in XRD patterns.These properties exhibit more remarkable after samples were annealed.As the growth temperature was at 700℃,ZnO films can't be deposited on Si substrates. The AT PL spectrum of the sample deposited at 500℃ includes two emission peaks,their wavelength are 380nm and 520nm,respectively.After annealing,only one stronger 380nm peak is observed.But the appearance of ZnO2 in the samples grown at 650℃ changes the photoluminescence spectra.For the as prepared films,the PL spectrum has one peak,the wavelength is 374nm,and a new emission peak with 575nm appears after annealing. Using Zn(C2H5)2 and H2O,the deposited ZnO films are composed by high-pressure phase of ZnO.The PL spectrum of the sample grown at 550℃ exhibits green emission whose wavelength is 520nm.The emission peak of the sample grown at 450℃ shifts to 345nm.Its energy,about 3.6eV,is larger than the band gap of ZnO.The forming and effects of high pressure phase of ZnO needs to be researched in detail.关键词：zinc oxide films;MOCVD growth;structure;photoluminescence119|72|11更新时间：2020-08-11
- 摘要：Organic light-emitting diodes(OLED) have been investigated for over 10 years and have been in a stage ready for commercialized applications.However,the stability or the lifetime of OLED is still a major issue to be further investigated.As is known,the stability of OLED is closely related to processing techniques,and the quality of each processing steps could be evaluated by some test methods.Here,we proposed a simple method for the fabrication test of OLED—"Observation of covered and heated films",which is completely compatible with the technique of OLED fabrication. In this method,a hole transport layer (such as N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-(1,1'-biphenyl)-4'4-diamine(TPD)) is firstly deposited on a half of indium tin oxide(ITO) surface,and then the mask used for patterning was turned into 90° to let the following deposited electron transport layer (such as tris (8-hydroxyquinoline) aluminum(Alq)) be perpendicular to TPD layer.After the deposition of organic films,a layer of low air permeable film(such as Al film) was deposited on the substrate as a covering film.Therefore,four different areas were formed on the same ITO substrate with the layer structurs of Al/Alq/TPD/ITO,Al/TPD/ITO,Al/Alq/ITO,and Al/ITO,respectively.The as-prepared sample was then treated by rapid heating.Lastly,the thermal treated sample was used for microscopic observation. By using this method,gas bubble formation and organic crystallization on the sample surface were observed.The effect of annealing temperature,ITO surface treatment,and purification of organic sources on the bubble formation were also observed.As increasing the annealing temperature,the induced bubbles from organic layers were getting bigger in size(larger than 50μm) and more in numbers,while the bubbles induced from ITO surface were limited in a size less than about 10μm.No bubbles can be observed if ITO surface was thermally treated before any deposition of organic films.And bubbles can be reduced if organic sources were purified by sublimation before use.It is indicated by the experiment that the method of "observation of covered and heated films" is a useful method to evaluate the quality of fabrication,and therefore to improve the performance of OLED.关键词：organic films;thermal treatment;morphology;fabrication evaluation122|80|0更新时间：2020-08-11
- 摘要：There exists a considerable amount of work,both theoretical and experimental,on the system of electrons on the surface of liquid helium.Because of the combined effect of the attractive image potential and the surface barrier,electrons are confined to move on the outside surface of the liquid and form an ideal two dimensional(2D) system.In recent years the ripplon problem has been studied by many theoretical methods and the properties of the ripplon are measured using experimental method by many investigators. A polaron is a system of an electron on the surface of liquid He film coupled to the ripplon field,an elementary excitation of the liquid helium surface.The system is of particular interest,because the strength of the electron-ripplon coupling can be changed by adjusting the thickness of the film and by changing the substrate material.However,because the forms of the ripplon dispersion relation and the electron ripplon coupling are more complex,hence the polaron problem of an electron-phonon coupling in crystals is different from an electron ripplon coupling on the liquid helium surface.The theory was established by Jackson and Platzman.They studied the ground state of the system by means of Feynman formulation of polarons,and found the ground-state energy,in both the weak-and strong coupling limits.Stan et al. studied the variation of the electron effective mass and the rate of ripplon scattering from the electron arrays as a function of temperature.Jin et al.investigated the properties of strong coupling system of the electron ripplon on liquid helium film by Landau-Pekar variational theory.In fact,so far research of the effective mass of an electron ripplon coupling system on the surface of liquid helium film is very scarce.The purpose of this paper is to explore the effect of the electron interaction with both the weak-and strong coupling ripplons on the effective mass of 2-D electron coupled to the ripplons on the surface of liquid helium film by using a linear combination operator and Lagrange multiplier method. The results show that for the weak coupling the additional part of the effective mass of the polaron is proportional to the coupling constant α and for the strong coupling the vibration frequency λ of polaron depends not only on the cutoff frequency Kc,but also on the coupling constant α,thereas the frequency λ will increase with increasing Kc and α.The effective mass of the polaron M* will increase with increasing electron ripplon coupling constant α,thereas the self energy of the polaron will decrease with increasing coupling constant α.关键词：liquid helium;ripplon;2D-electron;effective mass96|117|0更新时间：2020-08-11
- 摘要：In recent years,the subject of optical nonlinearity in semiconductor quantum confined structures such as quantum wires and quantum dots has attracted a considerable attention because of their relevance for studying practical applications and as a probe for the electronic structure of media.It has been shown that the low-dimensional quantum systems present very large nonlinear optical susceptibilities.Theoretically,most of the studies on quantum dots are focused on spherical quantum dots for simplicity.The shape of quantum dot depends on growth conditions.In fact,quantum dots are better described as thin disk or cylinder.In the present work third-order nonlinear optical susceptibilities in disk-shaped quantum dots due to resonant intersubband transition are analyzed by a compact density matrix approach.It has rarely been discussed in literatures.Firstly,we consider an electron moving in a quantum disk whose radius R is very large compared to its thickness d.For simplicity,we assume that the isotropic effective mass approximation is valid within the disk and that the inner potential is null while the outer confining potential is approximately infinite.Using the adiabatic approximation we solve the three dimensional Schr-dinger equation and obtain the analytical expressions of wave functions and energy levels in cylindrical coordinates.Secondly,we consider the system is excited by an electromagnetic field with frequency ω. The electromagnetic field is incident with a polarization vector normal to the disk.We treat H'=ezE(t) as a perturbation term.By using the compact density matrix method,we derive a general formula for third order nonlinear optical susceptibilites employing a four-level model in quantum disk.Finally,numerical results are illustrated for a typical GaAs quantum disk.We calculate the third-order nonlinear optical susceptibilities as a function of the disk thickness.It is shown that the third order nonlinear optical susceptibilities in quantum disk are 10～100 times larger than that in quantum well for various disk thickness.Furthermore,if we choose an optimized thickness of quantum disk,we could obtain a quite large refractive index with a comparatively small absorption coefficient.Therefore,we suggest that the quantum dots would be an excellent system in the field of optical communications and optical switching.关键词：third-order nonlinear optical susceptibility;quantum disk;density matrix operator95|96|1更新时间：2020-08-11
- 摘要：The trivalent rare earth ions have partially filled 4fN shell.In the free atomic states,4fN electrons contributes to same parity.In the bounded state,static crystal field leads to the mixing of opposite parity configuration,accordingly electronic dipole transition between 4fN configuration is allowed.Judd-Ofelt obtained the relationship between crystal field and the transition intensity based on the configuration mixing theory,and built up a method for calculating the transition intensity parameters from the absorption spectra.But the use of J-O theory is limited,because in a lot of conditions the measurement of absorption spectra is difficult. In this work,the absorption,excitation and emission spectra of Eu3+ doped glasses,which contained PbF2 and H3BO3,was measured.The refractive index of different glasses was calculated.The Ω2 and Ω4 parameters of Eu3+ for optical transition were calculated,in terms of reduced matrix U(t)(λ=2,4,6) character for optical transitions.The dependence of the Ω2 and the Ω4 parameter on the content of H3BO3 was obtained and discussed.The purpose of this work is that,using the Eu3+ as a probe to study the microenvironment in glasses.Lastly we attest to the possibility of this purpose in experiment.关键词：rare earth;optical transition;J-O theory105|95|14更新时间：2020-08-11
- 摘要：A method of analyzing the laser stability based on the linearized equation is presented.The operating state of a laser can usually be described through the rate equations of photons and population inversion, these equations are a set of nonlinear equations.Therefore,laser is indeed nonlinear device.The stady state solution of the rate equations gives the threshold condition.The steady-state solution is merely an equilibrated point of the nonlinear equations,the laser could not work in the case of steady-state.Steady state solution being stable or unstable is so-called the stability problem of laser. Based on the Poincar? nonlinear theory,to study the stability of the steady point of a system,the time evolution of the system experienced perturbation near the steady point must be examined.The method of the analysis is that the rate equations are firstly expanded as a Taylor series and the nonlinear terms are ignored,then the linear equations are obtained.This linear system has the same properties as the nonlinear system under small perturbation.Therefore,the linear equations can be used instead of the nonlinear equations for analyzing the system stability. The type of the steady-state of the linear equations can be determined by the invariant of the coefficients matrix,i.e.,the trace,determinant and discriminant of the matrix.Particularly,the knowledge can be obtained that the type of the stability could be changed above the threshold.Furthermore,if the time variation of the process parameters are taken into accout,the knowledge can also be obtained that the laser chaos can certainly occur.关键词：laser;stability113|98|0更新时间：2020-08-11
- 摘要：Organic nonlinear optical materials have stimulated much interest for their large nonresonant nonlinearities, high-speed response, ease of fabrication and low cost. There are a number of different ways to fabricate polymer channel waveguides, such as reactive ion etching and groove filling etc. This paper reports a simple technique of UV photobleaching which can be used to prepare ridge channel waveguide with DANS (4-dimethylamino-4'nitro-stlibene)-PMMA (polymethyl methacrylate) side-chain polymer film. UV photobleaching is an attractive method for fabricating polymer optical waveguides because the process is simple and exposure time can be adjusted easily, so as to control the refractive index changes of the polymer film. The corresponding main technique is discussed in the paper. The complicated photochemical reaction will happen when DANS-PMMA side-chain polymer film is exposed to the high pressure Hg lamp. We can notice that both the refractive index and the thickness of the DANS-PMMA film are reduced after photobleaching. This process is usually called UV photobleaching of the polymer film. For DANS-PMMA film, we have processed a series of UV photobleaching experiments. Under appropriate UV photobleaching condition, combined with metal covered technique, a new type of DANS-PMMA polymer ridge waveguide was prepared. First, the Al film was deposited on the surface of DANS-PMMA film and formed pattern of waveguide by photolithography and etching. Second, the sample was exposed to the high pressure Hg lamp for some time. Then, the new type of ridge waveguide is formed. Besides, the technique does not require photolithography or etching on polymer film, so very flat waveguide side walls can be formed. With the microscope we can observe the perfect shape of the DANS-PMMA ridge waveguide.The smooth walls of the ridge waveguide are helpful to reducing the scattering losses and improving the quality of the waveguide. The experiment proved that UV photobleaching process depended on time, distance and temperature of bleaching. The rate of UV photobleaching will increase when environment temperature is risen.关键词：UV photobleaching;side chain polymer DANS-PMMA;ridge channel waveguide109|105|0更新时间：2020-08-11
- 摘要：GaInNAs alloy has recently attracted considerable attention for both fundamental physical properties and its possible optoelectronic application in long wavelength optoelectronic devices based on GaAs.In general,the interband luminescence efficiency would be decreased when N atoms are incorporated to form GaNAs and GaInNAs alloys,partly due to a large miscibility gap and phase separation of GaN and GaAs,or the formation of N clusters.It is well known that the incorporation of both In and N will reduce the energy gap of the alloy.Their band shrinkage effect is additive.Therefore,in order to obtain the high quality alloy material and to improve the interband luminescence efficiency in the 1 3 and 1 55μm wavelength region,the study of optimal condition for incorporating N and In atoms into GaInAs/GaAs quantum wells becomes important.In this paper,both GaInNAs/GaAs and reference GaInAs/GaAs quantum wells investigated here were grown on the same (001) GaAs substrate by plasma assisted molecular beam epitaxy.The optical properties of interband transitions and below the band-edge have been investigated by incorporating In atoms into GaNAs/GaAs single quantum well.The experimental results show that with increasing In concentration the interband luminescence is improved and the photoluminescence intensity below the band edge in GaInNAs/GaAs single quantum well decreases significantly.An interpretation is given that N atoms are more preferable to form covalent bond with In than with Ga atoms in GaInNAs alloy due to the compensation of the atomic size difference between In and N atoms on GaAs substrate.Thus the lattice-mismatched GaInNAs with more In atoms and less N atoms is perhaps a better choice than the lattice-matched GaInNAs for luminescence devices.The photoreflectance spectra of the GaInNAs/GaAs single quantum well support to the assignment of the intrinsic mechanism of the high-energy luminescence peak.关键词：GaInNAs/GaAs single quantum well;photoluminescence below the band-edge;intrinsic photoluminescence98|88|0更新时间：2020-08-11
- 摘要：Recently,ZnO film has attracted much interest because of its huge potential commercial application in ultraviolet (UV) laser since its optically pumped UV lasing was found at room temperature,and the photoluminescence (PL) properties of ZnO films have been studied widely.Some early works indicate that the peak excitation of the UV band should be in the vacuum ultraviolet (VUV) region and the intensity of Xe lamp is not enough to excite them.In the present work,a detailed study on the PL properties of ZnO film deposited on Si substrates by reactive DC sputtering was carried out with a synchrotron radiation (SR) light source for the first time to our knowledge. The excitation and emission spectra were measured at HASYLAB,DESY at Hamburg,Germany.The excitation spectra show a strong excitation band around 195nm related to 390nm emission band.Under SR vacuum ultraviolet excitation,a new emission band peaked at 290nm was found for the first time,besides the ultraviolet emission band (390nm) and green band (520nm). Since the energy of 290nm emission photon is larger than the band gap energy of ZnO (3.2eV),it does not originate from the band gap radiative recombination or intrinsic defects, as well as impurities.The excitation spectra of the two emission bands are very similar to each other,which also prove that the 290nm emission originates from ZnO film itself.In addition,it seems also not come from the Si substrate,because the VUV light is strongly absorbed by ZnO film (0.2μm) and can not reach the substrate. In conclusion,the newly found emission band peaked at 290nm indicates that there are some structures in the conduct band of ZnO film.The excitation spectra show that the strong excitation bands are in VUV region (photon energy higher than 6eV),but almost no excitation in the lower energy region.The strange behaviors in the PL properties of ZnO film may be one of the reasons that few report is found in the past,and also imply that more detailed experimental as well as theoretical studies should be carried out in the future.关键词：ZnO film;photoluminescence;synchrotron radiation92|91|4更新时间：2020-08-11
- 摘要：In resent years there has been great interest in combining ferroelectric thin films with semiconductor materials.If integration between ferroelectric materials and semiconductor materials can be achieved directly in epitaxial growth,it would open possibilities to explore new applications and new physical phenomena. This paper reports the molecular beam epitaxy(MBE)growth of the GaAs films on the SrTiO3 substrates with different orientations ((100),(110) and (111)).Micro-Raman and photoluminescence(PL) measurements are used to detect the optical properties of these new kinds of heterojunction structures.Two Raman peaks near to 269 and 292cm-1 have been observed which corresponding to the TO and LO phonons of the GaAs single crystal.These show that the GaAs films are well crystallized.Micro Raman studies also show that the rate of the intensity of LO and TO peaks of the GaAs films are different for the different orientations of SrTiO3.It indicates that the orientations of the GaAs films are different. PL studies show the intensity of the PL peak of GaAs on (100) and (111) SrTiO3 are quite weak,and large blue shifts (more than 10meV) are observed.These are caused by the large difference of surface lattice periodicity and crystal structure between GaAs and SrTiO3.The intensity and the position of the PL peak of GaAs film on (110) SrTiO3 are similar to that of single crystal film.These results show the optical quality of the GaAs film on (110) SrTiO3 is much better and can compared with that of single crystal film.关键词：GaAs films;SrTiO3;photoluminescence;Raman spectra92|74|0更新时间：2020-08-11
- 摘要：The BaF X(X= Cl,Br,I):Eu2+ is a kind of photo stimulated luminescence (PSL) material.The electron and hole traps play an important role in the mechanism of PSL.Both electron and hole leave respectively their traps by photo stimulation,then recombine with light emission at the luminescence center.In BaF X :Eu2+,the vacancy of anion will attract an electron and form the F colour center which could be electron trap.Nevertheless,what will be the hole trap? It is not clear up to now.In this paper,the emission and absorption spectra of BaFBr and BaFBr:O2- samples have been investigated in order to ascertain the origin of hole traps in BaF X :Eu2+.In BaFBr:O2- sample,in which the concentration of O2- is about 8×10-3 at%,the O2- ions occupy the site of fluorine ion.At room temperature,without pre irradiation,there are some emission peaks (at 330,345 and 540nm,respectively) and shoulders (near 440,480 and 502nm,respectively) in the emission spectra of BaFBr:O2-,under the excitation of 240nm,as shown in Fig.1.But,no luminescence can be observed for BaFBr.However,for both BaFBr and BaFBr:O2-,similar luminescence can be seen,after the pre irradiation with ultraviolet and vacuum ultraviolet(VUV) light of 50～400nm and/or 185nm,under the exitation of 240nm.Their emission peaks locate at 332,348,390,442,467,502 and 540nm approximately, although,the relative intensities of these peaks have minor differences for both samples(Fig.2).We believe that the origin of the luminescence of BaFBr and BaFBr:O2- is due to the oxygen impurity. Furthermore,taking the reflection spectrum of Au thin film as reference,the reflection spectra of BaFBr and BaFBr:O2- samples are measured in the range of 100～400nm at U10B station of the National Synchrotron Radiation Laboratory(NSRL).The absorption spectra are calculated from these reflection spectra by using K-K relation.It is found that there are four broad absorption sub bands in the absorption spectra of BaFBr,as well as in that of BaFBr:O2- (Fig.4).It means that the electron can be excited or ionized from the oxygen impurity into F center by UV and VUV light.These results support that the oxygen impurity could act as the hole trap in PSL materials.关键词：photo-stimulated luminescence;hole trap;oxygen;BaFBr86|66|0更新时间：2020-08-11
- 摘要：ZnO films were deposited on Si substrates by using DC sputtering and their cathodeluminescence(CL) and photoluminescence(PL) properties at room temperature were investigated. The CL spectra of the ZnO films include three peaks.They are purple(center wavelength about 390nm),blue(430～450nm),and green(522～525nm) emissions.These spectra are dependent on the crystal quality of ZnO films.The purple peak appears only in the sample whose crystal quality is good.We also observed that the intensities of purple,blue and green emissions vary with CL electron beam current density.With the increase of electron beam current density,the intensity of blue peak increases almost linearly and the intensity of purple peak increases super-linearly.According to these phenomena,it is deduced that the green emission results from the electron transition between a donor level caused by oxygen vacancies and an acceptor level caused by zinc vacancies.The blue emission includes two transitions of electrons : from the donor to the valence band and from the conduction band to the acceptor.The ultraviolet band would be the excition transition from the band edge emission.At the same time,the wavelength of purple peak exhibits red shift with increasing the CL electron beam current density.We suggest that the increasing carrier density generated by increasing exciting power cause the luminescence center to tend to gap tail levels. Except green,blue and purple peaks,a new ultraviolet peak (334nm) appears in the PL spectra of the ZnO films.The photon energy (3 72eV) of the ultraviolet peak is much larger than the band gap of ZnO.The reason needs to be investigated in further experiments.关键词：zinc oxide films;CL spectra;PL spectra;luminescent properties99|92|6更新时间：2020-08-11
- 摘要：Three different kinds of crystal structures,face centered cubic(fcc),body centered cubic(bcc),and hexagonal close packed(hcp) structures with eight valence electrons in each primitive unit cell were studied.In thEFramework of free electron approximation,their Fermi level EF were determined by Fermi sphere according to the theory of free electron gas,and the average-bond-energies Em were calculated by free electronic band model.The calculated results of EF and Em indicate that the average bond energies Em of three different crystal structures (therefore their electron densities are different) correspond to their Fermi levels EF respectively.In the semiconductor energy band,the average bond energy Em is defined as thEmid point of the energy gap between Eb (bonding orbital energy) which is the avergage valence band level of thEFour highest valence band levels,and Ea (anti bonding orbital energy) which is the average conduction band level of thEFive lowest conduction band levels in the whole Brillouin zone eigenvalues.It is the reference energy level in our theoretical calculation of heterojunction band offset.Therefore,the relationship between EF and Em found here is helpful to understand the physical concept of average-bond-energy Em and the reason why it aligns at the two sides of the heterojunction interface.It also suggests a new method to calculate thEFermi level EF of free electron systems through free electronic band model.关键词：Fermi level;average-bond-energy;free electronic band model110|122|0更新时间：2020-08-11
- 摘要：Up to date,in seeking for the new materials for ～2μm laser,the Tm doped or Tm,Ho co-doped YAG,YLF crystals have attracted much more attention.In this paper,the measured results of spectroscopic properties in Tm,Ho co-doped YVO4 crystal were reported.The absorption spectra,fluorescence spectra and calculated spectroscopic parameters were given,the processes of sensitized luminescence of Ho3+ by Tm3+ with LD pump at 805nm were investigated.It was found that Tm3+ ion in YVO4 has a larger uniform absorption width(～26nm) and a larger peak and integrated cross section of absorption at ～800nm(～1 4×10-20 cm2,and 274 5×10-20cm) than that in YAG and YLF,which,in practical,may loose the requirement for temperature tuning.The high energy transfer efficiency from Tm3+(up to 87%) and low pumping threshold(～15mW) show that Tm3+ can efficiently sensitizes Ho3+ for ～2μm emission in YVO4 crystal.The dependence of ～2μm emission for Ho3+ on the Tm,Ho doping concentration was preliminarily analyzed and discussed.In one word,Tm:Ho:YVO4 crystal may be a promising candidate for LD pump,compact,all solid state 2μm laser material.97|53|7更新时间：2020-08-11
- 摘要：One of the model theories for band aligning is average-bond-energy model,in which the average-bond-energy is used as a reference level for determining valence band offsets.Since the model has been proved quite successful in determining band offsets of lattice-matched heterojunctions,here we extended it to study band offsets of strained-layer heterojunctions.Through a careful study of band offset parameter E mv with deformation potential amv,we found that the averge band offset parameter Emv.av ( Emv.av=Em-Ev.av ) almost kept unchanged under different strain conditions,which is one of the main features of average bond energy method.Therefore,to obtain strained-layer band offset parameter Emv,only the unstrained band offset parameter Emv.O,deformation potential parameter b and the experimental value of spin orbit splitting Δ0 are necessary for simple algebraic operations.Obviously,it will be very convenient for calculating valence band offsets of strained-layer heterojunctions,since it doesn't need to consider the exact strain characteristics.In addition,we introduced deformation potential of band gap a Gap to describe the change of band gap under different strain states.Based on the relationship between conduction band offset and valence band offset (ΔEc=ΔEg+ΔEv),it is easy to calculate conduction band offsets of heterojunctions under different strain conditions.Our calculated band offsets of several common strained-layer heterojunctions are fairy good compared to those obtained by CNL or MST method,and in good agreement with experimental data.To sum up,our method is an effective and simple way in determining band offsets of strained-layer heterojunctions.关键词：band offset;average-bond-energy;heterojunction100|115|0更新时间：2020-08-11
- 摘要：The samples in this paper were synthesized by high temperature solid state reaction technique. The luminescence of the 4f5d states of Pr3+ doped in Sr2SiO4 and the characteristics of the energy transfer from Pr3+ to Gd3+ have been studied. In Sr2SiO4, the energy level of the lowest 4f5d band of the Pr3+ located at about 36000cm-1,which was much lower than that of the free ions, and was below the 1S0 energy level of the 4f2 configuration, so when excited into the 4f5d band, there was possibility to get the radiation transition of the 4f5d states. The energy gap between the lowest 4f5d band and the 3P2 level was about 14000cm-1,which was big enough that the non radiation from the 4f5d band to 3P2 level was so small,the radiation transitions from 3P0 and 1D2 level was unobserved, which indicated that the efficiencies of the 4f5d→4f radiative transition was high. From 0mol to 0.01mol of Pr3+ in Sr2SiO4, the emission strength became stronger with increasing the Pr3+ concentration. From 0.01mol to 0.03mol, the emission strength was almost constant,which was due to the concentration quenching of Pr3+ in Sr2SiO4. When excited by 240nm, the emission spectrum of Pr3+ was consisted of three bands, which was from 260nm to 440nm, the three peaks were at about 276, 318 and 396nm which corresponded to the radiation transition from the lowest 4f5d band to 3H4, 3H6 and 1G4,respectively. The excitation spectrum was from 200nm to 260nm, when employed Gaussian fit, three bands could be got, the peaks were at about 218,240 and 250nm, respectively. In Sr2SiO4, Pr, Gd, when excited by 240nm, the 311nm emission of Gd3+ was observed which could not be got in Sr2SiO4:Gd, the energy transfer from Pr3+ to Gd3+ happened. There were overlap between the transition of the 4f5d states to 3H 4 of Pr3+ and the absorptive transition of the Gd3+ 8S2/7→6I,so the 6I levels took part in the energy transfer process. Because the oscillator strength of the 6I levels was 10～20 times stronger than that of the 6P levels, the energy transfer from Pr3+ to Gd3+ was more efficient than that of only the Gd3+ 6P levels was included in the energy transfer process. When the concentration of Pr3+ was constant, the Pr3+ emission strength became weaker and the Gd3+ emission strength became stronger with increasing the Gd3+ concentration. When the Gd3+ concentration is bigger than 0.07mol,the concentration quenching happened and the Gd3+ emission strength decreased with increasing the Gd3+ concentration.关键词：Pr3+ ions;Gd3+ ions;4f5d state;fluorescent spectra;energy transfer99|55|0更新时间：2020-08-11
- 摘要：An ABA triblock conjugated polymer with strong two dimensional quantum confinement of excitons was synthesized by self-assembly of two block conjugated polymers in binary blends, the heterostructures were prepared. The spatial confinement of excitons,and microphase separation as well as efficient energy transfer via interchain and intrachain mechanisms in the ABA triblock polymer heterostructures were shown by optical absorption, photoluminescence, and photoluminescence excitation spectra of the triblock polymer at room temperature.关键词：conjugated polymer;quantum confinement effects;energy transfer129|105|1更新时间：2020-08-11
- 摘要：The white LED matrix was fabricated.The brightness,efficiency, color coordinate and color index were measured.The parameters of the white LED matrix were compared with that of Nichia. The maximum efficiency of 8.6lm/W was obtained under 300mA.While the current is less than 700mA, the efficiency is larger than 7lm/W. The change of color coordinate is very small and the color index is between 75 and 85, when the current changes from 100mA to 1000mA.关键词：white LED;color coordinate;color index105|117|1更新时间：2020-08-11
- 摘要：The organic thin film electroluminescence device with blue-green color using new organic material,silicon alkyl derivative(SCS-SiH),was fabricated. The structure of the device is Glass/ITO/PVK+SCS-SiH/Alp/Mg:Ag. The photoluminescence(PL) spectra of the film (SCS-SiH and PVK) were measured,which were illuminated by the different excitation wavelength of 406nm and 340nm,respectively. The PVK shows an emission maximum at about 420nm that corresponds to the result measured by others [7].The peak wavelength of SCS-SiH film is at 516nm with 70nm full width at half maximum(FWHM).The electroluminescence spectra were also measured and the peak wavelength of EL for the device is at about 500nm. It is found that the color of the device was blue-shifted with applied voltage,which may open vast vistas for full color flat panel display. The changing range is from 520nm to 495nm. The maximum brightness of the device is 810cd/m2 with 25V(89mA/cm2).关键词：organic electroluminescence;silicon alkyl derivative;blue shift of spectrum98|115|0更新时间：2020-08-11
- 摘要：In recent years,the properties of the surface polaron in polar crystals in a magnetic field have been of considerable interest.Larsen proposed a fourth-order perturbation method to calculate the ground state energy of two-dimensional polaron in a magnetic field.Wei et al. studied the cyclotron resonance mass and resonance frequency of the interface magnetopolaron using the Green's function method.The properties of surface polaron in a magnetic field have been discussed by linear combination operator method by the present authors and co-workers. In fact,so far research on the surface magnetopolaron was restricted to the approximation and calculation where the interaction of the surface electron with LO and SO phonons is considered,whereas the interaction of the surface electron with SA phonon is neglected.So far,the research on the quasi particle,the acoustic deformation potential (ADP) polaron,formed by the interaction of electrons with acoustic lattice vibration is very scarce. In this paper,the properties of the surface magnetopolaron interacting with the deformation potential in polar crystals,which has a weak coupling with surface optical phonon and surface acoustic phonon,are studied.The effective mass of the surface magnetopolaron interacting with the deformation potential in polar crystals is derived by using linear combination operator method.关键词：surface magnetopolaron;deformation potential;effective mass104|77|0更新时间：2020-08-11
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