最新刊期
卷 27 ， 期 4 ， 2006
- 摘要：In the development of silicon-based integrated optoelectronics,high efficient silicon-based light source is always the desired goal,however,the emission efficiency of silicon is very poor due to its indirect bandgap,saying nothing of stimulated emission.Then,many kinds of silicon-based materials system are explored to improve the emission efficiency of silicon, several important progresses have been made.Among the numerous silicon-based emission system,Ge/Si quantum dots is one of the approaches realizing siliconbased light-emitting devices due to its compatibility with standard CMOS processing and its wavelength covering the optical communication waveband,i.e,1.3~1.55μm.However,the emission efficiency of this material is very low,more and more attention is paid to improve its emission efficiency.If a photonic crystal is introduced into the nc-Ge/Si material,not only the spontaneous emission of this material but also the extraction efficiency of photons can be changed, resulting in a greatly enhanced emission efficiency.In this paper,two types of photonic crystal structures including point defect cavity and band-edge perfect photonic crystal are introduced to the Ge/Si quantum dots to enhance its efficiency,and the principle of the emission enhancement is analyzed from(theory.) For the 1.5 μm wavelength material,some structure parameters of photonic crystal are obtained.It can be seen from the simulated results that single point defect cavity can achieve single-mode operation very well,but the volume of active material within this kind of cavity is very small,the emission efficiency is very low,too.Coupled defect cavity and H2 cavity can increase the volume of active material included in the cavity.Moreover,comparing to H2 cavity,the number of resonant cavity modes reduces and the peak intensity of main mode increases for coupled defect cavity,which is more apt to improve the emission efficiency of Ge/Si(quantum) dots.Band-edge photonic crystal is more easily fabricated because its size is large and no defects are introduced.关键词：photonic crystal;photonic band gap;resonant cavity;nc-Ge/Si islands;quantum dots105|71|0更新时间：2020-08-11
- 摘要：In recent years,with the development of several experimental techniques,for example,molecular beam epitaxy and metal-organic chemical-vapour deposition,there has been of considerable interest in lowdimensional semiconductor structures such as quantum dots,quantum wells and quantum wires.There has been more and more interest in quantum dots due to novel physical property and extensive application prospects. In the past over ten years,many people studied the properties of a bound magnetopolaron in a parabolic quantum dot extensively by using many kinds of methods both theoretically and experimentally.In this paper,the influence of the temperature on the properties of weak-coupling bound magetopolaron in a parabolic(quantum) dot is studied.The vibration frequency,the ground state energy and the mean number of phonons of the weak-coupling bound magnetopolaron in a parabolic quantum dot are derived by using the linear(combination) operator and the unitary transformation method.The relations between the vibration frequency,the ground state energy and the mean number of phonons of the weak-coupling bound magnetopolaron with the temperature are discussed.Numerical calculations,for the CdTe crystal as an example,are performed and the results indicate that the vibration frequency of weak-coupling bound magnetopolaron in a quantum dot will(increase) with increasing the temperature,the mean number of phonons of weak-coupling bound magnetopolaron will increase with increasing the temperature and will increase with decreasing the vibration frequency of magnetopolaron.The ground state energy of the weak-coupling bound magnetopolaron will increase strongly with increasing the confinement strength of the quantum dot,and at the same position(same value of ω0),the higher temperature,the higher is the value of ground state energy.This is because crystal will be polarized more easily,LO-phonons will become manifold with the increasing of temperature.In this case,the interaction of electron and more LO-phonons makes the ground state energy and the mean number of phonons of the weak-coupling bound magnetopolarn increase in a quantum dot.关键词：quantum dot;bound magnetopolaron;temperature114|66|0更新时间：2020-08-11
- 摘要：As ones know,the polaron is a quasiparticle formed by an electron and phonons.Due to Coulomb interaction,the electron will make the lattice deformation take place,meanwhile,the deformation potential induced by the lattice deformation will exert on the electron,the electron-phonon interaction influence doubtless on the state of motion of an electron,for example,the energy band and effective mass of an electron could change by the interaction,the electron can also be trapped by the deformable lattice,therefore,the research on the polaron is very important in understanding optical and transport properties of a solid. Studying electron-phonon interaction has been a main subject in condensed matter physics;in experiments,the influences of the temperature on the forbidden-band width of semiconductors have been observed very early,with the increase of the temperature,the forbidden-band width of most semiconductors will narrow,but a few will widen,these situations are closely relevant to the electron-phonon interaction.In particular, recently ,a large amount of experimental results,ranging from infrared spectroscopy to transport properties involving the colossal magnetoresistance and high-Tc superconductivity,has pointed out the importance of the electron-phonon interaction,which has renewed the interest in studying the models of the electron-phonon coupled system,especially,the Holstein polaron,for its relative simplicity,is the most considered model for the interaction of a single tight-binding electron coupled to phonons. In the past several decades,the Holstein poloron has been studied in detail in one-dimensional lattices,various theoretical methods,such as variational approaches,the Global-Local variational method,the coherent -state expansion method,have been developed to study features of the Holstein polaron including ground-state energy,polaron energy band,effective mass and so on.However,so far,the work considering the influences of the temperature on features of the Holstein polaron is little still. The main aim of this paper is to investigate the influences of the temperature on the energy-band width and the effective mass of the Holstein polaron by using the canonical transformation method.It is shown that,at certain coupling strength,the energy-band width of the Holstein polaron will narrow and the effective mass will augment with the increase of the temperature,in particular,when electron-phonon coupling strength is big enough,the energy-band width will become zero rapidly in small region of temperature,in fact,the situation is rapid transition of the polaron from the energy-band state to the self-trapping local state,this is an interesting result obtained in the paper.It is obvious that these features of the Holstein polaron are very useful in explaining optical and transport properties of a solid.关键词：Holstein polaron;temperature;energy-band width;effective mass110|95|0更新时间：2020-08-11
- 摘要：With the development of the solid theory and experimental technology,the properties of the surface polaron in a crystal have been of considerable interest.Many investigators studied the properties of the surface polaron in many aspects by a variety of theoretical and experimental methods.Sak and Evans et al.studied theoretically the surface polaron in polar crystals for the first time.Gu et al.discussed ideal surface polaron and the weak,the intermediate and the strong coupling polaron in semi-infinite polar crystal.The properties of the surface polaron in polar crystal and the effective mass of a slow-moving surface polaron in a semi-infinite crystal are investigated using perturbation and linear combination operator methods by the present authors and co-workers,respectively.However,the research of these methods only was restricted to the case of crystals having only one mode of the longitudinal optical(LO) phonon.A large number of polar crystals,with several atoms per unit cell,have more than one LO phonon branch.For example,in cuprite such as CuO2 there are two LO phonon modes and for SiO2,GaAs1-xPx and a large number materials with perovskites structure(SrTiO3,LiNbO3,BaTiO3…) there are more than two modes.The polaron problem with many LO phonon branches has been studied by Matsura and Lepine.The properties of the polaron and the magnetopolaron in a polyatomic polar crystals are investigated by the present authors.However,so far,research of the properties of surface polaron in polyatomic crystals considering both the electron-bulk-longitudinal-optical(LO)-phonon and electron-surface-optical(SO)-phonon interaction,has been very scarce.The properties of the excited state of polaron in polyatomic semi-infinite crystal,which are the strong-coupling with bulk longitudinal optical phonon and surface optical phonon,are studied by using a linear combination operator and unitary transformation.Results show that when the election is infinitely close to the surface of the crystal,we can neglect the contribution of the LO phonons,otherwise,the distance between the election and the surface of the crystals is far more than the semi-diameter of the polaron;we must take into account the SO phonons effect,the LO phonons can be omitted.More commonly,when the distance between the election and surface is at the same magnitude grade of polaron's radii LO and so phonon's contribution must be studied at the same time.关键词：polyatomic semi-infinite crystal;linear-combination operator;polaron;first internal excited state;excitation energy115|60|0更新时间：2020-08-11
- 摘要：Since Haken first investigated the problem of exciton-phonon interaction in polar semiconductor,this field has been greatly studied by other theoretical and experimental methods.Current carrier is restricted at three directions therefore the superposition of hole-electron louds is greatly enhanced,and that lead to the strengthen of coulomb binding energy and oscillator strength,so the effect of exciton play a very important role in semiconductor quantum dot.For the complexing of the exciton's structure,a variety of theoretical model have been adopted to research exciton in semiconductor quantum dot.Such as,under the effectivemass appro-(ximation),the energy of the ground state and the binding energy of exciton have been calculated by literature in spheroidal,circular and cube quantum dots without considering the effect of the surface polaron.Lin and Zunger using PM method studied the band gap of spheroidal circular and gamma matrix in SI quantum dot.Xie,et al.studied the properties of exciton in semiconductor quantum dot by using the method of few-body physics.Yosuke Kayanuma and Lavanya,et al.discussed the quantum sizes effect of exciton in a spherical quantum dot by using variational calculational method.The effective Hamiltonian of weak and middle-coupling surface excitons of the pure 2D polar crystal are obtained by using Huybrecht's linear-combination operator method by Gu, et al.Under parabolic energy band structure,EMA method been mostly used for its intuition property.In this paper,within the effective mass approximation,the energy of the ground state in GaAs quantum dot is calculated by using linear-combination operator method and only considering the influence of the(electron)-phonon-weak coupling.The properties of exciton in parabolic semiconductor quantum dot are studied by using the methods of a linear-combination operator and unitary transformation.Within the effective-mass approximation,numerical calculations are performed for GaAs semiconductor.The result illustrates that for weak-coupling,the energies of the ground state of the light-hole and the heave-hole excitons will increase with the decreasing of the radius of quantum dot and increase with the increasing ω0 of the confinement strength.关键词：quantum dot;exciton;linear-combination operator;weak-coupling112|91|1更新时间：2020-08-11
- 摘要：The spray pyrolysis process was employed to synthesize the single host silicate phosphor,Ba3MgSi2O8:Eu2+,Mn2+.It was found experimentally that,its three-colour emission peaks situated at 608,500 and 437 nm respectively under excitation of 375 nm irradiation.The phosphor particle is in the size of around 4.5 μm.The effects of Al addition to the host on the microstructure and emission spectroscopy were investigated in details.The addition of Al ion to the host leads to a substantial change of intensity ratio between blue to green emission while the intensity of red-emission remains unchanged.Consequently,the parameters related to the white emission such as CIE coordinate,colour temperature can be adjusted by changing the amount of Al addition.Based on the modification of host microstructure of the silicate,the intrinsic effects of Al addition on the coordination number,ionic occupation and energy transfer were discussed.Theoretically,it has been well established,from classical silicate science,that the modification of the tetrahedral microstructure of Si-O by Al-ion addition could result in a great change of the properties(i.e.PL in our case) of the silicate host.There is some disputation,however,of whether the charge compensation or atomic configuration plays a key role to change the priority of the lattice occupation,crystal field around the different cations.The experimental facts in this work greatly support the fact that the impact of Eu ions situated at different lattices of Ba ions on the emission spectroscopy due to the disturbance of Al ion to the silicate network.Hence,this three-colour emission feature of this cost-effective silicate phosphor may become one of the important candidates for future high luminous efficiency white LEDs applications.关键词：silicate phosphor;pseudoboehmite;spray pyrolysis;WLEDs128|66|3更新时间：2020-08-11
- 摘要：Erbium-doped fiber amplifiers(EDFAs) with wide and flat gain spectra in telecommunication windows are the key issues for dense wavelength division multiplexing(DWDM) optical network systems.How-(ever),the traditional commercialized EDFAs are made of SiO2-based material in which Er3+ ions show a narrow (emission) bandwidth for the 4I13/2→4I15/2 transition.Many methods have been investigated to broaden and flatten the gain spectra of the traditional EDFAs in order to meet the capacity demand.Recently,tellurite glasses have received considerable attention in EDFAs for the broad bandwidth of over 70 nm,which meets the transmission capacity of DWDM systems.Nevertheless,the bad thermal stability and the high up-conversion become the(unsolvable) obstacle.Compared to tellurite,borate is a better glass-former compound and has higher(stability),larger phonon energy and broad bandwidth.We prepared Er3+ doped Bi2O3-B2O3-SiO2 glasses according to the following molar composition: 40% Bi2O3,20% B2O3,40% SiO2,and 3.0% Er2O3 is added to dope the glasses.The absorption spectra for Er3+ and OH-group,emission spectra and luminous decay for the transition 4I13/2→4I15/2 were measured.Accor-(ding) to the standard J-O procedure the intensity parameters for the Er3+ in the prepared glass were obtained.The concentration of OH-group and inner quantum efficiency for 4I13/2 level were estimated.It is validated that the lower quantum efficiency is caused by the higher content of OH-group,about 3 times of Er3+(content.) On the base of McCumber theory,the stimulated emission cross section for the 4I13/2 level was derived and found to be in better agreement with the results calculated by using the emission spectra.We draw a conclusion that it is essential for the borate used in EDFAs to decrease the higher content of OH-group despite of higher stability,larger phonon energy and broad bandwidth.关键词：Judd-Ofelt theory;quantum efficiency;McCumber theory;the four-level model;OH- content99|93|0更新时间：2020-08-11
- 摘要：In recent years,there has been a renaissance in the study of rare earth(RE) doped materials for applying in areas such as optical data storage,lasers,sensors and optical displays.Er3+ can originate the red and green upconversion emission under 975 nm excitation.The glass hosts with low phonon energy can reduce the nonradiative loss due to the multiphonon relaxation(MPR),therefore the choice of host material is quite important in the development of more efficient upconversion lasers.The intensity of red and green upconversion emission attribute to the absorption of Er3+,4I15/2→4I11/2(at around 980 nm),which present weak ground state absorption.The sensitization of Er3+ doped materials with Yb3+ ions is a well-known method for increasing the optical pumping efficiency.However,there has been a backward energy transfer when Yb3+ is more than certain concentration.So it is necessary to find the optimal doping concentration of Yb3+.The novel Er3+/Yb3+-codoped 45Bi2O3-45GeO2-10PbO glasses were prepared by the technique of high temperature melting in an electronic furnace.The absorption spectra and fluorescence spectra of Er3+/Yb3+-codoped 45Bi2O3-45GeO2-10PbO glasses were measured and investigated.The absorption near 980 nm becomes stronger with the increasing of Yb3+ concentration.The intense green(532 and 545 nm) and red(673 nm) emissions are observed at room temperature.The red(673 nm) emission is weaker than green(545 nm) emission while Yb3+ concentration is low,however it becomes much stronger when the Yb3+ concentration is high.The upconversion process involving the sequential two-photon absorption for the green and red emissions is analyzed. It is found that the optimal Yb3+ doping content is 2.5% when the Er3+ doping content is fixed at 0.5% according to the results of ET efficiency and upconversion fluorescence.The results suggest that this kind of glasses may be a suitable material for practical upconversion fiber optical devices.关键词：upconversion emission;energy transfer;bismuthate glasses107|60|2更新时间：2020-08-11
- 摘要：Much attention has been paid to search for high-efficient phosphor with the development of displaying device.Some commercial blue phosphors,such as BaMgAl10O17:Eu2+ do not meet the ever demanding requirements,they suffer decreasing performance of brightness and color quality because of the serious deterioration.New blue phosphor with stable hosts was belived to be a better way to solve this problem.In the(silicate) host series,Eu2+ appeared to be a feasible candidate for the blue emitting vehicle originating from(5d-4f)(around 420 nm) transition.SrAl2Si2O8:Eu2+,a potential excellent blue phosphors suitable for making PDP device and other luminescent apparatus,are conventionally prepared using solid-state reaction at high temperature.However,it is(difficult) to control over particles size and crystal structure at this condition,meanwhile the reaction temperature is so high,serious challenging problems arise to the equipment.Sol-gel method is one of the "soft" chemical methods,which have been employed successfully to prepare phosphor particles with better morphology and(operate) in a lower temperature,compared with solid-state reaction,in recent years.We reported the synthesis of the blue rare earth phosphor SrAl2Si2O8:Eu2+ by sol-gel method.The sol-gel method was adopted by reacting corresponding nitrate and tetraethylothosilicate(TEOS) at a 85℃ water bath to form a gel,from which the dried precursor was reduced at relatively low temperature of 921℃ to(generate) a blue fluorescence material SrAl2Si2O8:Eu2+.The product synthesized was characterized by thermogravimetry(TG),differential scanning calorimetry(DSC),X-ray diffraction analysis(XRD),and fluorescence spectrophotometry.Influential factors in the process of the sol-gel preparation,such as pH value,(ethanol) content,(amount) of citric acid,were studied in depth,and the optimal conditions for synthesizing SrAl2Si2O8:Eu2+ were determined.XRD analysis indicates that when the mole ratio between citric acid and metal ion was 1:1,the minimal amount of anhydrous ethanol sufficient to secure a total dissolution of tetraethylothosilicate was used,and the pH value between 1.0~2.0 was maintained,the pure SrAl2Si2O8 with hexagonal crystal phase could be obtained.The light emitting analysis showed that with the monitoring wavelength 463 nm emission the product gave an exited peak at 327 nm,and an incident light with wavelength 394 nm could generate a fluorescent light with emitting wavelength 468 nm from this phosphor.关键词：SrAl2Si2O8：Eu2+;sol-gel method;blue phosphor;Eu2+108|73|1更新时间：2020-08-11
- 摘要：Since the green long persistent phosphor SrAlO4:Eu2+,Dy3+ was reported in 1996,scientists(focused) their attention on rare earth doped aluminate,silicate or sulfide system.However,transition metal(ions),e.g.,Mn2+,which shows efficient luminescence and highly-saturated color in many compounds,can act as efficient emission center for luminescent materials.Zinc orthophosphate has three crystalline modifications,labled as α,β and γ crystal phases.The red long-lasting phosphorescent properties of β-Zn3(PO4)2: Mn2+0.05,M3+(M=Al,Ga) have been reported by J.Wang,however,the phosphorescent properties of γ-Zn3(PO4)2: Mn2+0.05,Ga3+ were not reported up to now. The preparation of γ-Zn3(PO4)2: Mn2+0.05,Ga3+ have two processes: firstly,the stoichiometric amounts of raw materials were thoroughly mixed and ground in an agate mortar.Then the mixtures were pre-fired at 500℃ for 3 h;secondly,the pre-fired samples were thoroughly reground again,then sintered at 850℃ for three hours under a thermal-carbon reducing atmosphere by solid-state reaction.The XRD spectra show that,when the concentration of Mn2+＞0.3%,quenching is contributed to the formation of β phase,but anneal is propitious to the formation of γ phase. The excitation and emission spectra show that,The three forms are excited at 234 nm(α),and 246 nm(β and γ),with emission peaks at 507 nm for α form,sharp peaks at both 507 nm and 616 nm for β,and sharp peak at 507 nm and weak peak at 616 nm for γ form.Both the two typical peaks are attributed to the(4T1→)6A1 transition of Mn2+.The emission color mostly depends on the coordination number(CN).The Mn2+ ion emits green light when is tetrahedrally coordinated(CN=4) in the lattice whereas it emits red light in(octahedral) coordination(CN=6). According to the long-lasting phosphorescence and decay measurement results,there is no long-lasting phosphorescent phenomenon in the α form,because there is no octahedrally coordinated Mn2+ in this structure.For the β and γ-ZPMG,the long-lasting phosphorescent emission band is also derived from the 4T1g(4G) →6A1g(6S) transition of Mn2+ in the host.The decay curves of β and(γ-ZPMG) can be divided into two processes: a fast and a slow one.After irradiated by UV lamp(254 nm) for 5min,the red phosphorescence of the Mn2+,Ga3+ co-doped β-ZPMG and γ-ZPMG are still observed in the dark for not less than 30 min and 15 min,respectively.关键词：phase conversion;red long-lasting phosphorescent materials;Mn2+;spectral properties94|128|2更新时间：2020-08-11
- 摘要：Aluminates activated by rare earth Eu2+ ion are new long lasting photoluminescence materials.These materials have recently attracted more attention due to not only their bright luminescence and super long afterglow without radioactivity but also the extensive application.The SrAl2O4:Eu2+,Dy3+ long lasting photoluminescence powders were synthesized by high temperature solid state reaction in a reducing(atmosphere).By using of low melt point alkali metal borophosphate glass as the basic glaze,SrAl2O4:Eu2+,Dy3+ powder and enamel glaze were mixed up homogeneously,and long lasting photoluminescence enamel coating was prepared by sintering the mixture on the substrate of aluminum alloy.The phosphorescence spectrum of the luminescent enamel is similar to that of the SrAl2O4:Eu2+,Dy3+ powder in both the shape and peak position,i.e.,a broad band with maximum emission intensity at about 515 nm.Therefore,the long lasting photoluminescence of the enamel is due to the 5d-4f transition of divalent europium.The effects of the amount of the doped phosphor,enamel thickness,sintering temperature and sintering period on the luminescence properties of the(enamel) coating have been investigated.It is observed that the phosphorescence brightness of the enamel is(improved) with that of the doped SrAl2O4:Eu2+,Dy3+ powder.And with the increase of the thickness of the(enamel,) the brightness of the enamel also increases.When the sintering temperature and the sintering time is(increased,) the brightness of the enamel will be decrease,which is ascribed to the destroying of SrAl2O4:Eu2+,Dy3+.Therefore,low melting temperature and short reaction time is of great benefit to improve the brightness of the enamel.Because the porcelain enamel has the characters of bright phosphorescence, long persistent(period) and smooth surface and so on,it is expected to be widely used in the field of advertisement board,(traffic) indicating board and building,etc.关键词：SrAl2O4：Eu2+;Dy3+;long lasting photoluminescence;enamel coating94|212|0更新时间：2020-08-11
- 摘要：Up-converting phosphors material(UPM) is the material that exhibits two-photon anti-Stokes luminescence by up-converting infrared to visible light.Recently there is growing interest in studying UPM because of their most promising use as fluorescent labels for the sensitive detection of cell and tissue antigens.In this field,UPM have many advantages: 1.permanent,strong,anti-Stokes emission of discrete wavelengths;2.unmatched contrast in biological specimens due to the absence of autofluorescence upon excitation with IR light;3.simultaneous detection of multiple target analytes;4.low-cost microscope modifications.When this material is applied to molecular biology,genomic research,virology,and microbiology,it has high potential value in diagnostic pathology,and may offer advantages for the detection of proteins or nucleic acids.Luminescent reporter molecules form an excellent alternative to radioisotopes and are increasingly used in research and clinical diagnostic assays.But in practice,the up-converting phosphors material unmodified have many problems,that is,easy to reunite and deposit,so they are unfit for fluorescent labels reporters directly.Few researches were done to modify this material to improve its stability in water.To enlarge the usage of UPM in fluorescent labels,a kind of up-converting phosphor material(UPM) surface modified with amido-(cyanogen) was prepared through liquid coating-sediment method.With isopropyl as solvent,we used 3-aminopropyltriethoxysilane to modify UPM at a definite temperature and a special substance as catalyst.The spectrum of FT-IR shows the new material has amidocyanogen.TG proves that non-modified material and modified material have different process of losing gravity.SEM finds that the dispersion of the surface modified material is better than that of the non-modified.The experiments show that the stability of the modified UPM is improved.Luminescence test shows that non-modified material and modified material have the same emit peaks but the intensity is much increasing.All these exprements show that a kind of modified UPM with amidocyanogen was prepared successfully.关键词：surface modification;up-converting phosphor material;amidocyanogen121|120|3更新时间：2020-08-11
- 摘要：Recently,ZnO has being paid more attention because of potential applications in ultraviolet light(emitting) diode and laser diode.However,it is very difficult to fabricate p-type ZnO due to serious self-compensation effect,which results in no great progress in p-n homojunction diodes.ZnO heterojunction as another route has been paid attention except the effort on the fabrication of p-ZnO.One attractive heterojunction is ZnO/GaN heterojunction because of similar crystal structure and small lattice mismatch of 1.8%.However,the emission of GaN plays a dominant role in the electroluminescence spectra of ZnO/GaN heterojunction light emitting diode.The main reason was analyzed,the new heterojunction was designed by introduced into MgO i-layer by plasma-enhanced molecular beam epitaxy(P-MBE),and n-ZnO/i-MgO/p-GaN heterojunction light emitting diode was fabricated.The electrical properties of each layer were determined by Hall effect measurement.The ZnO shows n-type conductivity with the carrier concentration of 1018cm-3 and the resistivity of 0.6Ω·cm.The hole concentration of p-GaN is about 1017cm-3.I-V curve show rectification diode behavior in this heterojunction and have turn-on voltage of 4V.The bright ultraviolet electroluminescence at 382 nm was observed in the room temperature electroluminescence spectrum.It is concluded that this emission is originated from the(recombination) in ZnO layer by comparing with photoluminescence spectra of ZnO and GaN.According to(Anderson) Model,it is proved that the injection of MgO layer can limit effectively electrons into p-GaN layer in this heterojunction due to very small electron affinity and wide energy band of MgO.It is very hopefull to (realize) the stimulated emission of ZnO using these heterojunctions by the improvement of(crystal) quality and the optimization of device structure.关键词：ZnO thin film;plasma-assisted molecular beam epitaxy;heterojunction;LED117|170|1更新时间：2020-08-11
- 摘要：ZnO,N-Al codoped ZnO,Zn0.81Mg0.19O,N-Al codoped Zn0.81Mg0.19O thin films have been deposited on Si(100) substrates as the precursory sources of Zn(CH3COO)2,Mg(CH3COO)2,NH4CH3COO and AlCl3 aqueous solutions using ultrasonic spray pyrolysis(USP) method.The crystalline structure,morphology images,electrical,optical properties and band gap of the films are characterized by X-ray diffraction(XRD),field emission-scan electron microscopic image(FE-SEM),Hall-effect measurement and photoluminescence(PL). The XRD patterns reveal that all the films are composed of wurtzite-type ZnO phase.No peak originating from other compounds is detected except those of ZnO.From the SEM images,we can see that all the films present good morphologic uniformity,smooth dense surface,no visible pores and defects over the film.Apart from that,there are some grain morphology differences between Zn0.81Mg0.19O and p-Zn0.81Mg0.19O films,perhaps due to the different nucleation modes resulted from different dopants.Hall-effect measurement results indicate that ZnO and Zn0.81Mg0.19O are n-type,while N-Al codoped ZnO and N-Al codoped(Zn0.81Mg0.19O) exhibit p-type conductivity.From the PL peaks of ZnO and Zn0.81Mg0.19O,it can be seen that Zn0.81Mg0.19O is tuned into shorten wavelength than pure ZnO.Furthermore,the photoluminescence peak of p-Zn0.81Mg0.19O film (exhibits) also blue-shift behavior from 378 to 356 nm compared with p-ZnO film.Accordingly,the band gap of p-Zn0.81Mg0.19O film increases with the Mg content increases compared with p-ZnO film.In addition,The growth rate dependence of electrical and PL properties in p-Zn1-xMgxO films are also(discussed.) Only upon moderate growth rate,the p-Zn0.81Mg0.19O film exhibits both good electrical and(excellent) PL(properties.) In conclusion,optimal growth conditions confirm that Zn0.81Mg0.19O films,both wide band gap and p-type conductivity,are successfully fabricated by codoping of N and Al using USP method,which are of(significant) importance for practical(applications) of Zn1-xMgxO p-n homojunctions and Zn1-xMgxO-based UV optoelectrical devices.关键词：USP;p-Zn1-xMgxO film;electrical properties;PL100|66|0更新时间：2020-08-11
- 摘要：Considerable attention has been paid to ZnO due to its wide direct band gap of 3.3 eV and large(exciton) binding energy of 60 meV at room temperature.Thus it becomes a promising material for ultraviolet light emitting diodes and lasers, transparent high power electronic devices and widely used in our community.In order to fabricate ZnO-based optoelectronic devices,both n-and p-type ZnO are needed.Undoped ZnO(exhibits) intrinsic n-type conductivity,and it is,therefore,difficult to achieve p-type ZnO because the fact that acceptors are compensated by various native donors,such as oxygen vacancies,Zn interstitial,and other(donors.) Except for the group-ⅴ dopants,Li is considered to be a shallow p-type impurity for ZnO.However,in practice it is still difficult to obtain p-type ZnO by Li dopant because Li substituting for Zn(LiZn) is metastable.Thus much attention has been paid on stability researches of p-type dopant in Li doped ZnO.The first-principles calculations were carried out with a powerful package called VASP(Vienna ab initio simulation package).The wave functions are expressed by plane waves with a cutoff energy 395.99 eV.Ionic potentials are represented by ultrasoft pseudopotentials with the Perdew-Wang 1991(PW91) GGA(genera-(lized) gradient approximation) correction.And 32-atom supercells were used to perform the total energy calcu-(lation.) Further,in order to improve the stability of LiZn in ZnO crystal,the geometrical and electronic structures of the different complexes of LiZn with native point defects were constructed and calculated.The calculated results show that some complexes of LiZn with native point defects can not only improve the stability and solubility of the defects,but also change their electronic structures.By comparing the stabilities and the related energy states of the complexes,OZn-LiZn complex has the lowest formation energy and also has shallow accept levels.It is suggested to be the best acceptor candidate for the p-type ZnO.But the formation of OZn-LiZn complex in practice is waiting for further investigations on crystal growth and device fabrication.关键词：ZnO;native defect;Li-dopant;first principles calculations108|81|2更新时间：2020-08-11
- 摘要：GaN and its related Ⅲ-Ⅴ alloys have received much attention in recent years for their potential ability in short-wavelength light emitting diodes,laser diodes and photodetectors.However,due to the lack of a suitable lattice-matched bulk substrate,they are usually grown on Al2O3 or SiC substrates with a high density of threading dislocations(TDs).The origin of these dislocations has been suggested to be due to a peculiar growth mode—mosaic structure which can be characterized by means of tilt and twist angles.For wurtzite GaN the mean tilt angle of mosaic structure is related to the FWHM of(0002) diffraction peak,which can be easily measured by using XRD.Unfortunately,the twist of lattice planes is difficult to be measured directly.High-resolution X-ray diffraction was used to determine the twist angle of mosaic structure in GaN epitaxial layers grown on sapphire by metal-organic chemical vapor deposition(MOCVD).Rocking curves of five planes were investigated,(0002);(1013);(1012);(1011);and(2021) respectively.Pseudo-Voigt function was used to simulate the rocking-curve of every plane.The twist angles of GaN layers were easily obtained by extrapolating the full width at half maximum(FWHM) of diffraction peak of the planes.The twist angles of the films measured directly by φ-scans of the(1100) reflection in grazing-incidence X-ray diffraction(GIXRD) agree well with the extrapolated results.As far as we know,it's the first time that the extrapolated method was checked to be valid in this material,and the results are useful for the further study of GaN films.关键词：GaN;mosaic structure;twist angle;GIXRD;X-ray diffraction100|90|0更新时间：2020-08-11
- 摘要：Vertical-cavity surface-emitting lasers(VCSELs) have obtained more attention over the past few years,due to many merits including high power,high efficiency coupling to fibers,high beam quality,ease to be integrated in arrays on single chip,and the low fabrication cost.Especially,high power VCSELs emitting at 850~980 nm are desired for optical communications,pumping solid-state lasers and Er-or Yb-doped(optical) amplifier.The proton implantation method is widely used in the VCSELs fabrication as a convenient and effective technology.The four-time proton implantation method is designed for fabrication of vertical-cavity surface-emitting laser array.This method can achieve the isolation between individual elements in arrays and current confinement in elements,respectively.Firstly,by using lower energy implantation on the top distributed Bragg reflectors to form the high resistance area's isolation between individual elements of the arrays;secondly through the higher energy implantation onto the upper layer of the active layers to form the high resis-(tance areas),the current confinements among the elements is confirmed.Through the analysis of the thermal interaction between individual elements in array devices,a simple theoretical model has been formed,and by using the transient thermal conduction function this kind of thermal interaction has also been studied.We(calculated) the thermal interaction efficient length in the different pulse durations.The one side thermal diffusion length,and the thermal interaction efficient length between two neighboring diodes in array were also(obtained) theoretically.In the experiment,through the four-time proton implantation method the 2×2 and 3×3 two-dimensional vertical-cavity surface-emitting laser array devices have been fabricated from the GaAs/AlGaAs multiple quantum well VCSEL epitaxial chips,and the characteristics such as near field,emission spectrum,and light output power have also been measured.From the measured lasing spectra results,there is no obvious difference in the lasing wavelength between element and array devices.For the light output power,the element device produces optical power of 2.66 mW,and it is up to 23.6 mW from the 3×3 VCSEL array device,which is almost the total sum of all elements in the array.Finally,We think that our study of the thermal(interaction) in 850 nm VCSEL array by using our thermal diffusion model could push the study of the thermal effect of VCSELs array device in other wavelength region.关键词：VCSEL;laser array;proton implantation.111|109|3更新时间：2020-08-11
- 摘要：Conducting polymers with highly extended π*关键词：octoxylphenylene-pyridine copolymers;optical properties;EL;energy gap93|102|0更新时间：2020-08-11
- 摘要：Copolymerization is one of effective approaches for preparation of high performance emitting conjugated polymers.The emission color of polyfluorene can be tuned over the entire visible region by different(incorporating) narrow-band-gap(NBG) comonomers into the polyfluorene backbone.So photophysical properties of fluorene-based copolymers strongly depend on NBG comonomers.Based on comparative studies for optoelectronic performance of copolymers(PFDNT) of 9,9-dioctyfluorene(DOF) and 4,7-di(thien-2-yl)-2,1,3-naphthothiadiazole and copolymers(PFHDNT) of 9,9-dioctyfluorene(DOF) and 4,7-di(4-hexylthien-2-yl)-2,1,3-naphthothiadiazole,it has been found that the photoluminescence efficiencies of copolymer PFHDNT are significantly enhanced due to incorporation of alkyl chain into NBG heterocycle comonomers reducing interchain interaction of copolymer PFHDNT.In comparison with copolymer PFDNT without alky substitution on both thiophene rings,copolymer PFHDNT shows blueshift photoluminescence(PL) and electroluminescence(EL) emission at the same copolymerization ratio as a result of the introduction of the long alkyl chain into the thiophene ring enhancing steric hindrance and reducing the energy of π-π*transition. Inaddition, the alkyl side chainin the 4 position of both thiophene rings can increase the NBG comonomer solubility in copolymerization reaction, thus themolecular weight of the resulted copolymers could be improved. On the other hand,the electrolum inescent efficiencies of those copolymers are not reduced because of incorporating alkyl chain into the NBG comonomers.关键词：flourene-based copolymer;narrow-band-gap commonomer;electroluminescence98|130|0更新时间：2020-08-11
- 摘要：White organic light-emitting devices(WOLED) have been attracting tremendous attention nowadays since from first being reported.They have many advantages such as their lightness and thinness,self light-(emission,) broad viewing angle,quick response,high efficiency,easy fabrication,low driving voltage,low(energy) consumption,low cost,etc.Therefore,they are becoming potential competitors in full color displays,backlights for liquid crystal displays and even next-generation of light sources.We fabricated a new type of white organic electroluminescent device using TBPe as blue fluorescent(dopant.) The configuration of the device is ITO/PVK:TBPe/Alq3:rubrene/Mg:Ag.In the device, PVK,Alq3 and rubrene are used as hole transport material,electron transport material and orange fluorescent dopant,(respectively).By adjusting the thickness of each emitting layer and the adulterated proportion properly,a white light with CIE coordinates of(0.26,0.33) was generated,which is located in the white-light region.The CIE coordinate stayed virtually constant when the voltage increased from 8 V to 16 V.The device had a(maximum)luminance of 738 cd/m2,a maximum external efficiency of(0.2%).For enhancing the brightness and chromaticity of the device,we attempted to use Zn(BTZ)2 instead of Alq3 as electron transport material.Bright white light,over 1300 cd/m2,was successfully obtained,and the maximum efficiency reached to(0.31)% at 8 V.In conclusion,the performance of the whole device was(increased) remarkably.We try to blend the polymer and small molecule organic material together as blue-light-emitting layer,which makes up the shortcoming for each other.The efficiency of white light-emitting is improved only by designing the device structure and changing the electron transport material reasonable.We make the device structure as simply as possible to satisfy the need of the practical use.关键词：white light-emitting;OLED;TBPe;Zn(BTZ)2110|115|1更新时间：2020-08-11
- 摘要：OLED(organic light emitting diode) is a very attractive candidate as display devices and for(various) applications.Since Tang et al.reported on organic electroluminescence devices,OLED has been widely studied by many researchers and developed as commercial products.Because OLED has a lot of merits from the viewpoint of mobile display such as low power consumption,light weight and thinness,many efforts are(being) made to develop a robust mobile display with OLED.At recent years,in order to improve OLEDs' luminescence-efficiency,much research has been done.However,improving carriers' recombination-efficiency is one of valid approach to improve OLEDs' luminescence-efficiency.Carriers' recombination-efficiency is connect with structures of devices and parameters of materials.So it is necessary to build a model of carriers' transport and recombination for finding out the relation between carriers' recombination-efficiency and the structure or parameters.In this paper,we attempt to build a model of carriers' transport and recombination on the classical bilayer OLEDs.In our experiments,a classical bilayer OLED(ITO/TPD/Alq3/Al) is fabricated by thermal evaporation method.We have test the property of the OLED.The result showed that the electricity-voltage relation accords with Fowler-Nordheim tunneling injection theory very well.Basing on Fowler-Nordheim's theory,analyzing the distribution of currents theoretically,and deducing mathematically,a model for carries transport and recombination on the classic OLEDs is presented.According to this model,we analyze carriers' transport and recombination process theoretically and probe into the expression of carriers' recombination-efficiency.Further more,under this model,a formula between the recombination-efficiency and the surface-density of charged carriers,including holes which congregate at the interface on the anode side and the electrons which congregate at the interface on the cathode side,is educed.In this formula,the macroscopic variable (carriers' recombination-efficiency) is expressed by microscopic variables(surface-density of charged car-(riers)).It can offer some theoretical foundation for improving the efficiency of charged carriers recombination in OLEDs from microcoscopic mechanism.关键词：OLEDs;model of carriers' transport;potential barrier of interface104|57|0更新时间：2020-08-11
- 摘要：With their ionic side groups being attached to the conjugated main chain,conjugated polyelec-(trolytes)(CPs) can offer particular properties compared with the normal "neutral" polymers,having attracted considerable attention in recent years.Generally speaking,there are only a few reports on electroluminescent properties of LEDs fabricated from CPs.Previously,our group has reported the first LEDs based on ammonium functioned polyfluorene electrolytes,and a series of high-efficiency,environment-friendly electroluminescent polymers.With their terminal amino groups and quaternized ammonium groups,the devices from such polymers show the excellent electron injection ability.As a good performance of a device requires the balance between the hole and electron transporting in the emissive layer,it can feasible to synthesize polymers containing hole-transporting units on the basis of our previous work.It is well-known that carbazole-containing polymers are good hole-transporting materials due to the electron-donating capabilities associated with the nitrogen in the carbazole.A series of novel aminoalkyl-substituted fluorene/carbazole based main chain copolymers with benzothiadiazole(BTDZ) of different content were synthesized by Suzuki coupling reaction: poly[3,6-(N-(2-ethyl-(hexyl))carbazole)-(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-4,7-(2,1,3-benzothiadiazole)](PCzN-BTDZ).Through a postpolymerization treatment on the terminal amino groups,their quater-(nized) ammonium polyelectrolyte derivatives were obtained: poly[3,6-(N-(2-ethylhexyl)carbazole)-(9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)propyl)-2,7-fluorene)-4,7-(2,1,3-benzothiadiazole)] dibromide(PCzN-BTDZBr).It was found that devices from such polymers with the high work-function metal(cathode) such as Al show similar device performance to that by using the low work-function cathode such as Ba,indicating the excellent electron injection ability of these polymers.And it was observed that the efficient(energy) transfer occurs by exciton trapping on the narrow band gap BTDZ site for both the neutral and the(quaternized) copolymers.The addition of BTDZ comonomer also improves their PLED devices performance.When PEDDT/PVK was used as an anode buffer,the external quantum efficiency of the copolymer PCzN-BTDZ1 is 0.99%,which is higher than that of the copolymer PCzN in the same device configuration.关键词：conjugated polyelectrolytes;electroluminescence;carbazole;fluorine113|81|1更新时间：2020-08-11
- 摘要：Organic light-emitting diodes(OLEDs) are of great interest,since they efficiently emit light in the visible region and give promising applications.Full color displays require pure red,green and blue emission.However,the broad nature of the luminescent spectra of these organic molecules leads to the poor luminescent purity,which is dull and,thus,not suited for actual display applications.Rare earth complexes are very suitable for full color displays because of their sharp emission bands.In addition,EL efficiency based on rare earth complex is not limited by spin ruling,since their photoluminescence results from the formation of both singlets and triplets of the ligands,and then transferring energy to lanthanide cores.Theoretically,the upper limit of inner quantum efficiency can reach 100%,which is four times higher than that of the devices using other fluorescent material.For OLEDs,the development of high-perfor-(mance) red emission is still much in demand compared with both green and blue emission.A new organic complex of rare-earth europium(Eu) EuL1L2 was reported.The electroluminescence and photoluminescence of this Eu complex were studied.The multilayer devices with the structure of ITO/PVK:PBD:EuL1L2/PBD/Alq3/Mg:Ag/Ag were fabricated,using PVK:PBD:EuL1L2 as emitting layer,PBD as(exciton) block layer,and Alq3 as electron transporting layer.The emission from electron transfer layer was easily seen because the lifetime of exicton of Eu complex.In the experiment,a electron transfer material PBD was used as exciton block layer.Alq3 emission intensity become weaker than that of Eu complex,with the increase of the exciton block layer PBD thickness.As the block layer 80 nm,a pure red light with a peak of 612 nm and a half bandwidth of 10 nm,attribute to the(emission) of trivalent europium,was observed clearly.The assignment of the emission bands is referenced to(analogous) complex: 576 nm(5D0→7F0),590 nm(5D0→7F1),612 nm(5D0→7F2),652 nm(5D0→7F3),700 nm(5D0→7F4).The CIE coordinates of resulting emission was(0.608,0.339),a maximum luminescence brightness of 20cd/m2 and external quantum efficiency brightness of 0.09% were achieved.关键词：OLED;Eu complex;red light;exciton block layer85|136|1更新时间：2020-08-11
- 摘要：The synthesis method of OXD-7 was studied chiefly.Its synthesis step as follows: 1.Ethyl 4-tert-butylbenzoate can be prepared by the esterification reaction of 4-tert-butylbenzonic acid and ethyl alcohol,then it was reacted with hydration hydrazine to get 4-(t-butyl)benzoyl hydrazine;2.m-phthaloyl chloride was prepared by the reflux reaction of isophthalic Acid and thionyl chloride;3.4-tert-butyl benzoyl hydrazine was added to the synthesized m-phthaloyl chloride.The mixture was(allowed) to react at 80℃ for 2 h,then the mixture was cooled and then poured into ice-water.The precipitate was filtered and washed with water,dry in 100℃,the previous compound of OXD-7 was prepared.Finally,the previous compound of OXD-7 was put into the three-necked bottle,POCl3 and PCl5 was added,heats to reflux for 5 h,the phosphorous oxychloride was removed by the distillation under a reduced pressure,filters,the residue was washed with water and recrystallized two times from ethyl alcohol to give 11.2 g of OXD-7,the purity is 97.2% by HPLC.The sublimation of OXD-7 was executed under the pressure of 35 Pa and the(temperature) of 300℃ used the sublimation system designed by ourselves.After the sublimation,the purity of OXD-7 is 99.2%,the melting point is 241.5℃.A blue organic electroluminescent device was fabricated and its structure is ITO/CuPu/NPB/OXD-7/Alq3/Mg-Ag/Al.An indium-tin-oxide coated glass substrate (anode substrate) was sequentially washed in a cleaning solution,rinsed in deionized water and dried.Copper phthalocyanine(150),N,N′-bis-(1-naphthyl)-N,N′-diphenyl benzidine(600),OXD-7,alumium-tris-8-hydroxyquinoline(350)were vapor deposited in turn on the ITO glass,then Mg-Ag alloy was vapor deposited as the anode,finally,metal aluminum was vapor deposited onto the Mg-Ag alloy as the protecting layer.The device was packaged in a dry glove box full of(nitrogen) for protection against ambient environment.The photoelectric property and life-time of OXD-7 were tested.The influence of the material purity to the lifetime and the brightness was studied and discussed.Under 8 V drive voltage,the device gives a blue emission peaked at 472 nm,the maximal brightness is about 456 cd/m2,the CIE coordinate of the emission color is x=0.144 4,y=0.098 1.关键词：blue organic electroluminescent material;OXD-7;OELD;1;3-di(4-t-butylphenyl-1;3;4-oxadiazole)benzene126|120|5更新时间：2020-08-11
- 摘要：The hole-blocking characteristics of organic light emitting materials DPVBi were discussed.The(device) structure included indium tin oxide glass(ITO) substrate/N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′diamine(NPB) as hole transparent layer/DPVBi as emitting layer/40 nm tris-8hydroxyquinoline aluminum(Alq3) as electron transport layer/0.5 nm LiF/100 nm aluminum(Al).Organic materials were deposited by vacuum deposition at 1.33×10-4 Pa using resistively heated tan-(talum) and quartz boats.The doping was carried out using the co-evaporation method.The layer thickness of the deposited material was monitored in situ using an oscillating quartz thickness monitor.Finally a LiF buffer(layer) and Al cathode were deposited at a background pressure of 1.33×10-4 Pa onto the organic films.EL spectra and CIE coordination of the devices were measured by PR650 spectra scan spectrometer and the current-voltage-brightness characteristics were simultaneously measured by a Keithley 2400 programmable voltage-current source.All measurements were carried out at room temperature under ambient conditions.The experiment results show that the hole-blocking characteristic is related to the DPVBi thickness and the NPB thickness.While NPB thickness is less than DPVBi thickness,the hole-blocking capacity of DPVBi increases as DPVBi thickness (increases).The hole-blocking capacity of DPVBi decreases as NPB thickness increases when the DPVBi thickness is unchanged(120 nm).While NPB thickness is more than DPVBi thickness,the hole-blocking capacity of DPVBi increases as their thickness difference increases.The hole that through the DPVBi layer into the Alq3 layer increase,causing the full width at half maximum(FWHM) of the emission spectrum is broaden.In the conclusion,when DPVBi was used to fabricate the organic blue-light device in order to ensure the luminance and efficiency of the device,the exciton in DPVBi layer should be limited,the emission of Alq3 should be controlled,the FWHM of emission spectra should be decreased,and the chroma of device will be improved.As far as organic white-light device is concerned,the thickness difference between NPB and DPVBi should be controlled when the total thickness of device is less than 100 nm.The method we adopted enables the emissions of each kind of material to achieve equilibrium and the performance of the organic white-light device can be improved obviously.关键词：organic light emitting materials;hole;hole-blocking characteristics125|86|5更新时间：2020-08-11
- 摘要：Scanning probe microscopy offers the possibility of probing physical properties with high spatial(resolution).In particular,scanning tunneling microscopy(STM) and scanning tunneling spectroscopy(STS) can be used to combine structural characterization with probing the electronic signature of the organic compounds on a molecular scale.A number of STS investigations on organic materials have been published in(recent) years.And most of the authors observed electron transport through the frontier orbitals of the organic molecules(i.e.,through the highest occupied molecular orbital(HOMO) and the lowest unoccupied mole-(cular) orbital(LUMO).The measurements of the contributions of the second filled and second unfilled molecular orbitals to the tunneling current have also been studied in a few researches.Compared with other methods of molecular energy structure characterization,such as Ultraviolet-Visible Spectrophotometry(UV-Vis),(Cyclic) Voltammetry(CV) and Ultraviolet Photoelectron Spectroscopy(UPS),STM/STS can show the nano-sized surface microscopy of the molecule in real time and the detailed information of surface roughness and graininess of the thin solid film can be obtained.The STM/STS measurement has become a powerful tool for the study of nanostructures in numerous areas of science and technology.The application of STM/STS in the field of(organic) light-emitting diodes(OLEDs) is promising.We present here a study of vapor deposition thin film(layers) of tris(8-hydroxyquinolino) aluminum(Alq3), 4-(2-(3,3-dicyano-methylene-5,5-dimethyl-1-(cyclo)-hexylidene)vinyl)phenyl(1-naphthyl)phenyl-amine(DPN-2CN),and 4-(2-(3,3-dicyano-methylene-5,5-dimethyl-1-cyclohexyl-idene)vinyl)phenyldi(1-naphthyl)-amine(DNP2CN) on the substrate of ITO.The surface electronic structures of organic light-emitting materials Alq3,DPN-2CN and DNP-2CN were studied by STM/STS.The obtained ELUMO of compound DPN-2CN were 3.50 eV and 3.51 eV respectively.And the(energy)-band parameters of DPN-2CN and DNP-2CN were determined by comparing their surface electronic structures with Alq3.The energy-band parameters of DPN-2CN and DNP-2CN obtained from the above method was compared with the result of CV experiments.The ELUMO obtained from CV experiment is 3.68 eV for compound DPN-2CN,and 3.69 eV for compound DNP-2CN respectively.The result of STM/STS was basically in accordance with that of CV.关键词：organic light-emitting material;STM;STS;electrochemistry;cyclic voltammetry87|145|0更新时间：2020-08-11
- 摘要：Rare earth complexes have become excellent luminescence materials,this is related to lanthanide(ions') peculiar characteristics,and have potential use in laser,photoluminescence and electroluminescence.Rare earth complexes with aromatic carboxylic acids are a kind of luminescent materials with good properties. So much attention was paid to the fluorescence properties of these complexes.There are some reports about fluorescence properties of the complexes of a part of rare earth with phthalic acid and terbium with benzoic acid and salicylic acid.However,no report on systemic study of the fluorescence properties concerning rare earth complexes with different aromatic carboxylic acids has been reported.For this purpose,we have synthesized fourteen complexes of Sm,Eu,Tb,Dy with benzoic acid derivatives: RC6H4COOH(R=o-NH2,H,p-NH2,(o-OH),m-Cl,o-COOH,m-COOH,p-COOH,p-OH,m-NO2,3,5-Dinitro,p-Br,o-I,2-OH-5-SO3H)and it is found that the complexes of Sm and Dy with these aromatic acids show little fluorescence,but Eu and Tb with some of these aromatic acids show strong fluorescence under the excitation of UV,and that the complexes of terbium with sulfosalicylic acid have the strongest fluorescence intensity.In the present paper,terbium complexes with aromatic acids were synthesized and their fluorescence properties were investigated.The synthetic process was as follows: The aqueous TbCl3 solution was slowly added to ligand solution(according) to the molar ratio of Tb3+:ligand=1:3 or 2:3(phthalic acid,m-phthalic acid) at 80℃ under(stirring.) The pH of the mixture was adjusted to 6.0～6.5 by addition of sodium hydroxide solution.Thus,white precipitates of the complexes came into being.After another two hours,stop stirring,the mixture was cooled to room temperature.The white precipitates of the complexes were filtered,washed with deionized(water) and ethanol till no chloridion could be found, then dried at 85℃ under vacuum for 4 h.The compositions of samples were identified by elemental analyses.UV,IR of the complexes also have been investigated.The UV spectra indicated that the complexes' ultraviolet absorption was mainly the ligands' absorption,but the location of peak drifted.The IR spectra showed that the IR spectra of complexes are dif-(ferent) from those of free ligands and the band at 400～500cm-1,due to the stretching vibration of Tb-O,is absent for free ligands.The fluorescence properties were investigated by using luminescence spectroscopy,the results showed that all the six complexes of terbium exhibited excellent luminescence,due to the transition from the lowest excited state 5D4 to 7FJ ground state manifold,and the complexes of terbium with sulfosalicylic acid had the strongest fluorescence intensity.关键词：rare earth;terbium;benzoic acid;fluorescence;complexes105|217|1更新时间：2020-08-11
- 摘要：Delayed fluorescence(DF) is the luminescence phenomenon of plant photosynthestic apparatus(after) stop illuminating,it is also called delayed light emission(DLE) for that it has the same wave with fluorescence and is delayed after fluorescence.DF is not only the internal fluorescence probe for the efficiency of charges separation in the P680,but also the useful implement to distinguish that photosynthesis produced on(antenna) or on electron transfer chain,hence,it is used widely in study on the photosynthestic capacity of plant and on the stress effects of environment on plant.Research of the mechanism for delayed fluorescence origin plays an important role in the application of DF.Based on the Charge Recombination Theory(CRT),the mechanism for delayed fluorescence origin is theoretically analyzed in this paper.The decay kinetic equation of DF can be well fitted by poly-exponent.We postulated that constant "C" is a symbol for component of delayed fluorescence,whose lifetime is more longer than other component,and it is come form the backward transport electron from PSⅠto PSⅡ and the recombination of P680+.Fortunately,we successfully and firstly testified that the third component(constant C) with lifetime(τ>5s) much greater than the time of the registration period(which is presented as a constant),is corresponds to the backward transport electron from PSⅠand the recombination of P680+.The experimental evidence has significance on the study on the mechanism for the delayed fluorescence origin of higher plant chloroplast,it also provides a quantitative analysis standard for the rapid dermination of the photosynthestic rate of plant by using plant light-induced delay fluorescence.关键词：delayed fluorescence;long-lifetime component;charge recombination;election back-transportion;chloroplast122|79|0更新时间：2020-08-11
- 摘要：Fiber optical biosensor is a significant kind of modern biosensor systems.At present,many fiber optical biosensor systems depending on detecting fluorescence have been on sale,but they almost obtain the bio-informatics by the intensity of fluorescence which comes from the fluorescent indicator.On the other side,the fiber optical biosensor systems that could get the bio-informatics directly from the self-fluorescence(spectrum) of biologic samples have not come into the market.In this situation,the author started some research on the samples of fresh human breast tissues by a self-made three-dimensional fluorescence fiber optical(spectrometer.) With the results,it's found that there are many obvious differences in the self-fluorescence(spectrum) between the normal and cancerous tissues.In details,the peak value in normal tissue is on the(position) of 511 nm,while it is on the position of 513 nm around the cancerous tissue,518 nm in the core of cancerous tissue.We can observe that the position of peak value has a trend to shift to red side from normal to(cancerous) tissues.On the other side,the intensity ratio of two primary peaks in normal tissue is 0.77,while it is 0.64(around) the cancerous tissue and 0.58 in the core of cancerous tissue.We can observe that there is a decreasing trend from normal to cancerous tissues.Furthermore,the source of the spectral difference and the origin of different fluorescent bands are analyzed.Although there are still much work to do and lots of elements to reveal,it is definitely obvious that the fluorescence spectrum technique combined with fiber optical sensors technique would make great progress in on-line diagnosis of human cancer in near future.关键词：biosensor;fiber optical biosensor;fluorescence;self-fluorescence spectrum110|105|1更新时间：2020-08-11
- 摘要：In recent years,there has been considerable interest in the study on the luminescence enhancement effects of the rare earth complexes.An effective approach to increase the luminescent efficiency is to modify the complexes with different kinds of counter ions,such as Cl-,NO-3,ClO-4.Another way is to mix certain anion rare earth ions,such as La3+,Gd3+,and Y3+,could significantly enhance the luminescence intensities of the complexes of Eu3+,Tb3+,and Sm3+.In order to study the luminescence enhancement effects of anion ions,a series of europium complexes of 2-thiopheneglyoxylic acid(HL),o-phenathroline(phen) and triphenyl phosphine oxide(TPPO) with different molar ratios of Eu3+ to Y3+ and Gd3+ have been synthesized.The luminescence spectra were taken on WGY-10 fluorescence spectrophotometer.Enhancement of Eu3+ fluorescence in Eu-L-phen complex system has been observed by addition of Y3+ and reach maximum when the molar ratio of Eu3+:Y3+ is 0.7:0.3.Then the(luminescence) intensity of the complexes decreases with a further increase of the Y3+ content.Concluded from R=It/Ip(It=theoretical values of the fluorescence emission intensity,Ip=practical values) is all above(1.0).When Y3+ ions added to Eu-L-TPPO complex system,weak sensitization even extinguishment to some extent could be observed.In this system,R values of each complex approach 1.0.When a little amount of Gd3+ ions added to Eu-L-TPPO complex system,it can extinguish the fluorescence intensity.R values are(below) 1.0 when molar ratio of Eu3+: Gd3+ is 1:06:4,only the R value for peaks at 699 nm is 1.3 when molar ratio of Eu3+:Gd3+ is 6:4.But adding a large amount of Gd3+ ions can sensitize obviously.This kind of luminescence enhancement due to the energy transfer process between ligands and lanthanum ions.The luminescence enhancement effects of counter ions(NO-3,Cl-,ClO-4) were also studied.In binary complexes,the fluorescence intensity of chloride system is the largest of all,and that of nitrate system the(largest) in ternary complexes.Luminescence properties of lanthanide ions could be great influenced by the(geometry) of their complexes,respectively.关键词：europium;inert lanthanide ions;counter ions;2-thiopheneglyoxylic acid;fluorescence spectra126|134|1更新时间：2020-08-11
- 摘要：The inhibition and enhancement of liquid phase CL by organic compounds are of considerable(interests) in analytical chemistry because they can be used for the sensitive detection of numerous compounds.However,the mechanism of inhibition and enhancement is not fully understood and the discovery of new(enhancers) and inhibitors is usually achieved in an empirical fashion by trail and error.Although there are(reports) in the literatures concerning the use of the luminol-KIO4-H2O2 CL for the determination of hydrogen peroxide,glucose and ascorbic acid,the effect of aromatic compounds on the luminol-KIO4-H2O2 CL has not been studied systematically.The effects of 36 organic compounds on the luminol-KIO4-H2O2 system chemiluminescence(CL) were studied under different pH conditions of luminol solution.The CL signal was detected with a flow injection chemiluminescence system(Xi'an Ruimai Electronic Technology Co.,Ltd.,China) consisted of a model IFFM-D peristaltic pump,a mixing tee,a model IFFS-A CL detector equipped with a glass coil(used as reaction coil and detection cell),a photomultiplier,and IBM compatible microcomputer.It was found that most of the tested compounds could inhibit or enhance the CL intensity.The activities of such(inhibitors) or enhancers were related to pH value of the CL system and the number and position of functional groups such as —OH and —NH2 on aromatic ring and property of substituent group,electron delocalization and steric hindrance.The CL spectra and UV-visible absorption spectra were studied and the mechanism for the CL inhibition and enhancement was also discussed.The mechanism for such inhibition or enhancement of organic compounds is most likely due to the reactions between inhibitors or enhancers and radical intermediates of the CL reactions.Based on the CL inhibition or enhancement,the possibility of analytical applications was explored.The results demonstrated that numerous compounds are detectable at ng·mL-1 level.关键词：organic compound;chemiluminescence;luminol;enhancer;inhibitor102|143|0更新时间：2020-08-11
- 摘要：ZnO,as a wide direct bandgap and large exciton binding energy semiconductor material,has stimulated great interests because of its promising application in ultraviolet optoelectronic devices,ultraviolet light-emitting diodes and ultraviolet laser diodes.Nanostructural ZnO is beneficial to increase the exciton recombination probability and to lower the pumping power threshold due to the high state density near the band edge.The research progress on ultraviolet spontaneous emission and stimulated emission of nanostructure ZnO is(reviewed) mainly based on some novel morphologies which were fabricated in our experiments by vapor phase transport(VPT) processes.For a ZnO nanostructure with good crystal quality,the photoluminescence presents a strong ultraviolet band emission originated from the band-edge excitonic recombination.The perfect crystalline nanostructure with strong UV spontaneous emission is required for ZnO nanolaser.In our experiments,the ultraviolet amplified spontaneous emission(ASE) has been observed in ZnO nanofiber network(arrays) with 6-symmetry structure fabricated on a catalyst-patterned substrate.The UV light was gained in the network arrays and amplified gradually duo to the nature wave guide properties of the ZnO nanofiber branches.When the pumping power is high enough,ASE happened.The UV laser of ZnO have been obtained in three type of resonant cavities,random cavity,Fabry-Perot cavity and whispering gallery mode(WGM) cavity.In our research,ZnO microtubes have been employed as F-P cavity and a UV stimulated emission signal has been obtained and analyzed,which is similar to the phenomena in nanorods,nanobelts and nanocombs reported by other researchers.It is noted that a novel structure of ZnO,single crystal nanodisk has been fabricated in our experiments.It is expected to be as WGM cavity with low loss,low threshold and high quality factor.关键词：ZnO;nanosized material;photoluminescence;UV laser113|101|3更新时间：2020-08-11
- 摘要：Quasi-one-dimensional semiconductor nanomaterials have been stimulated a lot of interests for scientific research due to their unique physical and chemical properties and their potential applications in mesoscopic physics and nanodevices study.Among them,ZnO is one of the most promising oxide semiconductors.It has a direct wide band gap(3.37 eV) and a large exciton binding energy(60 meV).So it becomes a focus material for studies in short wave semiconductor laser nanodevices and visible photoelectronics devices.ZnO tetrapod nanostructures were synthesized by thermal evaporation of Zn powders under different flow rate of argon at 150,180,240 sccm,respectively.Scanning electron microscope(SEM),transmission electron microscope(TEM) and photoluminescence(PL) were employed to determine the morphology and optical properties of the products.The results showed that argon gas flow rate influence on the ZnO morphology significantly.With the increasing of argon gas flow rate ZnO nanostructures changed from variety of nanostructures,including tetrapods,nanowires,nanosheets and nanodendritics to single uniform tetrapod nanostructure.The luminescence properties show that the emission intensity changes evidently along with the change of argon flow rates in the tube.The luminescence properties show that the UV emission become weaker and the blue emission become stronger,namely the ratio of the blue emission to the UV emission become bigger with the increasing of the argon flow rate.It is suggested that the oxygen vacancy is responsible for strong blue emission. The supposition is confirmed by the results that the blue light emission peaks disappear after the products are oxidized annealing in air at 700℃ and the blue light emission peaks appear again after the oxidized products are deoxidized annealing in H2 at 700℃.Our experimental results provide the proofs that the blue light emission of nano-ZnO originates from oxygen vacancy.The experimental results are helpful for understanding the mechanism of the blue-green emission of nano-ZnO.Our investigations are significant in providing an effective way to enhance the intensity of blue light emission for various applications.关键词：thermal evaporation;tetrapod nanostructure;photoluminescence;oxygen vacancy108|90|3更新时间：2020-08-11
- 摘要：PbS nanoparticles embedded in SiO2 thin films were prepared by the sol-gel method and the dip-coating technique.The sample under investigation was PbS nanoparticles sol-gel film about 150 nm thick on glass substrate,its linear absorption spectrum indicate the band gap shifts to higher energy for PbS nanopar-(ticles) due to the quantum confinement effect.The absorption spectrum of sample exhibits a distinct band(peaked) at 640 nm,which is attributed to 1Se-1Sh transitions.An average particle diameter of 5 nm was(estimated) according to a simple effective mass approach.We report on the nonlinear optical properties(NLO) of PbS nanoparticles at various excitation densities.At low excitation densities,the OKE response evolution of PbS nanoparticle,including a positive component and a negative component,and a very slow decay was(observed.) At higher excitation densities,there is a pronounced modification of the temporal profile,the disappearance of the positive component and the existence of the negative component.The results indicate that the ultrafast optical nonlinearity arises from the contribution of the absorption saturation due to exciton transition and the photo-induced absorption due to biexciton effect.The contribution of the one-exciton state and that of biexciton to the third-order susceptibility are opposite,which agrees with Banyai's theoretical prediction.At excitation density of 4mJ/cm2,the magnitude of for PbS nanoparticles doped SiO2 thin film is calculated to be 5.1×10-10 esu, which arises from the contribution of biexciton effect at high pump intensity.The magnitude of for PbS nanoparticles is four orders of magnitude larger than that of CS2.And it is one order of magnitude larger than that of the standard optical nonlinear material CdS(5×10-11 esu).Based on the preparation method of our samples,size distribution of the nanoparticles is usually more than 10%.Wide size distribution results in a strong reduction of the optical nonlinearity.If we can obtain the sample with a narrow size distri-(bution) and high-doped concentration,the optical nonlinearity may be further increased.关键词：PbS nanoparticles;third-order optical nonlinearity;femtosecond optical Kerr effect103|135|0更新时间：2020-08-11
- 摘要：Organic light-emitting diode has been emphasized and regarded as one of the best technologies of flat panel displays for its many advantages,such as low-voltage driving,low power dissipation,wide visual angle,thin and light-weight and so on.We want to introduce the full process of designing the AMOLED,which includes three sides content.Firstly,simulations using poly-TFT SPICE models are performed on the pixel driving circuit of a 2 inch(5.08cm,64×3×80) AMOLED panel,and on its substrate some peripheral driving circuits are integrated.The results are evaluated and analyzed,and confirmed the driving voltage and current of RGB OLED pixels while the color AMOLED is in white balance.At the same time,through the simulation we can find that the circuit can keep the current very well in the voltage range we confirmed,this means that if we provide the proper voltage the OLED panel can display high quality images.Secondly,we mention a means to make the image data for OLED panel displaying.This means encodes the BMP data to fit our design,and then puts the encoding file into E2PROM,to prepare the picture data for peripheral driving circuitry.At last the peripheral driving circuitry is designed based on FPGA and TFT-LCD chip.Through the simulation we can confirm that the peripheral driving circuitry can complete the driving OLED tasks.Now the OLED driving ASIC is few and expensive,however the TFT-LCD driving circuit is very mature and cheap.So if we can utilize the TFT-LCD driving circuit to design the OLED driving circuit,that is a very meaning thing.In the TFT-LCD driving chips, it integrates the shift register,the buffer,the latch,and inner D/A,at the same time it can output 256 gray level driving voltage.So using it not only reduces the complexity and periods of developing peripheral driving circuitry but also enhances the stabilization of peripheral driving circuitry and more existed TFT-LCD driving chips can exert more use in OLED driving circuit design.From the result we can prove that the model of using TFT-LCD driving chips to drive OLED is possible and can get better effect.关键词：AMOLED;pixel driving circuit;simulation;gray level;peripheral driving circuitry145|341|2更新时间：2020-08-11
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Transient Dynamics of Excited States in PbS Nanoparticles by Femtosecond Pump and Probe Spectroscopy
摘要：Semiconductor nanoparticles have recently attracted much attention for their potential applications in making photonic devices,which can benefit from the control of the size,spectral tunability,enhancement of the third-order nonlinear optical properties,and the ultrafast relaxation dynamics.PbS-doped glass,recently reported as a saturable absorber for mode locking of a Cr:forsterite laser,is one of the most noteworthy examples of utilization of optical nonlinearities in PbS semiconductor nanoparticles.The study of nonlinear absorption and its dynamic behavior in PbS semiconductor nanoparticles is an important research topic both for the basic research and for its applications.Silicon dioxide films incorporated with lead sulfide semiconductor nanoparticles were synthesized by using the sol-gel method and the dip-coating technique.We have investigated the transient dynamics of PbS nanoparticles by one-color femtosecond pump-probe method at different wavelengths and various excitation densities.The experimental result shows that the absorption saturation of exciton resonance results in photobleaching at 620 nm in low excitation density condition.The decay process of the bleaching includes two components,the fast one from free carriers scattering and the slow one from trapped carriers scattering.The photo-induced absorptions at 753 nm and 800 nm were caused by the biexciton effect.The experimental result indicates that when the excitation and probe wavelength were chosen on the low-energy side of the exciton resonance,it could overlap the ground-state-biexciton transition.At low excitation density(48μJ/cm2),the average number of excited e-h pairs in each nanoparticle was much less than one,and photo-induced absorption of the biexciton effect and photobleaching of the exciton transition were observed simultaneously. As pump density increases,the absorption saturation gradually disappears,and only the photo-induced absorption can be observed at the pump density of 4mJ/cm2,indicating that the biexciton effect is depends strongly on the density of excited carriers and plays a significant role in the multiple e-h pair in PbS nanoparticles.关键词：PbS nanoparticles;femtosecond pump and probe technique;saturable absorption;biexciton effect;relaxation151|91|0更新时间：2020-08-11 - 摘要：The intense blue-white emitting phosphors Ca2SiO3Cl2:Eu2+ were synthesized by traditional high temperature solid state reaction method,and their luminescence properties were studied.The results indicate that the emission band consists of two peaks located at 420 and 498 nm,respectively.The two peaks are(originated) from the transition 5d→4f of Eu2+ ions that occupy the two Ca2+ sites in the crystal of Ca2SiO3Cl2.The emitting of Ca2SiO3Cl2:Eu2+ can be changed from blue-white to green-white color by adjusting the Eu2+ concentration.When the Eu2+ concentration is 0.005 mol-1,the sample presents intense blue-white emitting.The excitation spectra of the two emissions both extend from 250 nm to 410 nm,and their peaks positioned(around) 333 nm and 369 nm,respectively.Ca2SiO3Cl2:Eu2+ is a superior single-phase blue-white phosphor with low-cost and high brightness for white LEDs,Ca2SiO3Cl2:Eu2+ phosphor can be excitated by InGaN chip UV emission effectively.关键词：luminescence;luminescent properties;phosphor;Ca2SiO3Cl2：Eu2+98|113|14更新时间：2020-08-11
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