最新刊期
卷 25 ， 期 4 ， 2004
- 摘要：The electronic structures of copper iodide crystal in γ phase and point defects associated with iodine and copper have been studied with relativistic density functional theory and embedded cluster method(DVM).Through the electronic densities of states of copper iodide crystal and its point defects,the emission and absorption mechanism are studied.The effects of all kinds of point defects on the emission spectrum of copper iodide crystal are also discussed.By the DVM method,(I14Cu16)2+ cluster is used in the simulations of pure copper iodide crystal.In addition,on the basis of(I14Cu16)2+ cluster,other clusters,such as copper vacancies,iodide vacancies,copper interstitial defects and iodide interstitial defects,have been studied as the main forms of its point defects.The excitation energy between different orbits is calculated by the transition state method,regarding the relaxation effect produced by the electronic transition in the crystal.Subsequently the computational result is compared with the experiments and the results by other simulation methods.The results of simulation of the pure copper iodide crystal show that the top of the valence band is consisted of I5p and Cu3d,and the bottom of the conduct band is consisted of Cu4s.The simulation result for the band gap of the pure crystal is 3.1eV,which is in good agreement with the experiment result.The calculation for point defects shows that the defects associated with the tetrahedron interstitial copper formed easier than that of other interstitial atoms in copper iodide crystal.The transition energies between Cu3d and Cu4s in copper tetrahedron interstitial defects are 3.2eV,which is presumed to be related to the broad luminescence bands of CuI crystal.The electronic structure of defects in CuI crystal is firstly calculated by DVM method.By the results,it can give some helpful clues for choosing certain dopants in copper iodide crystal to improve its scintillation charcteristic.And also it is very significative for the growth of super fast CuI sintillator.关键词：CuI crystal;density functional theory;electronic structure;luminescence mechanism125|205|0更新时间：2020-08-11
- 摘要：With the advance in the nanofabrication technology,there has been a great deal of interest in the investigation of quasi-zero-dimensional electronic systems(quantum dots).Because of the wide device applications and a lot of new physical effects in such structures,understanding the electronic properties of these systems is of particular importance.Several studies have already been carried out on the interaction of the electrons with longitudinal-optical(LO) phonons in quantum dots.Recently,Zhu and Kobayashi used the Landau-Pekar variational treatment to study the strong coupling polaron binding energy of the ground state and the average number of virtual phonons around the electron in quantum dots in the presence of magnetic fields.Taking into account the electron-bulk LO-phonon interaction,Kandemir and Altanhan used the Lee-Low-Pines transformation to calculate the polaronic effects for an electron confined in a parabolic quantum dot in a uniform magnetic field.Zhu and Gu investigated the polaronic states in a parabolic quantum dot by using the second order Rayleigh-Schrodinger perturbation theory.It is shown that the absolute values of the ground state energy correction and the excited state energy correction as well as the relevant transition energies increase with decreasing the size of the quantum dot.The results also indicate that the polaron effects in small quantum dots are stronger than those in the corresponding bulk materials.In the papers of Zhou and Gu,by using the variational method of Pekar type,the ground state and the first excited state of the strong coupling magnetopolaron in cylinder-shape and disk-shape quantum dot were considered.The results show that,with the increasing cyclotron frequency and the confinement strength,the magnetopolaron binding energies in both the ground state and the excited state,and the resonance frequency of magnetopolaron are enhanced.However,the properties of magnetopolaron in the excited state in parabolic quantum dot has not been studied so far.In this paper,by using the variational method of Pekar type,both the ground state and the excited state of strong coupling magnetopo-laron in parabolic quantum dot were studied.The magnetopolaron binding energies in both the ground state and the excited state,and the resonance frequency of magnetopolaron were calculated.Their dependence on the cyclotron frequency and the confinement strength was depicted.关键词：parabolic quantum dot;strong coupling;magnetopolaron79|100|0更新时间：2020-08-11
- 摘要：GdB3O6 was synthesized by the solid state reaction at high temperatures.The UV excitation and emission spectra were recorded by a Hitachi M850 fluorescent spectrometer at room temperature.Because the part of 6GJ energy levels of Gd3+ are below 50000cm-1,so these 6GJ energy levels of Gd3+ could be measured by UV excitation.The observation of photon cascade emission of the Gd3+ ion in GdB3O6 under 8S7/2→6GJ ultraviolet excitation(202nm) was reported.In this host lattice,the lowest energy state of the Gd3+ 4f5d excited configuration is located above the 6GJ state.The 6GJ→6PJ and 6GJ→6IJ transitions are responsible for the first photon emission.The second photon emission originates from the 6PJ→8S7/2 transitions.In the GdB3O6 host,the energy difference ΔE between the6D9/2 and 6I11/2(about 2900cm-1),and that between 6I7/2 and 6PJ(about 3900cm-1) are smaller,the multiphonon relaxation rate exceeds remarkably the radiative decay rate,so the absence of emission from the 6DJ and 6IJ states to the ground state 8S7/2 is attributed to the efficient multiphonon 6DJ→6IJ and 6IJ→6PJ relaxation.关键词：photon cascade emission;Gd3+;borate;optical properties101|190|0更新时间：2020-08-11
- 摘要：A kind of up-conversion luminescence material with new composition was prepared,the material not only has the higher up-conversion luminescence efficiency,but also avoids the defect of fluoride host material.It consists of 58.52%PbF2-34.43%GeO2 -3%Al2O3-0.05%Er2O3-4%Yb2O3,among which GeO2 acts as the oxide of glass formation,PbF2and Al2O3 act as the regulator,and co-doped Er3+and Yb3+ ions are taken as the objects of up-conversion investigation.The up-conversion emissive spectra were measured under 980nm excitation using a semiconductor laser diode,the very strong red light of 658nm and green light of 548nm and 526nm can be observed.Moreover,the red light emissive intensity is far stronger than that of the green light one.A nonlinear curve fitting to the relationship between up-conversion emissive intensity and excitation light power was made,it is concluded that both red emission and green emission are the absorption process of double-photon.The relationship between the operation current of 980nm laser diode and up-conversion fluorescence intensity was investigated,and the up-conversion luminescence characteristic was discussed.关键词：up-conversion luminescence;rare earth ions of Er3+and yb3+;fluorin-oxygen glass93|73|7更新时间：2020-08-11
- 摘要：Y2O3:Eu3+ is a red phosphor with good property.It is usually synthesized by high temperature solid state method.The particle size of the phosphor prepared by this method is lager ,so it must be milled when used.The oxalic acid precipitation method was developed to synthesize non-grinded and small-size red phosphor in our experiment.Firstly,the mixture of Y2O3 and Eu2O3 was dissolved in nitric acid in certain proportion.Secondly,the prepared oxalic acid solution was placed in a reactor and at the same time a little surfactant was added in it.When the reaction temperature was controlled to be certain value,the nitric acid solution of Y,Eu was added.Afterwards the precipitation formed and then washed,filtrated,dried and calcined to become white Y2O3:Eu3+ power.The Luminescent properties of the phosphor were mainly studied .The result shows that the particle diameter is 20～30nm.The agglomerate size is D50=0.53μm.The particle is fine and the granularity distribution displays a narrow and normal distribution.The maximum excitation spectrum of the phosphor peaks at λ=252.2nm,red shift 19.2nm compared with micro-Y2O3:Eu3+.The maximum emission spectrum peaks at λ=612nm under 254nm excitation.Compared with the ordinary power of Y2O3:Eu3+ ,the emission spectrum of the phosphor appears unchangeable.The luminescent intensity increases with growing of agglomerate size.The addition of Eu3+ can constitute luminescent centers when Y2O3 as basic particle and Eu3+as activator in Y2O3:Eu3+ .The less the amount of the added Eu3+ is,the lower the luminescent brightness of the phosphor is.The critical concentration of Eu3+ increases from 6% for micro-Y2O3:Eu3+ to 9% for nano-Y2O3:Eu3+.The phosphor shows a relative luminescent brightness about 70% of that of the micro-Y2O3:Eu3+,because of the existence of hanging-bonds and defects on the surface of nano-Y2O3:Eu3+ particles.The phosphor particle was increased and the defects on the surface of the phosphor was decreased at high temperature,so luminescent brightness of the phosphors was increased.Adding assist melting agent can decrease sintering temperature and increase D50 of the phosphor,and the brightness of the phosphor increased,too.Coating-process on phosphor can dispel defact and increase brightness.The luminescent chromatic coordinate parameters of the phosphor are x=0.6479,y=0.3442 ,which accords with the phosphor.关键词：oxalic acid precipitation;small-sized;phosphor;Y2O3:Eu3+;luminescence97|11|2更新时间：2020-08-11
- 摘要：Y2O3:Eu3+ is a red phosphor with good property.It is usually synthesized by high temperature solid state method.The particle size of the phosphor prepared by this method is lager ,so it must be milled when used.The oxalic acid precipitation method was developed to synthesize non-grinded and small-size red phosphor in our experiment.Firstly,the mixture of Y2O3 and Eu2O3 was dissolved in nitric acid in certain proportion.Secondly,the prepared oxalic acid solution was placed in a reactor and at the same time a little surfactant was added in it.When the reaction temperature was controlled to be certain value,the nitric acid solution of Y,Eu was added.Afterwards the precipitation formed and then washed,filtrated,dried and calcined to become white Y2O3:Eu3+ power.The Luminescent properties of the phosphor were mainly studied .The result shows that the particle diameter is 20～30nm.The agglomerate size is D50=0.53μm.The particle is fine and the granularity distribution displays a narrow and normal distribution.The maximum excitation spectrum of the phosphor peaks at λ=252.2nm,red shift 19.2nm compared with micro-Y2O3:Eu3+.The maximum emission spectrum peaks at λ=612nm under 254nm excitation.Compared with the ordinary power of Y2O3:Eu3+ ,the emission spectrum of the phosphor appears unchangeable.The luminescent intensity increases with growing of agglomerate size.The addition of Eu3+ can constitute luminescent centers when Y2O3 as basic particle and Eu3+as activator in Y2O3:Eu3+ .The less the amount of the added Eu3+ is,the lower the luminescent brightness of the phosphor is.The critical concentration of Eu3+ increases from 6% for micro-Y2O3:Eu3+ to 9% for nano-Y2O3:Eu3+.The phosphor shows a relative luminescent brightness about 70% of that of the micro-Y2O3:Eu3+,because of the existence of hanging-bonds and defects on the surface of nano-Y2O3:Eu3+ particles.The phosphor particle was increased and the defects on the surface of the phosphor was decreased at high temperature,so luminescent brightness of the phosphors was increased.Adding assist melting agent can decrease sintering temperature and increase D50 of the phosphor,and the brightness of the phosphor increased,too.Coating-process on phosphor can dispel defact and increase brightness.The luminescent chromatic coordinate parameters of the phosphor are x=0.6479,y=0.3442 ,which accords with the phosphor.关键词：oxalic acid precipitation;small-sized;phosphor;Y2O3：Eu3+;luminescence74|45|2更新时间：2020-08-11
- 摘要：Solid-state blue and green light sources have many important uses.For example they are desirable for high-density optical storage,color displays,optoelectronics and medical diagnostics.Up to now,the conversion from infrared into visible wavelength has attracted much attention and up-conversion material doped with rare earth ions has been intensively studied on various crystals and glasses.Most oxide glasses are much more chemically and mechanically stable and also are more easily fabricated into various shapes,but their larger phonon energy results in the high inefficient rate of infrared up-conversion.As known to all,fluoride material has lower phonon energy,which is very useful for improving the up-conversion efficiency,whereas due to poor chemical stability,disappointing mechanical strength and low laser damage threshold,all these problems limit its development and application.Nowadays,people are trying preparing up-conversion luminescence material of oxy-fluoride.This type of material possesses both the high up-conversion luminescence efficiency of fluoride material and characters of oxide materials.In this paper,the preparation of glass ceramics doped with Yb3+,Er3+ in composition of PbF2+GeO2+WO3+SiO2+NaF and the effect of the rare-earth ions on the host material are reported.The emission spectrum was measured under a 980nm laser diode excitation.It shows a strong up-conversion emission peak at 550nm and weak peaks at 528nm and 650nm.The experimental results were discussed and the up-conversion mechanism was established.The spectroscopic properties,the composition of host glass,the preparation parameter,the concentration of rare-earth ion,the dependence of emission intensity on the excitaion power were also discussed.In our experiment we select PbF2,GeO2,WO3,SiO2 and NaF as host constituents.Pb3+ and W6+ both have larger masses; moreover the mass of F- is bigger than that of O2-.So the host glass bears good transmittance in the near infrared region.Because of smaller bond strength of Ge—O,GeO2 hardly absorbs near infrared light.Heavy metal fluorides with low phonon energy easily produce transfer course of free radiation.GeO2 and SiO2 are both glass formers among the components and useful to generate glass in network structures.Through many experiments we set the annealing temperature at 380℃ and the melting temperature at 950℃.The optimum proportion is of c(Yb3+):c(Er3+)= 5:1.关键词：up-conversion luminescence;rare-earth ion;glass ceramics116|59|0更新时间：2020-08-11
- 摘要：In recent years,the experimental advance has stimulated interest in semiconductor quantum wells and heterojunctions to explore the novel phenomena and their applications.Some authors investigated the shallow donors in quantum well with presence of a magnetic field.But few studies focused on the states of impurities near the heterojunction interface with the external magnetic field,especially in consideration of the electronic screening effect.A variational method is adopted to investigate the binding energies of shallow donor impurities near the interface of a single semiconductor heterojunction system in the presence of a static uniform magnetic field by considering a triangular potential to approximate the interface potential.The electronic image potential and the screened Coulombic impurity potential are also taken into account to investigate the impurity state binding energy.Numerical computation has been performed for the GaAs/AlxGa1-xAs structure.For a given impurity position the binding energy as a function of magnetic field,perpendicular to the interface,shows a monotonic increase tendency with increasing the magnetic field strength B,which makes the electronic wave functions highly localized to magnify the effective Coulombic attraction.This monotonic property is different from the maximum property obtained by Hollox.The binding energy is also computed as a function of the impurity position z0 to show that the binding energy increases at first,and then decreases with increasing the distance between the impurity and the interface.The results corresponding to with and without the screening effect are compared.It is found that even in the presence of a magnetic field the screening effect dramatically decreases the impurity state binding energy,which is obviously influenced by the barrier potential and the conduction band bending.The binding energy is sensitive to the areal electron density.It is also found that the influence of the electron image potential is negligibly small so that it needs to be considered in the further discussion.This is consistent with the early conclusion for without a magnetic field case.关键词：heterojunction;magnetic field;impurity state;screening effect76|62|2更新时间：2020-08-11
- 摘要：The Si-doping AlGaInP/GaInP multiple quantum wells red LED wafers were grown by EMCORE GS/3200 low pressure metalorganic chemical vapor deposition(MOCVD).Properties of these wafers were investigated by double crystal X-ray diffraction and photoluminescence measurement.The influence of Si-doping on the characteristics of AlGaInP/GaInP multiple quantum wells was studied.The GaAs substrates used were cut 15 degree off the(100) plane towards the [011] direction.TMGa,TMIn,TMAl,AsH3,and PH3 were used as Ga,In,Al,As,P precursors,respectively.CP2Mg and SiH4 were used as p and n type doping reagents.The growth temperature was 620～72℃.The sequence of layers grown on n-GaAs substrate was,0.5μm n-GaAs buffer with the carrier concentration of about 5×1017cm-3,15 periods Al0.5Ga0.5As:Si/AlAs:Si DBR,0.5μm n-(Al0.7Ga0.3)0.5In0.5P cladding layer with carrier concentration of about 3×1017cm-3,(Al0.3Ga0.7)0.5In0.5P/Ga0.5In0.5P multiple quantum wells,0.5μm p-(Al0.7Ga0.3)0.5In0.5P cladding layer with carrier concentration of about 6×1017cm-3,and 5μm p-GaP current spreading layer with carrier concentration of about 5×1018cm-3.Three AlGaInP LED wafers with different Si doping in 10 periods MQW were studied.The Sample A is unintentional doping 10 periods MQW wafer.The Sample B is Si-doping in the barriers wafer.The Sample C was Sidoping in the barriers and wells wafer.The doping dose was the same as that of the 0.5μm n-(Al0.7Ga0.3)0.5In0.5P cladding layer.The(004) X-ray diffraction curves of these three wafers with different Si doping in 10 periods MQW were obtained.Besides the peaks of GaAs and AlGaInP,two satellite peaks are observed in all samples,which are listed by dashed line.It indicates that the interface quality of MQW does not become worse by Si doping.The periods of Sample A,B and C is 14.6,15.2,15.7nm,respectively.The growth rate of MQW increases with the Si-doping.In PL spectra of these three samples at room temperature,the peak intensity of Sample B is strong as 13 times as that of Sample A,and the peak intensity of Sample C is strong as 28 times as that of Sample A.It indicates that the PL intensity of MQW can be largely enhanced by the Si doping in MQW.Moreover,the peak position and width do not obviously change by Si-doping.关键词：AlGaInP;AlGaInP/GaInP MQW;double crystal X-ray diffraction;Si-doping;photoluminescence86|98|0更新时间：2020-08-11
- 摘要：In the case of no determination of Al composition and p-doping density in MOCVD epitaxy of AlGaInP double heterostructure light emitting diodes,the relation of Al composition and luminescent efficiency is gotten under various p-doping density by analyzing carrier transportion in double heterojunction of LED,and the principle of doping density and Al composition vs.luminescent efficiency can be derived.So this conclusion would have a guide to device design and MOCVD epitaxy.关键词：AlGaInP;Al composition;p-doping;luminescent efficiency119|85|0更新时间：2020-08-11
- 摘要：Recently much attention has been paid to short wavelength lasers for use in high density information storage.It is widely accepted that ZnO is one of the most promising materials for producing an ultraviolet laser at room temperature due to its wide direct band gap(Eg=3.37eV) and large excitonic binding energy of 60meV.It has potential uses in optoelectronical systems such as light emitting diodes(LEDs),photodetectors,electroluminecence devices and solar cells.To obtain high quality ZnO thin films a variety of techniques may be used such as molecular beam epitaxy(MBE),metal organic chemical vapor deposition(MOCVD),magnetron sputtering,pulsed laser deposition,and so on.Among them,MOCVD provides the advantage of growing high-quality films due to its versatility in controlling the various thermodynamic interactions.ZnO has not only the same crystal structure as GaN,but also a larger exciton binding energy of 60meV,which is 2.4 times that of GaN.This indicates that ZnO should be the most potential material to realize the next generation UV semiconductor laser.High quality ZnO films were deposited on c-Al2O3 substrate by the plasma-assisted metal-organic chemical vapor deposition.Strong optically pumped ultraviolet(UV) emission was observed.PL spectra under different excitation powers were performed.The PL intensity as a function of the excitation power,it is obvious that the PL intensity is linearly dependent on the excitation power.This indicates that the dominant photoluminescence of the sample should be the excitonic radiative recombination at room temperature.Optically pumped UV lasing spectrum of ZnO film was observed.The samples were optically pumped by a frequency-tripled mode-locked Nd:YAG laser 355nm emission,with 10 Hz repetition rate,and 15 ps pulse width.The pump beam was focused to a spot with diameter of about 25μm on the surface of ZnO film.The threshold of lasing was as low as 0.28 μJ.From the lasing spectrum,we could find that the lasing peak has much narrow line-width less than 0.03nm.In this paper,high quality ZnO films were grown on c-Al2O3 by MOCVD.Optimized growth condition was obtained by XRD and PL measurements.ZnO films were strongly c-oriented from XRD measurement.Optically pumped UV lasing was observed in all kinds of directions at room temperature.This was due to the self-formed resonance cavities.关键词：MOCVD method;ZnO film;optically pumped UV lasing74|69|1更新时间：2020-08-11
- 摘要：ZnO films were grown on sapphire substrate(0001) plane by atmospheric MOCVD.Surface mor-phology,crystalline quality,PL and electrical properties of the films were studied using AFM,DXRD,RBS/C,photolumi-nescence and Hall measurements.A columnar structure with an average column size of 1.89μm in diameter and a RMS of 6.257nm of the sample was observed by AFM measurement.The sample shows strong near-band edge emission at 380nm in PL spectra at room temperature,FWHM of the peak is 15nm,no deep level emission was observed.The electrical properties of the samples were measured by Hall measurements at room temperature.The carrier concentration and mobility are 2×1017cm-3and 75cm2·V-1·s-1,respectively.Double-crystal X-ray diffraction and Rutherford backscattering/channel(RBS/C)analysis were used to check the crystalline quality of the film,FWHM of the DXRD rocking curve(omega-scan) is 0.04,and the RBS/C minimum yield χmin of the film is 3.1%.Both these results indicate that the ZnO film has a good crystalline quality.关键词：MOCVD;ZnO;AFM;PL;DXRD;RBS/C112|62|0更新时间：2020-08-11
- 摘要：Photoluminescence mechanism of porous silicon has been studied and discussed for many years,a lot of academic models to explain this phenomenon were proposed.Each model can interpret certain experimental results,but can’t explain others or even can be contradictious,so it is debated and studied to date.The substrates used in this work were all ptype Si wafer with resistivity between 8～13Ω·cm and(111) crystalline orientation.The samples were prepared by anodic etching method in doublecell.The anodic etching was carried out in a solution of HF and ethanol at constant current density and at room temperature.Specimens were prepared under different conditions of current density,solution concentration and erosion time.Photoluminescence spectra of the samples have mostly four peaks:Peak 1:(660±5)nm;Peak 2:(690±10)nm;Peak 3:(740±5)nm and Peak 4:(775±5)nm.Energy positions corresponding to peak wavelength are:(1.88±0.02)eV;(1.796±0.03)eV;(1.675±0.01)eV and(1.599±0.01)eV respectively.The energy range is 1.6～1.9eV.Relation between preparation conditions and peak wavelength and intensity is set out.The peak wavelength shifts in a little range,but the intensity changes greatly with the difference of preparation conditions,so whole peak position shifts and full width at half maximum changes obviously.Relation between aging time and peak wavelength and intensity is set out also.With aging time,three main peak position changes less,some shift to the blue and some are almost immobile and others shift to the red,but the peak intensity weaken more and more.Different preparation conditions can generate different microcosmic structure,porous silicon with different structure perhaps has more different optical properties and photoluminescence properties.Structure and photo-luminescence properties of prepared porous silicon can change with the process of preservation.Experimental results suggest that photoluminescence of porous silicon is a result of multiple photoluminescence mechanism operating together; size distribution in a certain range not only influence on the bandwidth,but also is one of reasons inducing multipeak phenomenon.Structure characteristics of porous silicon determine its photoluminescence properties.关键词：porous silicon;multi-peak emission;photoluminescence mechanism;size distribution96|86|2更新时间：2020-08-11
- 摘要：An analytical model to calculate the electroluminescence(EL) profile at high electric field in single layer structure,taking into account the charge injection process at each electrode,fission and recombination of polaron-excitons in disordered system,is presented.The influences of the barriers of metal/organic interface on EL efficiency are thoroughly studied.When the barrier exceeds about 0.3eV,the EL efficiency will become very small.While lowering the barrier of metal/organic interface,the EL efficiency will be enhanced.With increasing applied voltages,the injection efficiency increases while the recombination efficiency decreases,and when the electric field increases to a critical value,the EL efficiency reaches the maximum and then decreases.It indicates that the EL efficiency is dominated by injection at lower voltages and recombination at higher voltages.It is found this model can reasonably eluci-dates the influence of injection and recombination processes on EL efficiency,which provides a theory to improve the EL efficiency,to optimize the structure and to select suitable electroluminescent materials.关键词：OLED;metal/organic interface;barrier height;EL efficiency93|87|0更新时间：2020-08-11
- 摘要：The red organic LEDs with high brightness and good color purity are necessary for the achievement of full-color emission displays.Commonly,the red OLEDs were made by doping the DCJTB into the Alq3 host due to its stability and charge-transporting ability.But this doped system showed a contrary phenomenon of low efficiency(at high concentrations of DCJTB) or poor color purity(at low concentrations of DCJTB).Meanwhile,the efficiency of these devices declined rapidly after it reached the maximum efficiency point with the applied voltage increasing.Although intensive research has been made in recent years,the performance of red devices is not satisfactory either the luminance efficiencies or the color purity.In this paper,we fabricated organic EL devices with double emitting zone in order to obtain the efficiency independent on the applied vol-tage and together with good color purity.The saturated red organic light-emitting diode(OLED) has been realized by doping an emitting material in the hole-transporting layer(HTL)and electron-transporting layer(ETL) to form double emitting zone.The red dopant,DCJTB,was doped into the NPB layer and Alq3 layer,which both act as the emitting layer.The optimal device,with a structure of ITO/CuPc/NPB/NPB:DCJTB/Alq3:DCJTB/Alq3/LiF/Al,showed a good performance of the current efficiency being relatively independent of the drive voltage in a wide range from 8V to 20V(only reduced by 4%)and the chromaticity coordinates changed from 8V(x=0.6287,y=0.3663)to 20V(x=0.6075,y=0.3841),and the devices maintain a pure red emission.That may be helpful to ameliorate the lifetime of the organic electroluminescence(EL) devices and adjust the gray-scale for the future full-color display panel.关键词：OEL;luminance efficiency;chromaticity coordinates;doping in double emitting layer85|84|1更新时间：2020-08-11
- 摘要：Since the first reports of efficient electroluminescence from an organic thin film device using the metal chelate tris(8-hydroxyquinoline)aluminum(Alq3) as the emissive layer materials,some efforts have been devoted not only to tailor emission wavelength by a functional group introduced onto the quinolinolato ligand,but also to synthesize the new metal chelating compound.However,there is no report on the relationship between the substituent of phenyl moiety in the 2-position of 8-quinolinol and an emission property.Therefore,a systematic study to clarify a relationship between a molecular structure and emission property is evidently necessary for developing a more useful emissive compound.Bis(2-phenyl-8-hydroxyquinolato)zinc and bis(8-hydroxyquinolato)zinc were synthesized firstly according to the relating reference.The melting point,composition and structure were also determined by a series test methods.The substituent of phenyl group dependence of luminescence band of the 8-quinolinolato anions was systematically investigated with excitation spectra and emission spectra of prepared samples.The luminescence band at 495nm for bis(8-hydroxyquinolato)zinc is presented under 225,283,348,395nm excitations,respectively.The luminescence band at 521nm for bis(2-phenyl-8-hydroxyquinolato)zinc is presented under 225,283,348,395,465nm excitation,respectively,which showed to exhibit strong photoluminescence efficiency.It is suggested that the assignment of absorption bands at 225,283,348nm of the above mentioned two samples could be ascribed to the β,ρ and α band of π→π* transition in the quinolinolato ring.The absorption bands at 395nm existing in the above mentioned two samples have been probably attributed to the charge transfer between the d orbital on zinc ion and vacant π orbital on the ligand.The new absorption band of 465nm presented in bis(2-phenyl-8-hydroxyquinolato)zinc chelate is a new energy level ascribed to the intramolecular charge transfer between the different conjugating π systems existed in the quinolinolato ring and in the substituent of phenyl moiety in the 2-position of 8-quinolinol,which also means that this new chelate exhibits photostimulated luminescence not only with ultraviolet radiation,but also visible light at room temperature.It is suggested that introducing the substituent of phenyl moiety in the 2-position of 8-quinolinol is an effective way for red shifted emission,which changes the energy level of the highest occupied molecular orbital(HOMO) through π orbital interactions.Further,insight into the detailed mechanism of photostimulated luminescence from bis(2-phenyl-8-hydroxyquinolato)zinc chelate requires additional experimental and theoretical studies.Industrially the photostimulated luminescence phenomenon of the detailed mechanism of photostimulated luminescence from bis(2-phenyl-8-hydroxyquinolato)zinc could have use as a new type fluorescent material for optical memories and organic light emission devices.关键词：bis(2-phenyl-8-hydroxyquinolato)zinc;bis(8-hydroxyquinolato)zinc;fluorescent property;red shift84|47|6更新时间：2020-08-11
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Synthesis, Characterization and Photoluminescent Property of Lithium Complex with 8-Hydroxyquinoline
摘要：Blue electroluminescent emitter is essential for the development of a full-color display.However,blue emitting organic materials are rare compared to those of green.Lithium complex with 8-hydroxyquinoline with high yield and purity,which is a blue emitter,was synthesized by liquid-phase reaction and characterized by FTIR spectra,UV absorption spectra,XRD spectra,fluorescence spectra and its structure of energy band was studied by UV absorption spectra,cyclic voltammetry and fluorescence spectra.Results show that pH value and solvent have high influence on yield of Liq.From IR spectra of Liq,the broad characteristic peak at 3180cm-1 corresponding to OH- stretching vibration peak(νOH)and OH-bending vibration peak at 1223cm-1disappear in complex,the new peak appear at 483cm-1,520cm-1 ,which correspond to Li-Obond,which is ion bond.Liq is a thermally stable material,whose melting point is 365℃,which can form easily high quality amorphous film at glass substrates cleaned by vacuum evaporation.The powder of Liq is crystallographic,having two intense diffraction peak at 18.8°,21.7° in XRD spectra,whereas its film is amorphous.In the absorption spectra of Liq film,there are two absorption peak at 259nm,which is strong,and at 363nm,which is weak.The long wave absorption peak,which has contribution to fluorescence,was attributed to charge transfer transition from phenoxide ring with oxide to pyridyl ring with nitrogen.The strength of metal-nitrogen bond affects the position of this peak,the weaker metal-nitrogen bond,the shorter absorption wavelength.The LUMO energy,HOMO energy and optical gap of Liq is 2.90,5.91,3.01eV,respectively.Liq film can emit intense blue fluorescence with peak wavelength at 452nm and a full width at half-maximum of 69.4nm under UV excitation at 363nm.The Stokes shift of Liq film is about 5424cm-1 because of electron-phonon interaction and the trapping state in band gap.关键词：(8-quinolinolato)lithium;synthesis;characterization;photoluminescent property147|150|6更新时间：2020-08-11 - 摘要：To investigate the feasibility of non-traumatic detection of porphyrin for cancer diagnosis,optical property of human skin was studied by spectral analysis.The reflexion,transmission and fluorescence spectra of skin were taken using RF-5301PC spectrophotometer.The spectra suggest that,in the skin,there were mainly four kinds of illuminant substances——protein,carotenoid,NADH and melanin.The excitation and emission spectra of skin were taken to verify what affect of those illuminant substances might cause in porphyrin detection.The fluorescence at 360nm from the skin with excitation wavelength of 280nm was determined to be the result from protein.And at 350nm excitation,an emission spectrum around 452nm,similar to that from carotenoid sample,was observed.The observed fluorescence at 400nm and 460nm might result from the protein and NADH in the skin respectively.It was known from the literature that melanin had no emission at observed range,while oxidized melanin had fluorescence at 580nm,which was also observed from the fluore-scence spectra of the skin.No emissions,from those illuminant substances in the skin,were observed at the fluorescence wavelength of porphirin,625～630nm.It demonstrates that the illuminant substance of skin won’t affect the measurement of porphyrin.It was also clear,from the transmission spectra of skin,that the transmission window of skin is from 600nm to 900nm,which confirms the possibility of the non-traumatic detection of porphyrin.关键词：non-traumatic;skin;porphyrin;protein;carotenoid;melanin;spectral analysis154|97|0更新时间：2020-08-11
- 摘要：Eugenol is main chemical component of flos caryophylli dry bud from eugenia caryophyllata thunb.It has several biological roles,including sterilization function,antioxidation and narcotism.It has been widely used in food and medicine.The detection of eugenol is of considerable interests for food and pharmaceutical analysis.To date,a number of methods such as gas chromatography,gas chromatography/mass spectrometry,high-performance liquid chromatography,thin layer chromatography and spectrophotometry has been reported.However,former four methods required expensive instrumentation and tedious sample pretreatment and last method suffered from lower sensitivity.Therefore,it is necessary to explore new sensitive and simple method for the determination of eugenol.In this work,it was found that eugenol inhibited strongly the chemiluminescence of luminol-DMSO-NaOH system.On this basis,a novel flow injection method with inhibited chemiluminescent detection was developed.The optimal conditions for the detection of eugenol are as follows:6.0×10-4 mol/L pH 8.00 luminol,0.5 mol/L DMSO,0.1 mol/L NaOH.The method is sensitive,fast,and simple,superior to all documented methods.It allows for the detection of eugenol in the range of 5×10-9～1×10-6 g/mL with a detection limit of 2.97×10-9g/mL.The relative standard deviation is 1.63% for the determination of 5×10-7g/mL eugenol(n=11).The method has been successfully used to determine eugenol in traditional Chinese medicine ding erqi tie with the recoveries of 93.3%98.3% and the results obtained by this method were comparable with that by gas chromatography.Finally,the CL spectra and UV-visible absorption spectra were studied and the CL inhibition mechanism has been proposed due to the competition of eugenol with luminol for O2·- generated by DMSO-NaOH-O2 system.关键词：eugenol;luminol;DMSO;chemiluminescence inhibition113|99|6更新时间：2020-08-11
- 摘要：The UV/visible absorption spectra of LiNbO3,Fe:LiNbO3,and Zn:Fe:LiNbO3 crystals grown by Bridgman method were measured and investigated.The characteristics of the absorption were explained,and the effects of growth processing on the absorption spectra were also discussed.The results indicate that the absorption edge of lithium niobate shifts to longer wavelength,and the absorption intensity in the range of 350450nm band increases along the direction of crystal growth.The reason of above causes is lacking of lithium composition in crystal,which resulted from the volatilization and segregation of lithium in growth period.A band at 480nm which attributed to Fe2+ ion absorption was observed in Fe:LiNbO3 crystal,and it was found that the intensity of the band increases along the growth direction,which means the increase of Fe2+ ion along the direction,and the incorporation of Fe in LiNbO3 resulted in a red shift of absorption edge.However,the concentration of Fe2+ ion in the obtained crystal increases obviously compared with that of Fe:LiNbO3 in same quantity of Fe dopant,which was quite different from that of crystal grown by the Czochralski method.When ZnO in w(ZnO)=1.7% was doped,a blue shift of absorption edge was observed,but a slightly red shift for w(ZnO)=3.4% ZnO.Among Fe-doped and Zn/Fe co-doped LiNbO3 crystals,1.7% ZnO doped Fe:LiNbO3 has biggest change of Fe2+ ion mass fraction from bottom to top part of crystal.A stronger suppressing effect on Fe2+ concentration in Zn:Fe:LiNbO3 single crystals resulted from doping w(ZnO)=1.7% than w(ZnO)=3.4%.The effect of the special growth technology on the Fe2+ concentration was analyzed and discussed.关键词：lithium niobate crystals;absorption spectra;Bridgman method113|9|1更新时间：2020-08-11
- 摘要：The UV/visible absorption spectra of LiNbO3,Fe:LiNbO3,and Zn:Fe:LiNbO3 crystals grown by Bridgman method were measured and investigated.The characteristics of the absorption were explained,and the effects of growth processing on the absorption spectra were also discussed.The results indicate that the absorption edge of lithium niobate shifts to longer wavelength,and the absorption intensity in the range of 350450nm band increases along the direction of crystal growth.The reason of above causes is lacking of lithium composition in crystal,which resulted from the volatilization and segregation of lithium in growth period.A band at 480nm which attributed to Fe2+ ion absorption was observed in Fe:LiNbO3 crystal,and it was found that the intensity of the band increases along the growth direction,which means the increase of Fe2+ ion along the direction,and the incorporation of Fe in LiNbO3 resulted in a red shift of absorption edge.However,the concentration of Fe2+ ion in the obtained crystal increases obviously compared with that of Fe:LiNbO3 in same quantity of Fe dopant,which was quite different from that of crystal grown by the Czochralski method.When ZnO in w(ZnO)=1.7% was doped,a blue shift of absorption edge was observed,but a slightly red shift for w(ZnO)=3.4% ZnO.Among Fe-doped and Zn/Fe co-doped LiNbO3 crystals,1.7% ZnO doped Fe:LiNbO3 has biggest change of Fe2+ ion mass fraction from bottom to top part of crystal.A stronger suppressing effect on Fe2+ concentration in Zn:Fe:LiNbO3 single crystals resulted from doping w(ZnO)=1.7% than w(ZnO)=3.4%.The effect of the special growth technology on the Fe2+ concentration was analyzed and discussed.关键词：lithium niobate crystals;absorption spectra;Bridgman method78|69|1更新时间：2020-08-11
- 摘要：Zn2SiO4:Mn is well-known as green emitting phosphor in PDPs.Zn2SiO4:Mn is also widely used in cathode ray tube(CRT),tri-color lamps,color television and thin film electroluminescence devices.Powder samples of Zn2SiO4:Mn is usually prepared by solid state reaction.Recently,Zn2SiO4:Mn phosphors are also synthesized by sol-gel,hydrothermal,spry pyrolysis method,etc..In recent years,more and more attention is paid to combustion synthesis(also called self-propagation high-temperature synthesis) because of its advantages,such as production highly crystalline powders in the as-synthesized state,having higher surface areas,and more homogeneous etc.Zn2SiO4:Mn(0≤x≤0.10) powder samples were synthesized successfully by solution combustion process,and its photoluminescence was also investigated.The single-phase of Zn2-xSiO4:xMn(0≤x≤0.10,Willemite) was obtained by combustion synthesis at as low as 600℃ for few minutes,then by heat treatment at above 900℃ for 4h.In the excitation spectra of Zn2-xSiO4:xMn(0<x≤0.10),the strong broad excitation band at about 254nm is due to 6A1→4T1 transition of Mn2+ with monitoring at 525nm emission.At about 525nm,the intense broad band emission was observed under 254nm excitation in Zn2-xSiO4:xMn(0<x≤0.10).This broad band is attributed to 4T1→6A1 transition of Mn2+.SEM photography shows its spherical morphology.The results indicated that luminescence efficiency,the location of the strongest band and the optimum concentration of activator depend on starting materials,combustion temperatures,the dosage of fuels and the size of powder samples etc.关键词：Zn2SiO4:Mn;combustion technique;phosphors95|12|5更新时间：2020-08-11
- 摘要：Zn2SiO4:Mn is well-known as green emitting phosphor in PDPs.Zn2SiO4:Mn is also widely used in cathode ray tube(CRT),tri-color lamps,color television and thin film electroluminescence devices.Powder samples of Zn2SiO4:Mn is usually prepared by solid state reaction.Recently,Zn2SiO4:Mn phosphors are also synthesized by sol-gel,hydrothermal,spry pyrolysis method,etc..In recent years,more and more attention is paid to combustion synthesis(also called self-propagation high-temperature synthesis) because of its advantages,such as production highly crystalline powders in the as-synthesized state,having higher surface areas,and more homogeneous etc.Zn2SiO4:Mn(0≤x≤0.10) powder samples were synthesized successfully by solution combustion process,and its photoluminescence was also investigated.The single-phase of Zn2-xSiO4:xMn(0≤x≤0.10,Willemite) was obtained by combustion synthesis at as low as 600℃ for few minutes,then by heat treatment at above 900℃ for 4h.In the excitation spectra of Zn2-xSiO4:xMn(0<x≤0.10),the strong broad excitation band at about 254nm is due to 6A1→4T1 transition of Mn2+ with monitoring at 525nm emission.At about 525nm,the intense broad band emission was observed under 254nm excitation in Zn2-xSiO4:xMn(0<x≤0.10).This broad band is attributed to 4T1→6A1 transition of Mn2+.SEM photography shows its spherical morphology.The results indicated that luminescence efficiency,the location of the strongest band and the optimum concentration of activator depend on starting materials,combustion temperatures,the dosage of fuels and the size of powder samples etc.关键词：Zn2SiO4：Mn;combustion technique;phosphors87|54|5更新时间：2020-08-11
- 摘要：Carbon-nanotube(CNT) is well fitted to field emission for its geometry.A very high electric field can be gotten near its apex.Some of advantages,such as low turn of voltage and stable field emission,made CNTs as an ideal field emission material.The field enhancement factor is an important parameter which effects on the emission current obviously.Soluting the Laplace function is needed,however the special geometry made this solution difficult.Finite element method is a good choice with the increase ment of speed and memory of computer.A commercial code ANSYS was used to analyze the field enhancement factor of CNTs.A single CNT model is extracted from the whole array and some suitable boundary conditions are applied to the model.In order to increase the speed of solution,1/4 part of single CNT model is used in fact.The more accurate results can be got by refining the meshes near apex.The distribution of electric field near the apex of single CNT was analyzed finally.To make the whole process easy and learn better the electric field’s dependence on aspect ratio,an ANSYS parametric design language(APDL),by which great efficient can also be gained,was used.The results are well fitted by the other papers,which testified the whole process:model,mesh and computation.Those methods are good choice to things like this.关键词：CNT;electric field;aspect ratio;electric field enhancement factor90|73|3更新时间：2020-08-11
- 摘要：Alkaline earth sulfides(AES) are excellent and versatile phosphor hosts,hold promise use for many fields.However,these phosphors are easy to hydrolysis in humidity air,and they are easy to dissociate and degrade under high-energy charge,which limit their applications.All of these problems can be solved by using appropriate protective coatings on the surface of phosphor to prevent from the reacting with the atmosphere around the phosphors.Chemical vapor deposition(CVD) method was used extensively,but this CVD process requires elaborate instrumentation,the cost is expensive.A simply wet method was firstly used to coat the unstable AES based phosphor in this paper.The phosphor was added into precursors solution of oxides(usually their soluble salts solution),and then their hydroxides were precipitated on the surface of phosphors through changing the value of pH.The coated phosphors were separated from the liquor resulting and dried at sufficiently high temperature(300～500℃)for a sufficient time(1～2h) to remove water.During this process,part hydrolysis of the surface plays an important role,which make the oxide coating particles adhered better on the phosphor surface.A layer of oxide coating(such as Al2O3,SiO2,MgO,ZnO)was covered on the surface of alkaline earth sulfides based phosphor Ca0.8Sr0.2S:Eu2+,Tm3+ in aqueous medium.XRD,SEM and EDS were used to characterize the coating and the ideal model of coated phosphor and bonding between oxide coating particles and the surface of phosphor were discussed.The stability and optical properties of coated or uncoated phosphor were measured at room temperature.The results indicate that a layer of much smaller oxide coating particles indeed covered on the surface of phosphor,and the stability of coated phosphor has been enhanced to great extent; but oxide coating has no remarkable effects on their emission spectra except a little decrease of their PL intensities within the permitted range.Encapsulated with a layer of oxide coating is a good method to enhance the stability of alkaline earth sulfide based phosphor,and our method is simply and easy to carry out.关键词：alkaline earth sulfide;phosphor;stability;oxide coating106|92|11更新时间：2020-08-11
- 摘要：Liquid crystal displays(LCD’s) are widely used in military electronic systems,equipment,and other devices.In such application,cold cathode fluorescent lamps(CCFLs) are commonly used to provide backlight illumination for the transmissive LC cell.For the cockpit display,a high brightness is required to sunlight readability,and on the other hand,a faint light is necessary in the gloomy sky,even the night sky without any ambient light.So that,a multi-tube CCFL backlight,which with up to 4 tubes of CCFL paralleling each other,is usually rugged in the backlight module.On the other hand,the module must be able to dim the CCFLs for the LCD to display faintly in dark sky.So a proper circuit should be provided for lamps-intensity control from zero to full brightness with no hysteresis or pop on.Even now that the CCFL’s brightness is expressed in a ratio of an input current passing through the tube,but it’s difficult for the current-based intensity-control to dim synchronously the CCFLs in low brightness without the tubes crushing out in succession.Furthermore,even if a single tube,for example a snake type tube,is applied,a phenomenon so-called “thermometer effect” will cause a non-uniformity illuminance too.The current-based intensity-control is not fitted in with this multi-tube backlight module.From the electrical point of view,due to the complicated feature of the CCFL in its impedance,for example,the lamp impedance increases almost inversely with the lamp current,it is very difficult to dim the lamp,especially to provide a very wide luminance adjustment range to about 100% down to 0.1% even to 0.05%.The feature of great range for dimming may make the LCD to meet the special requirement for military.In the case of synchronous driving and if designed excellently,the inverter circuitry with pulse width modulating(PWM) may dim the CCFL very well and is great fit for the dimming of the backlight with multi-tube lamps.Beyond that,the relatioship of the CCFL luminance and the PWM duty is linearity and does not cause excessive lamp decay,thereby the LCD may have a high expected reliability which is a very important specification for military electronic equipment.The feature of CCFLs driven by a power supply circuit based on Royer oscillator,which can invert the DC to AC voltage with about 40kHz in frequency and bring low voltage to high voltage about 600～1200V,is researched in detail.The dynamic response and life relative to PWM-based intensity-control circuit is analyzed experimentally.The experimental data indicate that the reansient response of control circuit is a very important factor for wide dimming range.Especially,the responding time for the power ON or OFF must be minished as small as possible.关键词：CCFL;PWM;brightness modulation;lifetime87|60|2更新时间：2020-08-11
- 摘要：N-doped ZnO thin films are grown by plasma-assisted molecular beam epitaxy(P-MBE) on c-plane sapphire(α-Al2O3) using NO as oxygen source and nitrogen dopant.The gas sources were activated by an oxford Applied Research r.f.(13.56 MHz) plasma source with power of 300 W,A Knudsen effusion cell is used to evaporate elemental zinc with 99.9999% purity.During growth,Zn beam pressure was fixed at 4×10-4 Pa in the growth chamber and growth temperature kept at 300℃.The crystalline quality of ZnO films is characterized by X-ray diffraction,XRD results show that ZnO:N thin films have wurtzite(002) preferred orientation and the full width at half maximum(FWHM) of p-type ZnO films is broaden clearly comparing with that of undoped ZnO thin films.Optical properties of ZnO:N thin films were observed by UV absorption spectra.In absorption spectra,the subbandgap formed by N doping in the ZnO band gap.Electrical properties were measured by four-probeVan der Pauw method.Hall effect measurement shows that the grown samples are p-type ZnO with carrier concentration of 1.20×1019cm-3 ,mobility of 0.0535cm2·V-1·s-1 and resistivity of 9.50 Ω·cm.关键词：ZnO thin film;p-type doping;NO;r.f.plasma;molecular beam epitaxy91|86|3更新时间：2020-08-11
- 摘要：Nanoscale semiconductor structures such as quantum wells,wires,and dots have stimulated great interest due to the predicted improvement in device performance.Many unique and fascinating properties have been demonstrated in semiconductor nanostructures.ZnO is a wide direct band gapⅡ-Ⅵ semiconductor material with a large exciton binding energy of 60meV at room temperature,more larger than the ionization energy at room temperature(26meV),so ZnO is a suitable high efficient ultraviolet material,blue light emitters and detectors at room temperature even at higher temperature.ZnO quantum dots has unique photoelectric properties compared with the bulk material,especial used in UV laser devices filed related with its exciton characteristic.In theory,the larger of exciton bind energy at room temperature,the more easily to realize high efficient stimulated emission at room temperature.So three-dimensional confined nannocrystalline ZnO(or ZnO quan-tum dots) become the hope of high efficient quantum dots laser even nanolaser,and attract great deal of interests of scientists.Therefore,it is very important to study the ground state energy(binding energy) of exciton of ZnO quantum dots in theory.Recent years,many methods were used to prepare quantum dots material with different shape and size,some modern measure technology and instruments were utilized to study the properties of the quantum dots.Many theoretical models were used to research the quantum dots,for example,effective mass qpproximately(EMA),tight binding approximately(TBA),pseudo method(PM),et al.The EMA method is a direct and most useful method for parabola energy band structure.In this paper,we calculate the ground state energy of exciton in ZnO quantum dots by variation method.The calculation is based on a new trial wave function under the effective mass approximation(EMA).The calculation is very simple for the simple trial wave function.Comparision of the calculation results with the experiment values indicates the new trial wave function is right.We also compared the calculation results with the Y.Kayanuma's calculation results.The compared results illuminate the two calculation results is very approach,that make out the new trial wave function is simple and effective,and can applied to other semiconductor quantum dots.关键词：exciton;ZnO;variation method;ground state energy87|75|0更新时间：2020-08-11
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