最新刊期
卷 25 ， 期 5 ， 2004
- 摘要：The behaviours of the charged particles moved in a crystal channel have been controlled by the interaction potential between a charged particles and the crystal.Usual interaction potential is Lindhard potential,Moliere potential and Sine-square potential.The interaction potential between a electron and a crystal may be described by ch-2x potential if particle moved in the channel with the lower index.In the frame of quantum mechanics,Schrodinger equation has been deduced to the hypergeometric equation by this potential.The eigenvalue and the eigefunction problem of the system have been transformed to the eigenvalue and the eigefunction problem of the hypergeometric equation.The relativistic effect and Doppler effect are considered.The eigenvalue and the eigefunction have been calculated,the level distribution and the spectral distribution are induced.As example,the planar channeling radiation of a electron in channel of Si(110) is considered,if the parameters related to particle and the crystal have been chosen.If chosing the distance α=0.096 nm between the crystal surfase,the deep of the potential well V0=27 eV,the electron energy E=5.0 GeV,transition between nearby level has been calculated,and the radiation energy ΔE=49.1 MeV has been obtained.It shows that conformity between the theory and the experiment is better.关键词：Schrodinger equation;hypergeometric fuanction;channelling radiation;eigenvalue;eigenfunction88|66|1更新时间：2020-08-11
- 摘要：The cyclotron-resonance is a standard technology that determines the conductive electron and hole mass in solids.Usually the effective mass of electron is decided according to the cyclotron-resonance frequency confirmed by experiment.It should be noted that the split of cyclotron-resonance spectrum is strongly affected by the coupling of electron-phonon.Many scholars have paid much attention to the cyclotron-resonance of polaron.Zorkani et al.calcuated the ground state energy of bound magnetopolaron using variational method.Wollf et al.investigated the bound magnetic polarons in semiconductors and the bound magnetic polrons in dilute magnetic semiconductors by the optical experiments.Bouhassoune et al.studied that the magnetic field effect on the binding energy of a bound polaron in a quantum well wire.If consider the interaction between phonons of different wave vectors in the recoil process,the magnetic-field dependence of cyclotron resonance frequency,induced potential,the effectirv interaction potential,and the cyclotron-resonance mass of the surface magnetopolaron is obtained by using a linear combination operator and perturbation method by one of the authors.Li et al,calculated the temperature dependence of effective mass of strong coupling magnetopolaron in polar crystals by using different approximation methods.However,the temperature dependence of effective mass of bound magnetopolaron has not been investigated so far.The properties of a strong-or a weak-coupling bound magnetopolaron were discussed by using a linear combination operator and a unitary transformation methods by the present authors.In this paper,temperature dependence of the effective mass of the strong-or a weak-coupling bound megnetopolaron in polar crystals are studied by means of the improved linear combination operator and the Lagrange multiplier methods.The results illustrate that the vibrational frequency and the effective mass of the strong coupling bound magnetopolaron will increase with increasing temperature.The effective mass will decrease with increasing magnetic field and the vibrational frequency will increase with increasing magnetic field.关键词：bound magnetopotaron;effective mass;temperature dependtnce85|76|0更新时间：2020-08-11
- 摘要：Recently,with the quick development of techniques to fabricate material,the physical characteristic of low dimensional material have aroused great interest.The properties of magnetopolaron in quantum dot has been studied by many theoretical and experimental method by many investigators.Zhu and Gu theoretically studied the effect of electric-fields on shallow donor impurities state in a harmonic quantum dot by using effective mass approximation method.The interaction of electrons,confined in a quasi-zerodimensional quantum dot and longitudinal-optical(LO)phonons,placed in a perpendicular magnetic field,was studied by Wendler,et al.within second-order perturbation theory.Magnetic field effects on strong-coupling polarons in a parabolic quantum dot were investigated by Zhu et al.with the Landau-Pekar variational treatment.Zhau and Gu calculated the ground state and the first excited state of the strong-coupling magnetopolaron in a cylinder-shaped quantum dot by using the variational method of Pekar type.Using a very simple trial function with only one variational parameter,the effects of the parabolic confining potentials and magnetic fields on the binding energy of hydrogen impurities in quantum dots were studied indetail by Nguyen et al.By using the method of few-body physics,Xie investigated the binding energy of the ground state of the D- centers in quantum dots in magnetic field.Chen et al.investigated the thickness effect on the shallow donor impurity-bound polaronic energy levels in parabolic quantum dot in magnetic fields by means of the Larsen method.However,the properties of the polaron and the magnetopolaron in quantum dot has not been investigated by a linear combination operator method so far.The ground state binding energy and the mean number of optical phonons in the cloud around electron of the polaron and the magnetopolaron in parabolic quantum dot were calculated by the method of a linear-combination operator by the present authors.The purpose of this present paper is to explore the effect of the magnetic field B,the electron-phonon coupling strength α,the confinement strength ω0 and the variational parameter p0 on the properties of the weak coupling magnetopolaron in parabolic quantum dot.The relation between the vibration frequency λ and the interaction energy Hint of the magnetoploaron in parabolic quantum dot with the magnetic field,the confinement strength and the electron-phonon coupling strength were derived by using an improved linear combination operator method.Numerical calculations for GaAs crystal show that the vibration frequency λ and the interaction energy Hint of the weak coupling magnetopolaron in parabolic quantum dot will increase with increasing the confinement stregth ω0,the vibration frequency λ will increase with decreasing the variational parameter and the cyclotron frequency,whereas Hint increases with increase of p0,and Hint increases with decrease of ωc.关键词：quantum dot;magnetopolaron;improved linear combination operator73|63|0更新时间：2020-08-11
- 摘要：With quite broad ultraviolet (UV) absorption and emission spectra,the 4fN-15d energy levels of trivalent rare earth ions doped in hosts are possible and perfect upper laser levels for tunable UV laser.In order to obtain upconversion UV laser based on 5d levels,it is necessary and interesting to investigate the excitation behaviors of 5d levels by upconversion pump.In this paper,a theoretical study for the kinetics of frequency upconversion excitation of Pr3+ 4f5d level in Yb3+:Pr3+:ZBLAN fiber is performed by using the population rate equations and related transition theories.Yb3+ ions pumped by the first pump beam (λ1=980 nm) sensitize the excitation of Pr3+ 3P0 level through the energy transfer processes and the second pump beam (λ2=329 nm) realizes Pr3+ 4f5d excitation from 3P0.The distributions of the pump beam intensities and the normalized population densities along the fiber,the effective fiber lengths under different pump intensities and Pr3+ concentrations are calculated.The dependence of 4f5d fluorescence intensity on the incident intensity,fiber length and Pr3+ concentration are discussed.Pumping efficiency as a function of the pump intensity and Pr3+ concentration is also given.The calculated results show that the intensity of both λ1 and λ2 linearly decrease along the fiber and this decrease becomes fast with increasing Pr3+ concentration.Under the pump intensities assumed here the 4f5d population density does not change in the whole pumped region (i.e.,the effective fiber length) where both pump beams exist.This means the 4f5d excitation under the used pump intensities is saturated.The effective fiber length is in proportion to the pump intensity and in inverse proportion to dopant concentration.It is found that higher dopant concentration is favorable to get large 4f5d fluorescent intensity.The pump efficiency increases with the concentration and pump intensities,but the saturation effect will occur when the pump intensities are too large.The results indicate that the upconversion excitation of Pr3+ 4f5d in Yb3+:Pr3+:ZBLAN fiber can be effectively achieved by pump of the two beams.The calculated results may be helpful to further theoretical or experimental study of upconversion UV laser based on 5d levels in rare earth doped optical fibers or bulk hosts.104|60|2更新时间：2020-08-11
- 摘要：Tellurite glass has attracted considerable attention and development effort as a host for broad EDFA and EDWA.But the phonon energy of tellurite glass is relatively low as 770 cm-1,thus,the4I11/2→4I13/2 nonradiative decay is too slow to allow pumping at 980 nm.Tungsten-tellurite glass has higher phonon energy of 930 cm-1,which makes it possible pumping at 980 nm.The 1.5 μm emission bandwidth of Er3+ in tungsten-tellurite glass is also broad.The spectroscopic properties of Yb3+/Er3+-codoped TeO2-WO3-ZnO (TWZ) glasses were investigated,too. The Yb3+/Er3+-codoped TWZ glasses were prepared by traditional melting-quenching method.The absorption cross-section was calculated based on measured absorption spectra at room temperature.The emission cross-section was calculated by McCumber theory.The peak values of absorption cross-section and emission cross-section at 1.5 μm are 0.78 pm2 and 0.90 pm2,respectively.The 1.5 μm emission spectra,upconversion emission spectra and fluorescence lifetimes of Er3+,excited at 970 nm,were also measured.The dependence of Yb3+ doping concentration on the 1.5 μm emission and upconversion luminescence of Er3+ was studied.The calculated energy transfer efficiency from Yb3+ to Er3+ in Yb3+/Er3+-codoped TWZ glasses is about 65%.Yb3+-codoping can enhance the 1.5 μm emission intensity effectively.The optimum Yb3+ doping concentration is about 7.28×1020 ions/cm3,which is triple of the Er3+ doping concentration.The emission bandwidths of Er3+ at 1.5 μm in Yb3+/Er3+-codoped TWZ glasses are broad and the obtained full width at half maximum is between 67 nm and 72 nm.Three upconversion emission bands centered at about 533,547 and 668 nm,were observed.The three emission bands originate from the radiative transitions2H11/2→4I15/2,4S3/2→4I15/2 and4F9/2→4I15/2,respectively.The green and red upconversion emission are both double-photon process.With the increasing of Yb3+ doping concentration,the green and red upconversion emission intensity both increase.This can be ascribed to the increased energy transfer rate from Yb3+ to Er3+.关键词：Yb3+/Er3+-codoped;tungsten-tellurite glass;spectroscopic properties;upconversion emission91|94|0更新时间：2020-08-11
- 摘要：The reflectivity characteristics of Distributed Bragg Reflector (DBR) are described by an equivalent F-P cavity method.The DBR structure is grown by MOCVD.The GaAs buffer layer is grown on the n-type GaAs substrate,its thickness is 500 nm.The DBRs is consisted of Al0.12Ga0.88As/Al0.9Ga0.1As and the optical thickness of each layer is of quarter wavelength.The top DBR is consisted of 22 pairs,and the bottom DBR is consisted of 34 pairs.The active region is consisted of three undoped multiple quantum wells structure of GaAs/Al0.3Ga0.7As.The p-type dopant is carbon and the n-type dopant is silicon. The reflectivity of DBR with asymmetric structure is calculated and discussed.The structure of 850 nm center wavelength of the DBR reflectance spectrum was designed.The thickness of DBR structure was determined by its reflectivity and center wavelength. The experimental results indicated that this is an effective method for the optimal design of DBR.As a result in practice,it is easy to output laser when the periodicity of reflector in bottom DBR structure is about 30 pairs and periodicity of reflector in top DBR structure is about 20 pairs. Be compared with the experimental results,it is found that the simulative results are similar with the experimental results.It indicates that the simulative results are reliable and it can also be used for simulating some others.The experiences indicated that the simulation is an important guideline for developing and fabricating the DBR.关键词：distributed Bragg reflector (DBR);F-P cavity;reflectance characteristics114|106|2更新时间：2020-08-11
- 摘要：ACCENT PN4400 ECV (Electrochemical C-V Profiler) is specially designed for the semiconductor materials with wide band gap.At present,it is mainly used for GaN.GaN is difficult to etch normally.But if it was lit by UV light,it can be etched by H2SO4.According to our experience,this make ECV to be specially suitable for GaN.Becase no lighting no etching,uniform light makes uniform etch.What should be point out is that this rule is only limited to GaN:Si.For our wafer with whole LED structure,it is very difficult to get uniform etch on p layer.To get uniform etch,it is still very important to select carefully the ecth and measure conditions.One tip is that you must stop the etch process temperarily to check and change the conditions,and from time to time,stop to elimit the bubbler near the etch hole edge by an injector filled with H2SO4. Because it will take a long time to wait the LED chip result after wafer growth.It will be better to find out a relationship between the chip result and the ECV result.Two samples with different buffer technology produced in the MOCVD system made by Thomas Swan Ltd.were measured by PN4400 ECV.From the relation of carrier concentration vs.depth,it is easy to see that the lowest carrier concentration given by ECV can be used as a standard to judge the crystal quality.Two samples were made into LED chips.It is known to us all that the Ir of LED has a close relationship with the crystal quality.The sample with the lower minimum carrier concentration gives lower Ir.Besides the carrier concentration distribution,ECV profiler can also give a lot of other information abou GaN.So as the experience accumulates,we believe that ECV profiler can give some important information about GaN wafer before it becomes LED chips.Silicon dopping technology is very important for fabrication of GaN LED.Certainly,the silicon will diffuse in GaN at high temperature.So it is important to find the silicon diffusion coefficient in GaN.We try to do this by ECV.By introducing a diffusion model and Gaussian fitting,we estimate that the silicion diffusion coefficient in GaN at 1 030℃ is below 4.3×10-18 m2/s.关键词：silicon diffusion;GaN;ECV104|88|0更新时间：2020-08-11
- 摘要：The AlGaInP/GaInP multiple quantum wells red LED wafers were grown by EMCORE GS/3200 LP-MOCVD.Properties of these wafers were investigated by ECV and photoluminescence measurements.The influences of thermal annealing on the characteristics of AlGaInP/GaInP multiple quantum wells LED wafers were studied. The AlGaInP/GaInP multiple quantum wells LED wafer for thermal annealing experiments consisted of a 0.5 μm n-GaAs buffer layer with carrier concentration of about 5×1017 cm-3,a 0.5 μm n-(Al0.7Ga0.3)0.5In0.5P cladding layer with carrier concentration of about 3×1017 cm-3,a (Al0.3Ga0.7)0.5In0.5P/Ga0.5In0.5P MQW active region,a 0.5 μm p-(Al0.7Ga0.3)0.5In0.5P cladding layer with carrier concentration of about 6×1017 cm-3,and a 4.8 μm p-GaP current spreading layer with carrier concentration of about 5×1018 cm-3.The wafer was split into six pieces.These six pieces were annealed under different temperatures within 460～780℃ respectively for 15 min in nitrogen.Compared with as grown samples,the hole carrier concentration of GaP layer in LED wafer increased from 5.6×1018 cm-3 to 6.5×1018 cm-3,and the hole carrier concentration of AlGaInP layer increased from 6.0×1017 cm-3 to 1.1×1018 cm-3,when wafer was annealed under 460℃ for 15 min in nitrogen.The hole carrier concentration of GaP and AlGaInP layers did not obviously change when the annealed temperature was increased to 700℃.However,the hole carrier concentration of GaP layer and AlGaInP layer decreased to 8×1017 cm-3 and 1.7×1017 cm-3 when wafer was annealed under 780℃ for 15 min.And the diffusibility of Mg atoms was enhanced and the undoped AlGaInP/GaInP MQW was p type conductance when the annealing temperature increased to 780℃.The peak wavelength and FWHM did not obviously change when the annealing temperature was lower than 780℃.However,the PL peak intensity from MQW was about 2 times stronger than that of as grown sample when wafer was annealed under 780℃ for 15 min.关键词：AlGaInP;AlGaInP/GaInP MQW;MOCVD;ECV;photoluminescence111|76|0更新时间：2020-08-11
- 摘要：Both CdS and ZnS crystals are Ⅱ-Ⅵ semiconductors and photonic materials having the direct band gaps.Since the wavelength corresponding to the band-gap of CdS is green 500 nm that is very sensitive for human eyes,the CdS thin film is useful for the sensor and the light source.For the CdS thin film produced by pulsed laser deposition (PLD),we first demonstrated the laser oscillation at room temperature excited with He-Cd laser.On the other hand,ZnS has been used for the fluorescence materials with the various doped elements.The band-gap of ZnS is so large (3.6 eV) that has been applied for the quantum well,the blue LED and the optical waveguide.Zn1-xCdxS alloy thin films were prepared on quartz substrate by low-pressure metalorganic chemical vapor deposition (MOCVD).The x values of Zn1-xCdxS are 0,0.02,0.44,0.59,0.83,0.91 and 1.X-ray diffraction (XRD) spectra indicate that all the as-grown alloys with hexagonal wurzite structure was obtained.As the Cd content increases,the luminescence peaks of the samples redshift from 3.66 eV to 2.43 eV in the photoluminescence (PL) spectra.Based on the PL peak position of the alloy with different Cd composition,the relation of Zn1-xCdxS emission peak with x was obtained as Eg(Zn1-xCdxS)=3.61-1.56x+0.38x2.The dependence of the PL peak position and the full width at half maximum(FWHM) of the diffraction peak and PL peak on Cd composition were also discussed.It is found that when x increases from 0 to 1,the PL peak position changes from 3.66 eV to 2.43 eV;but the FWHM increases and reaches a maximum when x=0.83,then it decreases sharply.关键词：Zn1-xCdxS;MOCVD;XRD;PL89|59|0更新时间：2020-08-11
- 摘要：F-passivated ZnO nanocrystalline films were prepared from thermal oxidation of ZnF2 films.The ZnF2 films were deposited on a Si wafer by electron beam evaporation technique.X-ray diffraction and X-ray photoelectron spectroscopy were used to study the structural changes of ZnF2 as a function of oxidation temperatures.When the ZnF2 film was oxidized at 400℃ for 30 min,a polycrystalline hexagonal wurtzite structure of ZnO:F was obtained.The room-temperature photoluminescence spectrum of the ZnO:F film showed a strong near band edge ultraviolet emission located at 379 nm with a narrow linewidth of 73 meV and a very weak visible emission associated with deep level defects.The results indicated that the presence of residual F ions in ZnO film can dramatically decrease the visible emission and increase the ultraviolet emission of ZnO.关键词：ZnO:F;XRD;XPS;photoluminescence103|74|1更新时间：2020-08-11
- 摘要：Zinc oxide (ZnO) has attracted interest owing to its potential applications including nonlinear optical devices,blue-violet light emission devices,buffer layer for GaN-based devices,visible range transparent electrode for solar cell,display and surface acoustic wave devices.Inspired by the application of ZnO,numerous studies have appeared on the luminescence of ZnO.Two emission bands are usually found.One is a narrow UV emission band and the other is a broad visible emission band at approximately 520 nm.The UV emission from ZnO is commonly attributed to band-to-band or near band edge emission.The nature of the visible emission has been the subject of much research,however,the mechanism behind the visible luminescence has been very difficult to establish.During the past years,oxygen vacancies have been assumed to be the most likely candidates for the recombination centers involved in the visible luminescence of ZnO.Recently,Van Dijken et al.proposed a model for the kinetic mechanism behind the visible emission of nanocrystalline ZnO particles;the visible emission of ZnO was a recombination of a shallowly trapped electron with a deeply trapped hole and the surface state plays an important role during the recombination process.To study the effect of surface defects on luminescence we used polyethylene oxide (PEO) as capping polymer molecules to achieve the surface-modified ZnO nanoparticles.ZnO nanoparticles surface modified by polyethylene oxide(PEO)were fabricated and the influence of surface-modification on optical properties of ZnO were studied.The PL spectra showed two emission bands:one was UV emission,the other was deep level emission related to oxygen vacancies.When the PEO content increased,the ratio of the UV emission to the deep level emission increased.When the PEO content was the largest,the ratio is 31.5,which is much bigger than that of the pure ZnO nanoparticles.So when ZnO nanoparticles were modified by PEO,the UV emission efficiency was enhanced and the quality of the ZnO nanofilm was improved.关键词：PEO;ZnO;surface-modification;deep level emission102|86|2更新时间：2020-08-11
- 摘要：Complex films of mercapacetic acetic (MPA) and ZnO were formed by adding ZnO nanocrystals film on Si substrate to the chloroform solution of mercaptoacetic acetic.The Zn-S bond was formed,which may be demonstrated by XPS.The fluorescence properties of ZnO thin film has been influenced by the amount of coated mercaptoacetic acids.With increasing the amount of mercaptoacetic acids,the ratio of coated surface increased.By characterization of photoluminescence,we found that the free exciton and bound exciton decreased.To those phenomena,we explained them by the electron transfer between ZnO and mercaptoacetic.Firstly,when bonds between ZnO and mercaptoacetic were formed,the electrons excited wouldn't combine with holes and the electrons would transfer into the level of mercaptoacetic acids.Thus,the ratio between electrons and holes of ZnO decreased and the intensity of its photoluminescence decreased.Secondly,the amount of mercaptoacetic acids would influence on the ratio of electrons and holes of ZnO.The mercaptoacetic acids increased,the ratio of electron transfer enhanced.So we may obtain the data of photoluminescence that the intensity of photoluminescence decreased with increasing the amount of mercaptoacetic acids.Otherwise,the profile photoluminescence of ZnO modified with mercaptoacetic acids showed that the intensity of ZnO photoluminescence decreased gradually with the distance of ZnO layer near to the surface.关键词：ZnO nanocrystal thin film;mercapacetic acetic;electron transfer89|80|1更新时间：2020-08-11
- 摘要：ZnO film is of great interest for short-wavelength optoelectronic application because ZnO semiconductor with a wide band gap of 3.34 eV has a large exciton binding energy of 60 meV at room temperature.However,there is almost no application based on the active function as a compound semiconductor.The primary reason is because most active functions in semiconductors come from the characteristic properties of p-n junction but the preparation of p-ZnO is in difficulty.There is of interest in the p-n heterojunction diode fabricated by using a combination of p-type oxide conductor and n-type ZnO.In this paper Cu2O was chosen to compose p-n heterojunction with n-type ZnO.Cu2O as a p-type direct-gap semiconductor with a bandgap energy of 2.1 eV,has been regarded as one of the most promising materials used for optoelectronic applications recently.Cu2O is a potential photovoltaic material due to the low cost,non-toxicity and the natural abundance of the base material.Furthermore,Cu2O is one of the few oxide semiconductors that are p-type.The nature of the p-type conductivity of Cu2O is originated from the presence of Cu vacancies which form an acceptor level above the valence band.The heterojunction was prepared by two step cathodic electrodeposition.Electrodeposition is a simple and convenient method.It has several advantages also,such as low processing temperature,higher deposition rates,controllable film thickness and morphology.Uniform films can be formed on various substrates with complex shapes and employed with inexpensive equipments.The kinetics of electrodepostion of Cu2O was discussed.X-ray diffraction,scanning electron microscopy,UV-Vis transmittance technologies were used to investigate the structural properties of the heterojunction.The electrical properties were also studied by measuring the I-V characteristic.The results showed that this simple electrochemical route was a favorable method to fabricate Cu2O/ZnO heterojunciton.关键词：ZnO;Cu2O;heterojunction85|75|2更新时间：2020-08-11
- 摘要：Ab initio calculations of fluorescence spectra have been scarcely reported in references.The fluorescence of three heterocyclic organic compounds with five-membered ring have been studied by B3LYP method of DFT,in this paper.Geometric configurations of three heterocyclic organic compounds are optimized by B3LYP method at the level of 6-31G* and there are no imaginary frequences in vibrational analyses.On this basis,the mechanics of electronic transition in these molecules has been discussed through molecular orbital analysis.The results show that the transition between HOMO and LUMO in the three compounds is the electronic transformation from C1,C2,C3 and C4 to hetero-atoms (N atom in pyrrole,O atom in furan and S atom in thiofuran).The fluorescence spectra of these three compounds have been calculated by CIS method at the level of 6-31G*.The results of calculation are essentially consistent with the experimental values.This paper should be valuable for ab initio calculation of electronic spectra of organic compounds.关键词：five-membered ring;quantum chemistry;fluorescence spectra;single excitation configuration interaction(CIS)101|93|0更新时间：2020-08-11
- 摘要：Recently,9 new soluble organic small molecular electroluminescent materials,derivatives of Alq3,have been synthesized in our laboratory and Almq2-OH of these materials has very good blue electroluminescent characteristics.To investigation further electroluminescent properties of these materials we focus on the measurements of energy level structure parameters of the 9 soluble organic small molecules using cyclic voltammetry(CV).The electrochemical oxidation potentials (Φp) and reduction potentials(Φn) of these organic small molecular were measured by a 273A model potentiostat/galvanostat at a potential scan rate of 50 mV/s.In each measurement case,the organic small molecular film on a conducting glass substrate was used as the working electrode;platinum wire was used as counter electrode.All the potential values are referred to Ag/AgCl/Cl- as the reference electrode.The energy levels corresponding to the highest occupied molecular orbital(HOMO),lowest unoccupied molecular orbital(LUMO) and energy gap(Eg) of these small molecules were determined from the onset potentials for oxidation (Φp) and reduction(Φn),respectively,and HOMO energy level(EHOMO),LUMO energy level(ELUMO) and Eg are calculated through following empiric formula,EHOMO=-e(Φp+4.44)(1)EHOMO=-e(Φn+4.44) (2) Eg=-eΔΦ (3)Where ΔΦ=Φp-Φn,e is elementary charge.The experimental values of the electrochemical energy gap of Alq3 and its derivatives are in good agreement with the results determined by the optical absorption spectroscopy.The experimental values of EHOMO,ELUMO and Eg of Alq3 are in excellent agreement with the values quoted from literatures.It was shown that the HOMO,LUMO energy level and Eg obtained from CV measurements for these organic small molecular are feasible,and the measurement data obtained are reliable.In order to perfect organic light-emitting diodes the energy band structure parameters of electroluminescent materials are of critical important to the selection of cathode and anode materials.The recombination mechanisms of electrons and holes in these organic materials will be explained by using these energy level structure parameters.关键词：organic electroluminescent material;cyclic voltammetry;HOMO and LUMO energy level;energy band gap144|153|3更新时间：2020-08-11
- 摘要：The interface between metals and organic semiconductors plays a central role in the physics of polymer light-emitting diodes.In addition,the asymmetry in the work function of the two electrodes is responsible for the polymer light-emitting diodes rectifying behavior and governs the injection of carriers in polymer.In order to fabricate efficient devices and to minimize injection barriers,the low work function cathodes and high work function anodes are desirable.Ideal electrode materials have been difficult to obtain,however,an incorporation of injectint inter-layers at electrode/polymer interfaces has been used as an alternative route towards enhanced carrier injection.The performance of polymer light-emitting diodes with inserting metal fluoride insulating layer between the metal cathode and active polymer was studied.As for the polymer light-emitting diodes,optimization of charge injection lies in the dominant factors for substantive improvement performance.Since it is minority carriers dominate the recombination thus the radiation,their injection takes priority over that of majority carriers.Generally in semiconducting polymers,holes are majority carriers while electron iniection.there are two commonly used stratagems in cathode fabrication.One is to employ low work function metals such as barium and calcium as cathode though they are susceptible to degradation upon water vapor and oxygen.The other choice is proposed to insert an insulating thin layer usually metal fluoride between polymer/electrode interfaces to build a bilayer cathode.Proper inserting of insulating layer would lead to improvement in the overall working perfomance.But the thickness of the insulating layer is a fatal factor that influences the enhancement effect.As show in the experiment result,the LiF/Al double-layer-cathode devices are capariable with Ba(Ca)/Al electrode devices in luminescence performance.Band bending and injection potential decrease of minority carrier caused by the inlay of metal fluoride insulating layer,are proposed to be responsible for the enhanced electron injection and improved performance in polymer light emitting diodes.关键词：polymer light-emitting diodes;MEH-PPV;cathode;LiF98|85|2更新时间：2020-08-11
- 摘要：A series of dinuclear complexes with different Eu3+ to Tb3+ ratios with p-phthalic acid (L') and ligand of 18 crown 6(L) have been synthesized.Elemental analysis,IR absorption spectra and fluorescence spectra have been studied respectively.The compositions of the complexes were confirmed to be(Eu1-xTbx)2L2L'(ClO4)4·H2O(6+3x).Smaller Tb3+ coordinated with water molecules,which were hydrogen bonded with crown ether while Eu3+ coordinated with crown ether directly may be concluded. Shimadzu FR-5301PC fluorescence spectrophotometer was employed to measure the luminescence spectra at room temperature.As results showed the excitation wavelength changed with the molar ratios of Eu3+ to Tb3+.The optimum excited wavelength is at the same position(298 nm) when contents of Tb3+ is 100% and 90%,respectively.It changes to 254 nm when Tb3+ content decrease to 70% and Eu3+ content rise to 30%.The measurement results of the emission spectra of the complexes indicated that the emission peaks of Tb2L2L'(ClO4)4·12H2O consisted of four groups of emission peaks and Eu2L2L'(ClO4)4·6H2O has three,while (Eu1-xTbx)2L2L'(ClO4)4·H2O(6+3x) has five.The previous are as following:peaks at 490.0,545.8,585.6 and 621.0 nm are as the Tb3+ ions5D4→7FJ(J=6,5,4,3) transitions correspondingly,among them the emission from 5D4→7F5 is the strongest belonging to hypersensitive transition(ΔJ=2).The latter are following:first group,578.6 nm belongs to 5D0→7F0 transitions of Eu3+,the second group,588.2 nm and 592.2 nm,both belong to 5D0→7F1 transitions of Eu3+,the third group,613.6nm and 618.2 nm both belong to 5D0→7F2 transitions of Eu3+.The last one:they appear at about 490,545,579,585 and 620 nm.The first and second fluorescence bands centered around 490 nm and 545 nm corresponding to 5D4→7F6 and 5D4→7F5 transitions of Tb3+ ions.Overlapped peaks at 585 nm and 620 nm were found caused by interaction between 5D0→7F1,5D0→7F2 transitions of Eu3+and5D0→7F4,5D4→7F3 transitions of Tb3+.Variance of fluorescence spectra emission peaks showed that there are interaction between Eu3+ ions and Tb3+ ions in (Eu1-xTbx)2L2L'(ClO4)4·H2O(6+3x). The fluorescence emission intensity of Tb3+ (5D4→7F5) in Tb2L2L'(ClO4)4·12H2O was 1 313.6 comparing with 29.8 of Eu3+ (5D0→7F2) transitions in Eu2L2L'(ClO4)4·6H2O.Concluded from R=Id/Ic(Id=values of the fluorescence emission intensity determined,Ic=calculated values) is below 1.0 at 490 nm and 545 nm (corresponding to Tb3+5D4→7F6 and5D4→7F5 transitions) even at 585 nm.However when ratio of Eu3+ and Tb3+ is 0.9:0.1～0.7:0.3,the R values for peaks at 579 nm and 620 nm are higher than 1.0 collectively,Eu3+ will quench Tb3+ fluorescence while Tb3+ will sensitize Eu3+.关键词：complexes of rare earth ions(Eu-Tb);18-crown-6;p-phthalic acid;fluorescence75|83|1更新时间：2020-08-11
- 摘要：The observation of visible photoluminescence (PL) from porous silicon (PS) at room-temperature has stimulated many studies for potential applications in silicon-based optoelectronics.And the PL characteristics of PS is one of the most concentric problems.But the PL mechanism is still a controversial issue.In order to have a further study on the PL characteristics of PS luminescence and discuss the PL mechanism,this letter reported the optical properties of transition-metal (copper) doped porous silicon by immersion plating in metal ion solutions (CuSO4).Immersion or electroless plating refers to the plating of soluble metal ions onto a base material without applying a bias.In order to research the influence on photoluminescence of PS by copper-doping,the photoluminescence spectrum and the Fourier transform infrared (FTIR) spectroscopy were measured.Comparing the PL spectrum of the as-deposited porous silicon with the Cu-doped PS,the PL intensity of the Cu-doped PS decreased dramatically and the PL peak locations had a blue shift obviously.That is to say,there was a photoluminescence quenching of porous silicon by immersion plating in copper sulfate solution.And the PL intensity decayed more dramatically with the increasing concentration of the copper sulfate aqueous solution and the immersion time.Fourier transform infrared spectroscopy indicated that:(1) the intensity of the SiHx stretching absorption peaks (2 090～2 050 cm-1) and the Si-H stretching absorption peaks (620 cm-1) decreased after immersion plating;(2) There was a strong absorption at 1 109 cm-1 due to Si-O-Si in the Cu-doped samples.Studies revealed that the quenching effect of Cu-doped PS may be related to the decrease of Si-H bonding and the nonradiative recombination center played by Cu induced surface electronic states.But the blue shift of the PL peak locations may results from the existence of oxidation on the surface of Cu-doped porous silicon.All of above experiments indicated that,the PL of porous silicon was quenched by copper-doping;and metal deposition occurred simultaneously with the oxidation of silicon to silicon dioxide (SiO2).关键词：porous silicon;photoluminescence;FTIR;immersion plating;quenching108|105|1更新时间：2020-08-11
- 摘要：Oxidizing porous silicon in proper condition is a good approach to improve PS photoluminescence intensity.The article for the first time raised a new anodic oxidized technology of PS.We used electrolyte containing CH3CSNH2 to oxidize initial PS,and found that this method can improve the quality of photoluminescence,it can not only enhance the PL intensity greatly,but also increase the photoluminescence stability.Then we studied the oxidizing conditions(current,time,temperature etc.)which affect photoluminescence intensity and stability of PS and gave reasonable explanations.The small oxidizing current can repair the nanostructure of PS,the appropriate oxidizing time can limit the probability of nonradiative recombination,while the optimum oxidizing temperature is propitious to the transit of charge which can make the concentration of electrolyte balanceable,hence,the photoluminescence of oxidized PS is improved evidently.We discovered that the anodic oxidized technology of PS made the integral intensity of photoluminescence enhanced 18 times when in the optimum oxidized conditions of (1 mA,10 min,60℃).关键词：porous silicon(PS);wet oxidized;photoluminescence99|85|0更新时间：2020-08-11
- 摘要：Due to the importance of blue-green luminescence of silicon basis in color display and integrated apparatus,people begin to pay attention to this scientific research.The emission wavelength of coumarin dyes lay over 420～580 nm,transmit eyeable blue-green fluorescence.Because this kind of dyes belongs to laser dyes,it has good performance of luminescence,such as:high luminescence efficiency,fast response rapidity,short duration etc,these performance are in favor of information transmission and collection.Using the speciality of porous silicon:the structure of particular nanoporous,the mortal surface area,the strong capacity of absorption,the sensitive characteristic of surface luminescence,coumarin 102(C102) was impregnated into porous silicon.In this way,the composite system of porous silicon embedded C102 was obtained. Porous silicon was obtained by electrochemistry,anodization was conducted at a constant current using a DC stabilized power and flow supply,the specimens were prepared and measured in the ambient air.It was found that the fluorescence spectra of C102 embedded in PS was similar to the fluorescence spectra of C102 in ethanol,and the symmetry of spectra was improved.It was also found that energy transfer occurred between impregnated dye and porous silicon,the photoluminescence of the embedded film had better stability and reserved excellent optic characteristic of laser dyes.The experimental results suggested that the porous silicon embedded C102 might be a better approach of realizing the blue-green photoluminescence on silicon basis.关键词：porous silicon;coumarin102;PL spectra;energy transfer82|82|1更新时间：2020-08-11
- 摘要：Molecule interaction between naphthaquinones and thiazole was studied with F1-rster theory and experimental investigation.It was found that the excitation spectrum taken from the thiazole derivative polythene resin film has a peak around 602 nm with a width of 30 nm,which overlaps the emission band of naphthaquinones derivative polythene resin film.This suggests that energy transfer can occur between thiazole and naphthaquinones molecules.So new luminescence materials could be made by changing the chromophore into the fluorophores.This work is very significant for the development of the white LED by light conversion.关键词：molecule interaction;energy transfer;fluorescence spectrum;excitation spectrum80|61|0更新时间：2020-08-11
- 摘要：Polydiacetylene with the substantial π-electron delocalization along the main chain backbones is one promising nonlinear material for application and fundamental properties of nonlinearity.Utilizing LS technology,uniform thin film with a desired thickness can be obtained easily and inexpensively,which makes convenience for optical device applications.Therefore many attempts have been performed to improve nonlinear optical (NLO) properties of polydiacetylene LS film.In this paper,an eight-monolayer film of poly-10,12 pentacosadiynoic acid (poly-PCDA) about 26 nm thick was prepared on glass substrate using Langmuir-Schaefer method.Then,the third-order NLO properties of poly-PCDA were investigated by Z-scan technique using a femtosecond pulse laser with the pulse duration of 100 fs at 800 nm.A self-focused effect was observed.And the nonlinear refractive index γ,TPA coefficient β,real part of third-order NLO susceptibility Reχ(3) and imaginary part of third-order NLO susceptibility Imχ(3) of ploy-PCDA were calculated.A very large value of third-order NLO susceptibility χ(3)=5.33×10-9esu was detected under the average incidence power of 145 mW.This magnitude reaches the same order as that of polydiacetylenes crystal or mictocrystal.We investigated the factors contributed to third-order NLO susceptibility and ascribed primarily them to two factors.First,π-electron aberrance induced by femtosecond laser can be a key mechanism for the third-order NLO poly-PCDA LS film.Second,a large conjugated system requires that the molecule should be as planar as possible without too much torsion or distortion of monomer units in the chain.In our case,longer conjugated chain may form without ligand interference.The high nonlinearity and uniform large area film makes poly-PCDA LS film particularly interesting and attractive for optical device designs.关键词：poly-10;12 pentacosadiynoic acid;nonlinear optical;femtosecond laser pulse;Z-scan99|75|0更新时间：2020-08-11
- 摘要：When a medium was excited by a laser,the thermal effect always existed.Especially for a laser whose pulse width was beyond ns.or the sample had large absorption,the effect could not be neglected.So the investigation of the thermally induced optical properties of a compound was very important.The thermally-induced nonlinear refraction index changes of a sample always covered the change of quick electron effect when the refraction index was measured by some techniques.The thermally-induced third-order optical nonlinerity property of the coordinated compound of three kinds of transition metals Ni,Cu and Pd was studied by Z-scan technique for the first time.Both 488 nm and 632.8 nm CW laser were used for excitation.The result showed that the optical nonlinear refractions of the three compounds under CW laser resulted from the thermal effect,and they had no nonlinear absorption.By combining experimental curves and the thermal effect theory,we calculated the thermoptical coefficient dn/dT and the thermal-induced refractive index n2 of the compounds.By comparison,it could be discovered that the thermoptical coefficient dn/dT and the thermal-induced refractive index n2 of the three compounds were different from each other under different excitation conditions.In general,the values of dn/dT and n2 under 488 nm laser excitation were bigger than those under the excitation of 632.8 nm laser,this was in according with other paper's results.Moreover,the values of dn/dT and n2 of the compounds also depended on the linear absorption under certain condition.The stronger the absorption,the bigger the values.Finally,the atomic number of the central metal atom of the coordinated compounds influenced on the values too.If the central metal atomic number was bigger,then the thermoptical coefficient and the thermally-induced nonlinear refractive index of the compound were bigger.关键词：coordinated compound;thermooptical coefficient;thermally-induced optical nonlinearity104|72|1更新时间：2020-08-11
- 摘要：A series of benefits in the field of the solid state compounds synthesis by solvothermal technology have been developed from the water-thermal method.The solvent,water in the hydrothermal reaction was replaced by the organic solvent in the solvothermal reaction.The organic solvents have lower boiling point,different permittivity,polarity and viscosity.It was convenient to design a new synthesis processes in the different solvents,and to produce the goal products.Many nanosized metal chalcogenides crystallites such as CdS,In2S3,Sb2S3,CoS2 and SnS2 have been synthesized by choosing the non-aqueous solvent such as benzene,toluene,tetrahytrofuran,1,2-dimethoxyethane,ethylenediamine at a lower temperature.Nanosize CdS semiconductor particles and PANI film were synthesized using the solvothermal technique and the electro-chemistry method onto the indium-tin oxide glass (ITO) respectively.The CdS structure was characterized by means of XRD,TEM and ED techniques.The nanoparticles were doped on PANI film by dipping process,and the self-assembled nanoparticles-PANI composite film was acquired.The photoelectric properties of the self-assembled film was studied by PL and Z-scan method.The result concluded that the fluorescence radiation and nonlinear absorption coefficient can be unambiguously enhanced when PANI film was decorated with CdS nanoparticles.关键词：nano;polyaniline;composite film;semiconductor93|102|4更新时间：2020-08-11
- 摘要：It has been in great use for the integrated rod illumination system in integrated rod projection display field because of its simple structure,low cost,high efficiency and uniformity.The principle is that with the application of the ray reflected several times in integrated rod the ray can form well-proportioned rectangular illumination in the end of the rod.With the reduction of the light modulator dimension,the advance system is required to analyze and design with the concept of Etendue value. It is complicated to analyze data of the light source.In this paper the solid source model is induced and with the space distribution and angular distribution of the intensity,the model method is given.It is helpful to estimate and simulate the uniformity,optical efficiency and optimum Etendue value by exactly analyzing.Expanding the reflection ray in integrated rod by law,the merge and the center of the rod can be found because different ray has different location.These rays have different reflection times before they reach the end surface of the rod also.The formulation and the function of rod uniformity are given. The Etendue value is reduced with the reduction of modulator dimension.So how to reduce Etendue value but keep the efficiency is a big problem for the illumination and light source design.An improved light source reflector,which can reduce Etendue value effectively,is introduced.It is fit for 1.3～1.8 cm light modulator judged by computer simulation.关键词：compound reflector;integrator rod;illumination system;Etendue;optical efficiency113|95|0更新时间：2020-08-11
- 摘要：OLED (organic light-emitting diode) is an important member of flat panel displays (FPD).Due to its many merits such as high luminance,low drive voltage,high response speed and variety of emission colors,etc.,OLED attracts worldwide attention in the fields of science and industry.At the present time progress in making long life and high stability has been made,but drive circuit for OLED is not very perfect,and chips for OLED are very simple,and the functions of chips are very simple.Meanwhile the functions of drive circuit chips for LCD are very perfect and the price is very cheap,so we determine to design a drive circuit for TFT-OLED with TFT-LCD drive chips.Firstly,the article compares the driving principle of TFT-LCD and the one of TFT-OLED,and finds that two driving principles are very resemble,so it is possible changing the drive chip of TFT-LCD and making it drive TFT-OLED.Then we choose two types of TFT-LCD chips fabricated by Samsung.One is the 120/128 channels TFT-LCD gate driver S6C0655,the other is the 6 bit 480 channels source driver S6C0671.After analyzing the chips,we find that the driving timing,display data,output driving voltage and currency of the chips meet the need of our color TFT-OLED completely.The voltage on liquid crystal pixel is alternating voltage,but the voltage on OLED pixel is direct voltage,so we adjust the input on POL pin,let it maintain low voltage always.We choose 80 channels of S6C0655 and 240 channels of S6C0671 because the standard of our color display is 64×3×80.At last,we design a circuit with a piece of MCU,a piece of S6C0655,a piece of S6C0671,a piece of ROM and some periphery circuits.ROM,S6C0655 and S6C0671 are controlled by MCU.Display data are stored in ROM.When the circuit is working,MCU gets the data from ROM and transfers them to S6C0671 and transfers shift pulse to S6C0655 synchronously.关键词：OLED;liquid crystal drive;LCD drive chip102|88|2更新时间：2020-08-11
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