最新刊期
卷 28 ， 期 1 ， 2007
- 摘要：The density of states and band structures of α-V2O5 and Li-intercalated V2O5 (LixV2O5, x=0.5 and 1.0) have been studied using a first-principles calculation based on density function theory with the local density approximation. The results indicate that V2O5 is an indirect-gap semiconductor; the intercalation of Li will not change its way of electron transition. While, the intercalation of Li lowers the energy of conduction band, and then narrows the band gap. At the same time, due to the intercalation of Li, the split-off in the conduction band of V2O5 disappears because of the split of conduction band. The Fermi level of LixV2O5 increases dramatically due to the electron transfer from Li2s to the V2O5 host, which is probably the main reason why the optical band-gap augments with the Li intercalation.关键词：first-principles calculation;V2O5;Li intercalation;electronic structure;optical properties96|112|0更新时间：2020-08-11
- 摘要：Photonic crystals are new manual microstructure materials with periodic refractive indices distribution. The photonic crystals have photonic band gaps analogous to the electronic band gaps in semiconductors. If the frequencies of electromagnetic waves are within the photonic band gaps, they cannot propagate in the photonic crystals. We introduce the new structure in the research of photonic crystal microcavities. Two-dimension square photonic crystal microcavities composed of Al2O3 are studied by plane wave expansion method. The physical mechanism and numerical simulation are detailed. We can obtain the band gap and the frequency of defect mode. The range of defect mode is 470～476nm. The spectral curve of defect mode is given by calculating the quality factor of photonic crystal microcavities. In spectral curve, there are many peak values when transmission wavelength is increased. The highest quality factor achieved at 475 nm. And more study on the effective index of cladding was performed by fully vectorial effective index method. We study the stability of photonic crystal microcavities by effective index method, and obtain the variational curve of effective index. There is a steady field when transmission wavelength is about 475nm. These methods are valuable in the design of optical devices based on photonic crystal cavities. Photonic crystal semiconductor laser and photonic crystal diode can be designed under this guidance.关键词：photonic crystal;point defect;photonic crystal microcavities;effective index116|98|3更新时间：2020-08-11
- 摘要：The purpose of the paper is to study the synthetic effects of the negative quintic nonlinearity of optical fibers and the initial frequency chirps of optical pulses on the frequency chirps and spectra of Gaussian optical pulses. Utilizing the extended nonlinear Schr dinger equation including quintic nonlinearity and neglecting the chromatic dispersion of optical fibers, the frequency spectra and the whole chirps of chirped Gaussian optical pulses are calculated and analyzed. The results show that, when the pulses are initially unchirped, the negative quintic nonlinearity can make the shapes of chirps change from single ‘S’ to dual ‘S’shape and even make the chirps in the central regions of pulses change from positive to negative. In addition, the negative quintic nonlinearity can also make the effects of initial chirps on spectra of pulses change considerably. After overlapping with the chirps caused by nonlinearity, the initial chirps can greatly influence on the energy distribution among the spectral peaks while slightly influence on the number of peaks. For some values of maximum nonlinear phase shifts, it may even occur that, the decrease of the whole chirps makes the number of spectral peaks increase. This investigation will contribute theoretically to the deep development of the optical switching, pulse compression, optical fiber communications, and so on, to some degrees.关键词：nonlinear optics;negative quintic nonlinearity;frequency chirps;power spectra123|68|2更新时间：2020-08-11
- 摘要：Coherent sources of picosecond pulses that are tunable in the near infrared are interesting for many applications and more significantly for fundamental and applied research in nonlinear optics and telecommunications.Optical fiber and waveguide components usually require relatively low-peak-power optical sources for diagnosis or excitation,thus making high-repetition-rate synchronously pumped optical parametric oscillator(OPO)an attractive solution for this application.Quasi-phase-matched OPO based on periodically poled lithium niobate(PPLN)offer a high nonlinear coefficient,low loss,a broad operating range,versatility and large nonlinear optical coefficient(d33~25.2pm/V at 1.064nm)in fabrication techniques.Recently many efforts were devoted to fabricating a periodically poled structure in 5%(mol fraction)MgO-doped LiNbO3(MgO:LN)because of its higher resistance to photorefractive damage and lower coercive field of ~4.5 kV/mm at room temperature(RT)than that of LN,as well as its large nonlinear coefficient,comparable with that of LN.Temperature tuning is a unique feature of OPO,which makes its application scope enlarged.Temperature tuning feature of OPO based upon PPLN is the result that the operating temperature fluctuation of PPLN causes output wavelength shifts due to the changes of the length of PPLN and the refractive index of material.The width of PPLN grating period will change because of the expansion coefficient of material when the operating temperature fluctuates.By using short-pulse field,the periodically poled grating(Λ=30.0μm)was successfully fabricated in 1.0mm thick MgO:LiNbO3(doped 5% MgO).A high-repetition-rate optical parametric oscillator(OPO)based on PPMgLN pumped by a 1.064nm acousto-optically Q-switched Nd:YAG laser.The threshold is 45 mW with pulses repetition rate 1 kHz at room temperature.Under the condition of 225mW of input pump power and at 20℃,36mW of output signal power was obtained,and the conversion efficiency is 16.0%.Furthermore a tunable infrared(IR)output from 1503~1550nm was obtained by tuning the temperature of PPMgLN from 20℃ to 180℃.关键词：nonlinear optics;optical parametric oscillator(OPO);periodically poled MgO:LiNbO3 crystal(PPMgLN);temperature tunable;quasi-phase matched114|78|1更新时间：2020-08-11
- 摘要：In recent years,the lots of novel effects of the quantum dots systems have attracted more and more physicists.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.Kandemir and Altanhan used the Lee-Low-Pines transformation to calculate the polaronic effects for an electron confined in a parabolic quantum dot.Zhu and Gu investigated the ground states and self-energy of the weak-coupling polaron in a parabolic quantum dot by using the second order Rayleigh-Sch rdinger perturbation theory.Li and Zhu investigated the strong-coupling polaron in a parabolic quantum dot by the Landau-Pekar variational treatment.It is shown that both the polaron binding energy and the average number of virtual phonons around the electron decrease with increasing the effective confinement length.Other investigations indicate that the bound interaction of the Coulomb potential plays an important role on the property of optical polaron.Es-shai et al.investigated the impurity bound polaron in a cubic quantum dot using the variational approach.Melnikov et al.applied the adiabatic variational method to calculate the polaron energy shift in a spherical quantum dot.Satori et al.attained the binding energy of a bound polaron to shallow donor impurity in spherical quantum dot using a vatiational approach within the effective mass approximation.One of this paper's authors achieved the vibration frequency and the average number of phonons of the strong-coupling bound magnetopolaron in a parabolic quantum dot by using the linear combination operator and unitary transformation methods.In the present paper,by using the variational method of Pekar type,we have studied both the ground state energy and the excited state energy of strong coupling bound polaron in parabolic quantum dot.The polaron energies in both the ground state and the excited state,the average number of virtual phonons around the electron were calculated.Their dependence on the effective confinement strength and the Coulomb potential was depicted.关键词：parabolic quantum dot;strong coupling;bound polaron;effective confinement strength97|80|0更新时间：2020-08-11
- 摘要：The properties of the excited state of the weak-and strong-coupling polaron in a parabolic quantum dot were studied by using the Huybrechts' linear combination operator and the unitary transformation method.The first internal excited state energy,the excitation energy and the resonance frequency of both the strong-and weak-coupling polaron in a parabolic quantum dot are derived respectively.First,we have investigated the properties of the excited state energy,the excitation energy and the resonance frequency of the weak-coupling polaron in a parabolic quantum dot.The relation of both the excited state energy with the effective confinement length of the quantum dot and the electron-phonons coupling strength and the excitation energy and the resonance frequency with the effective confinement length of the quantum dot.The results show that,the excited state energy will increase strongly with decreasing the effective confinement length of the quantum dot,and will increase with decreasing the electron-phonon coupling strength,and the excitation energy and the resonance frequency increase with decreasing the effective confinement length of the quantum dot.Second,the properties of the vibrational frequency,the excited state energy,the excitation energy and the resonance frequency of the strong-coupling polaron in a parabolic quantum dot are studied.The relation of these quantities with the effective confinement length of the quantum dot,and the electron-phonon coupling strength is discussed.The results show that,the internal excited state energy,the excitation energy and the resonance frequency will increase strongly with decreasing the effective confinement length of the quantum dot,and increase with decreasing the electron-phonon coupling strength,and the vibrational frequency increase with decreasing the effective confinement length and increase with increasing the electron-phonons coupling strength.关键词：parabolic quantum dot;strong-and weak-coupling;polaron;first internal excited state energy96|84|1更新时间：2020-08-11
- 摘要：Recently,with the quick development of nanofabrication technology to material,the physical cha-racteristics of low dimensional material have aroused great interest.The electron energy spectrum of such quantum dot is fully quantized.Such systems are of great interest in fundamental studies,as well as in practical application for microelectronic devices.Electron-phonon interaction,which plays an important role in electronic and optical properties of polar crystalline materials in three dimensions,will have pronounced effects in low-dimensional systems as well.The properties of polaron in quantum dot have been studied by many theoretical and experiment methods.Zhu and Gu studied the ground state and self-energy of the weak-coupling polaron in a quantum dot by using the second order Rayleigh-Sch rdinger perturbation theory.Using the Fock approximation of Matz and Burkey,Lepine and Bruneau discussed the effect of an anisotropic confinement on the ground state energy of a polaron in a parabolic quantum dot.Mukhopadhyay and Chatterjee investigated the polaronic corrections to the first excited state energy of an electron in a parabolic quantum dot using a canonical transformation method based on the L.L.P.G formation.Li and Zhu investigated the strong coupling polaron in a parabolic quantum dot by the Landau-Pekar variational treatment.It is shown that both the polaron binding energy and the average number of virtual phonons around the electron decrease with increasing the effective confinement length.The results indicate that the polaronic effects are more pronounced in quantum dots than those in two-dimensional and three-dimensional cases.With the use of variational approach,the effects of the bulk-LO phonon on the impurity binding energy in a GaAs quantum dot are studied by Es-sbai et al.Upon using a curvilinear coordinates system,Cantele et al.calculated the effective mass for a particle confined in an ellipsoidal quantum dot.Xie proposed a procedure to calculate the polaron effect of D- centers in quantum dots with a parabolic laternal confining potential by using the method of few-body physics.The properties of the polaron in a parabolic quantum dot are investigated by using a linear combination operator method by the present author and co-workers.However,so far research of the polaron in a quantum dot only was restricted to the approximation and calculation where the interaction between phonons of different wave vectors in the recoil process is neglected.The ground state energy of the polaron in parabolic quantum dot is derived by using a linear combination operator and perturbation methods.Considering interaction between phonons of different wave vectors in the recoil process,the influence on the ground state energy of polaron in quantum dot is discussed.Numerical calculations shown that the ground state energy of polaron in quantum dot will increase strongly with decreasing the effective confinement length and ground state energy will decrease with increasing the electron-LO phonon coupling strength.When l0＜1.4,the interaction between phonons can not be ignored in a parabolic quantum dot.关键词：parabolic quantum dot;polaron;interaction between phonons;ground state energy114|98|0更新时间：2020-08-11
- 摘要：A new kind of rare earth(RE)complex Tb(o-MBA)3phen was synthesized,and was used as an emitting material in electroluminescence devices.The material was doped into poly N-vinylcarbazole(PVK)as the emitting layer,which is made by spin coating.Three kinds of devices were fabricated with the structures:(A)ITO/PVK:Tb(o-MBA)3phen/LiF/Al;(B)ITO/PVK:Tb(o-MBA)3phen/BCP/Alq3/LiF/Al,(C)ITO/BCP/PVK:Tb(o-MBA)3phen/Alq3/LiF/Al.Bright green emission could be obtained from Device A and Device C.Photoluminescence(PL)and electroluminescence(EL)mechanisms of this material were investi-gated.There is an overlap between the PL spectrum of PVK and the excitation spectrum of the terbium complex,so there should be F rster energy transfer process between them.The excitation spectrum of Tb(o-MBA)3phen doped PVK system is alike with the excitation spectrum of PVK,yet it is different with that of Tb(o-MBA)3phen.So the emission of Tb(o-MBA)3phen should partly come from the excitation of PVK.While in the OLED based on Tb(o-MBA)3phen,the emission mainly come from the direct recombination of electron and hole.Bright green emission was obtained from the optimized multi-layer Device C and the highest EL brightness reached 180cd/m2 at the voltage of 17V.关键词：rare earth commplex;electroluminescence;exciton109|102|3更新时间：2020-08-11
- 摘要：A new blue-green light-emitting iridium(Ⅲ) bis(1-phenylpyridine)(1,2,4-triazole pyridine)complex was synthesized by the reaction of 1-phenylpyridine,1,2,4-triazole pyridine and iridium trichloride hydrate,which expanded the choice range of blue-light iridium complexes effectively.Most of multilayer phosphorescent devices which have been reported before were fabricated by high vacuum thermal evaporation.In this paper,polyvinylcarbazole(PVK)was used as polymer host by comparing the spectra overlap degree of photoluminescent(PL)emission spectrum of the host polymer(PVK and polyfluorene)and the absorption spectra of the iridium complex.Single-layer polymer blends structures are advantageous because they can be fabricated by solution processing at room temperature.Different concentration of iridium complex guest was doped into PVK host.PL spectra in solid film state weren't the same as those in solution state.Energy transfer from host to guest in solution state wasn't completely comparing with that in solid film state.Because F rster and Dexter energy transfer could be happened at the same time in solid film state.While in solution state,the distance of intermolecule is becoming farther,Dexter energy transfer couldn't be happened.With the increase of doping concentration,the intensity of PL emission peak of complex increased gradually.The structure of the complex was characterized by elemental analysis,1HNMR,and liquid-mass spectroscopy.The UV-Vis spectrum,photoluminescence spectrum and photoluminescence efficiency were investigated.Electroluminescence(EL)device was fabricated when the complex guest of 2% was doped into polymer host PVK.The UV-Vis spectrum showed the absorption peaks below 350nm are attributed to the spin-allowed single state 1π-π* transition of cyclometalated ligands.The complex also gives rise to a strong photoluminescence at 470 nm at room temperature under photo excitation.Compared to the photoluminescence spectrum,a red-shifted of emission was observed from the electroluminescence spectrum.This maybe resulted from the congregation of small-molecule guest or the formation of excimer.The reason of red-shift of EL spectra is in progress.关键词：phosphorescent material;iridium complex;PLED101|54|0更新时间：2020-08-11
- 摘要：It is known that Cu is necessary and no-replacable for ZnS powder ACEL.For this reason,the stability of Cu and its pattern in ZnS particle is the most important for maintenance of luminescence.Cu+ possesses a strong thermo-diffusion with diffusivity of about 10-9cm2/s in ZnS.At 900℃,ZnS particle of 7~10μm can be activated by Cu+ diffusion in few minutes completely.CuxS is a fast-ion conductor emerging very strong Cu+ migration in electric field.Because of high conductivity of CuxS,CuxS conductive line in ZnS grain is on the equipotential.The different equipotential surfaces from that of CuxS line are distributed making a detour around the CuxS line,not across the CuxS line and compressed near both ends of CuxS line.The most of current through the ZnS grain passed the CuxS line because the direction of current must be vertical to the equipotential surfaces.So that,the density of current in the CuxS line is not even,being the largest on the center,and weakening from the center to the ends gradually.关键词：luminescence;ZnS phosphors;Cu+ migration;aging94|74|1更新时间：2020-08-11
- 摘要：A series of phosphor of M2SiO4:Re(M=Mg,Ca,Ba;Re= Ce3+,Tb3+)were synthesized and studied.The excitation spectra measurement showed that M2SiO4(M=Mg,Ca,Ba)had high energy absorption in the excitation spectra centered at 147nm and 172nm.The excitation spectra of M2SiO4:Tb3+(M=Mg,Ca,Ba)consist of two broad bands:one is in the range from 130 to 200nm and the other is from 200 to 250nm.The former is assigned to the host absorption,the latter is attributed to the absorption of the Tb3+.Photoluminescence measurements indicated that M2SiO4:Re(M=Mg,Ca,Ba;Re=Ce3+,Tb3+)phosphor exhibits green emission under VUV excitation.However as Ce3+ doped in the samples,the absorption band decreases evidently in VUV.关键词：rare earth;VUV excitation;phosphor122|31|1更新时间：2020-08-11
- 摘要：Eu3+-doped Gd2Mo3O9 was prepared by solid-state reaction route using Na2CO3 as flux and characterized by powder X-ray diffraction.According to X-ray diffraction,this material is belongs to tetragonal system.The effects of flux content and sintering temperature on the luminescent properties were investigated by emission and excitation spectra.The results showed that flux content and sintering temperature have impact effects on the luminescent properties,the optimized flux content and the best sintering temperature is 3% and 800℃,respectively.The excitation and emission spectra also show that this phosphor can be effectively excited by C-T band(280nm),ultraviolet light 395nm and blue light 465nm.The wavelengths at 395nm and 465nm are nicely fitting in with the widely applied emission wavelengths of ultraviolet or blue LED chips.Integrated emission intensity of Gd2Mo3O9:Eu is 2 times stronger than that of Y2O2S:Eu3+ under 395nm excitation.The Eu3+ doped Gd2Mo3O9 phosphor may be a better phosphor candidate for solid-state lighting applications.关键词：Gd2Mo3O9：Eu;red emitting phosphors;white LED;Na2CO3 flux reagent131|63|23更新时间：2020-08-11
- 摘要：In the past few years,ceramic laser materials have emerged with many advantages,such as lower cost fabrication,high melting temperature and large size samples more easily to be manufactured,as compared to crystals and glasses.There has been remarkable interest in rare-earth-doped ferroelectric ceramics which are suitable material for novel integrated-optic devices formed by a combination of lasers/amplifier with electro-optic(EO)and nonlinear-optic waveguide components.Recently,a new highly transparent,electro-optic ceramic material,Er3+ and Er3+/Yb3+ ions doped Pb1-xLaxZryTi1-yO3(PLZT),have been fabricated,which have exceptionally high electro-optic(EO)effect.The up-conversion luminescence of Er3+ and Er3+/Yb3+ ions doped PLZT for active electro-optical applications has been investigated.The green light of 540 nm and 566 nm can be observed in Er3+ doped PLZT.Moreover,their intensity gets stronger along with concentration of Er3+.In Er3+/Yb3+ co-doped PLZT,besides the green light of 540 nm and 566 nm,a relatively weak red light of 668 nm can also be observed.To all sample,the nonlinear curves fitting to the relationship between up-conversion intensity and excitation intensity were made,which were concluded that both red emission and green emission were the absorption process of double-photon.And again the character of up-conversion luminescence was discussed using the Raman spectra of PLZT.The theory and experimentation both show Er3+ and Er3+/Yb3+ ions doped PLZT,based on its large electro-optical effect,have a prospect to be applied for electro-optic Q-switched double-function up-conversion laser device.关键词：up-conversion luminescence;electro-optic ceramic PLZT;rare earth ions of Er3+ and Yb3+116|52|1更新时间：2020-08-11
- 摘要：Hydrotalcite-like compounds(HTlcs),which are formulated as [M1-x2+Mx3+(OH)2]An/xn-·mH2O have received increase interest owing to their particular properties such as infrared absorption.The properties are derived from their special layers structure,which are made of metal cations(M2+ and M3+)of similar ionic radii and coordinated by six oxygen atoms forming M2+/M3+(OH)6 octahedra.Luminescent materials containing rare-earth ions have been special interest for their sharp and intense emission bands based on f→f transitions of rare-earth ions.In fact,europium compounds are the most widely used due to their efficient red-emitting luminescence,so doping of europium ions into HTlcs makes it possible to combine the optical properties of molecular compounds with the mechanical and chemical stability of a solid matrix.Therefore,it suggests that there is a new method of designing dual-functional materials.In order to getting dual-functional materials with red luminescence and selectivity IR adsorption properties,we studied the HTlcs compound containing Eu3+ ions.The samples of Mg-Al-Eu-hydrotalcite-like compounds(MgAlEuCO3-HTlcs)were prepared by co-precipitation and through hydrothermal treatment.Results of XRD showed that the pure MgAlEuCO3-HTlcs were obtained from solution of magnesium,aluminium and europium nitrates,n(Mg2+):n(Al3+)=3,n(Eu3+):[n(Al3+)+n(Eu3+)]=5%～50%,by co-precipitation with a mixture of sodium carbonate and hydroxide at a fixed pH value of 10±0.1,and hydrothermal treating at 100℃ for 8h.The MgAlEuCO3-HTlcs crystallinity decreases with increasing Eu3+ dosage in the synthesis mixture,and the value of d110 of MgAlEuCO3-HTlcs is more larger in XRD at one time.Three intense IR bands of FT-IR spectra at 600～900cm-1,1250～1350cm-1 and 3420～3480cm-1 are argument with MOH(M=Mg,Al,Eu),CO3 and OH stretching vibrations,respectively.Under excitation by 399 nm,there are three sharp emissions peaked at 594,620 and 700 nm in emission spectrum of MgAlEuCO3-HTlcs,which belong to the 5D0→7FJ(J=1,2,4)transition of Eu3+ ion.Besides,the intensity of luminescence changed with the increasing of Eu/Al molar ratio.All of results revealed that a few Al3+ ions in layers of HTlcs were replaced by Eu3+ ions in our samples.It was found that the MgAlEuCO3-HTlcs compound is a novel dual-function material with selectivity absorbing infrared wavelength and red luminescence.关键词：europium;hydrotalcite-like compounds;IR absorption;luminescence102|79|2更新时间：2020-08-11
- 摘要：The samples of CaTiO3:Pr3+,Zn2TiO4:Pr3+,Ca0.7Zn0.3-xCdxTiO3:Pr3+(x=0.01,0.03,0.05,0.07,0.09,0.1)were synthesized by the conventional solid state reaction.XRD measurements confirmed that the prepared CaTiO3:Pr3+ and the Zn2TiO4:Pr3+ belonged to orthorhombic structure according with JCPDS Card(42-423)and cubic structure according with JCPDS Card(25-1164),respectively.The XRD profile of the Ca0.7Zn0.3-xCdxTiO3:Pr3+(x=0.01,0.03,0.05,0.07,0.09,0.1)showed the two phases which were CaTiO3:Pr3+ and Zn2TiO4:Pr3+ respectively.The excitation spectra of CaTiO3:Pr3+ were located at 150~350 nm,and composed of two continuous zone:the first one originated about 230 nm,the second one originated around 321 nm.Both hailed from the absorption of the transition O(2p)→Ti(3d).The excitation spectra of Zn2TiO4:Pr3+ around 324 nm differed from that of CaTiO3:Pr3+,and the excitation spectra of Ca0.7Zn0.3TiO3:Pr3+ showed the characteristics of both the CaTiO3:Pr3+ and the Zn2TiO4:Pr3+,which indicated the effect of substitution or partial substitution of Zn for Ca on the luminescent properties of CaTiO3:Pr3+.In contrast with the Ca0.7Zn0.3TiO3:Pr3+,the excitation spectra of Ca0.7Zn0.3-xCdxTiO3:Pr3+(x=0.01,0.03,0.05,0.07,0.09,0.1)were intensified at the narrow peak about 324 nm,which indicated the effect of partial substitution Cd for Zn on the luminescent properties of Ca0.7Zn0.3TiO3:Pr3+.The all emission spectra have a sharp peak of Pr3+ at about 612 nm characterizing the transition of 1D2→3H4 of Pr3+.The intensity of emission peaks of Ca0.7Zn0.3-xCdxTiO3:Pr3+(x=0.01,0.03,0.05,0.07,0.09,0.1)was increased with increasing of x value when the x was in the range of 0.01～0.07.关键词：calcium titanate;Cd;luminescence108|84|4更新时间：2020-08-11
- 摘要：REAl3(BO3)4 was well known as good laser materials,but its fluorescent nano-powders have not been well studied.A series of fluorescent nano-powders Gd1-xEuxAl3(BO3)4 has been synthesized by solid reactions.Raw materials Al2O3,H3BO3,Gd2O3,Eu2O3 were well mixed and baked at 400℃/2h first,then 750℃/4 h,and 1150℃/8h the last.After being well grinded the fluorescent powders of Gd1-xEuxAl3(BO3)4 has been synthesized.The samples were characterized by XRD,and the microcrystal diameter of the samples were calculated to be within 100 nanometer by XRD diagram.Their luminescent properties of the fluorescent powders were measured by the RF540 fluorescence spectrometer(Japan)with “suspending powder method” with glycerin as the dispersing medium.The samples of GdAl3(BO3)4 gave the emission spectrum at 310 nm when excited by the light of 280 nm,and the spectrum of dispersing medium glycerin did not disturb the spectrum of GdAl3(BO3)4.The samples of Gd1-xEuxAl3(BO3)4 almost had the same emission spectrum of Eu3+ no matter they were excited by 390 nm or by 280 nm.The strongest emission of Eu3+ was 5D0→7F2 transition.So there was no symmetry position in the crystal structure of Gd1-xEuxAl3(BO3)4 by the rule of fluorescent probe.The emission spectrum of 5D0→7F2 was higher excited by 280 nm than that excited by 390 nm.It was the evidence of the energy transfer between Gd3+-Eu3+.The experiment results show that fluorescent powders with nanometer microcrystals of Gd1-xEuxAl3(BO3)4 can be synthesized by solid reactions.GdAl3(BO3)4:Eu3+ gives 618 nm emission spectrum as the transition 5D0→7F2,and there was no symmetry position in the crystal structure of Gd1-xEuxAl3(BO3)4.The experiment results show that there was energy transfer between Gd3+-Eu3+.Because of its fine properties of fluorescence and its stability of material,the fluorescent nano-powders of Gd1-xEuxAl3(BO3)4 may possess great value for being further studied and used.关键词：Gd1-xEuxAl3(BO3)4 synthesis;suspending powder method;emission spectrum;excitation spectrum;energy transfer104|67|0更新时间：2020-08-11
- 摘要：Lead-activated BaSi2O5(BaSi2O5:Pb,BSP)is used as the long wavelength UV phosphor in suntanning lamps,as well as speciality lamps for diazo-printing reprography,lithography,insect traps,photoche-mical and curing processes.A well-known problem with the use of this material is that its radiance maintenance is poor.That is,lamps employing the BaSi2O5:Pb phosphor exhibit a large decrease in radiant output over time.Presently,the stabilization of the light output of tanning lamps is achieved by the application of an Al2O3 coating onto the surface of BSP particles.This measure requires a gas phase process,since the wet chemical precipitation of Al(OH)3 has to be performed at an acidic pH,i.e.in an environment which is hazardous to BSP.It is an object to provide a solution based method for BSP that can be performed at a high pH and is thus harmless to the phosphor,and further object to improve the lamp maintenance of BSP phosphor.The method involves adding an amount of a silicate phosphor to a salt solution containing a cation,such as Ba2+,stirring the solution for a time sufficient to cause the cation to attach to the phosphor surface,separating the cation-treated phosphor from the solution,and annealing the phosphor at a temperature for a time sufficient to increase radiance maintenance of the cation-treated phosphor.The surface morphology and the surface component of cation-treated BSP phosphor were investigated by means of SEM and XPS,respectively.The luminescent performances of the lamps using the cation-treated phosphor and untreated phosphor were tested.The results demonstrate that cation-treated phosphor shows a decrease in the ratio of Si/Ba surface atoms,and lighting test indicates that lamp employing the cation-treated phosphor has a significant improvement in radiance maintenance.关键词：phosphor;surface treatment;degradation101|53|2更新时间：2020-08-11
- 摘要：Using the first-principles calculation with 64 and 128 atom supercells the geometric and electronic structures of InN quantum dots(QDs)embedded in wurtzite GaN were simulated.After optimizing the stress and total energies,electronic structures of the stable systems were further calculated.The electronic densities of states show distinguishing quantum-confine-effects along different axes.Moreover,the curves of energy band edge appear in InN QDs.Compared with the typical band-edge shape of quantum well under the polarization that leads to the separation of electrons and holes in space,we found that the separation problem could be eliminated due to the curves of energy band edge in QDs,which is favourable for enhancement of the transition probability of the electrons and holes.关键词：quantum dots;quantum confine effects;density of states117|161|3更新时间：2020-08-11
- 摘要：Glasses doped with nanosized Ⅱ-Ⅵ semiconductor particles such as CdS or metals like Ag have attracted much attention because of their large non-linear optical properties.Meanwhile,semiconductor/metal hybrid particles have also been suggested as a scheme to provide substantial further enhancement of both the optical non-linear and the figure of merit(χ3/absorption).Glasses doped with large number of silver particles(~1% additional in mass fraction)were prepared by a glass precipitation method and heat-treatment process after UV irradiation.Their structure was studied by X-ray diffraction(XRD)and high-resolution scan electron microscopy(HRSEM).Optical properties were researched by absorption spectra and PL spectra.HRSEM pictures of CdS/Ag clearly indicated that all crystallites are uniformly distributed in the glass matrix with 1μm in radius and consist of clusters of small particles with size of 0.5μm.The XRD results showed that samples with UV irradiation and thermal treatment exhibit diffraction peaks of silver and CdS,samples with thermal treatment only exhibit peaks of CdS particles,while samples without thermal treatment were nearly amorphous type.The absorption spectra of CdS/Ag particles show a typical surface plasmon resonance feature at 420 nm and a peak at 600 nm which was attributed to the CdS,while samples with CdS particles only exhibit a peak at around 480 nm,and samples without thermal treatment have a peak at 320 nm which may be caused by slight crystallization of the CdS nanocrystallites during quenching.The PL peak of the glasses doped with CdS consists of three peaks.However,in CdS/Ag doped glass,the CdS PL peak was vanished.In order to explain this phenomenon,a resonant energy transfer mechanism was proposed.The formation mechanism of Ag particles by UV irradiation was discussed.The results indicated that the electron on the semiconductor surface can reduce silver ions upon the irradiation of the glass and lead to formation of silver particles,accompanying with the capture of the holes by the surface defects.关键词：UV irradiation;CdS/Ag;optical properties129|68|1更新时间：2020-08-11
- 摘要：InGaN/GaN quantum well exhibits a series of unusual optical properties.However,the physics of quantum well on the micro scale is subjected to large uncertainties.Little is known on the discontinuities of energy band structure and local states on the atomic level in the case of different In atoms distribution in the InxGa1-xN layers caused by In compositional fluctuation and phase separation,which intensively alters the optical and electronic pro-perties.Using the efficient and accurate total energy and molecular-dynamics package VASP which is based on the density functional method,we performed the first principles calculations on InGaN/GaN quantum wells.The calcu-lated results exhibit discrete bands around the conduction band minimum and the valence band maximum that vary with the In atom distributions.Moreover,the local states with the discrete bands are likely to appear the quantum confined Stark effect in the InGaN/GaN interface enhanced by the polarization field in the crystal.The control and further understanding of those micro characteristics may lead to the improved performance of InGaN QWs.关键词：InGaN;quantum well;VASP;energy band structure97|54|2更新时间：2020-08-11
- 摘要：Self-organized semiconductor structures with reduced dimensionality are currently attracting strong interest due to the potential device advantages.The size,distribution and density of quantum dots(QDs)influence on the optical and electrical properties of QDs device.The QDs with bimodal size distribution have been investigated widely due to its some distinctive features compared to the single Gaussian distribution QDs.Thus,it is very important to understand the effects of the growth parameters and mechanisms on the growth of bimodal size distribution QDs.The InAs QDs are grown on the(100)semi-insulating GaAs wafers in Riber 32 compact 21 solid source molecular beam epitaxy(MBE)system equipped with a valved cracker cell for arsenic and reflection high-energy electron diffraction(RHEED)for in situ monitoring of the growth process.Growth temperature is calibrated by infrared pyrometer.First,a GaAs buffer layer with thickness of 100 nm was deposited,and then a single layer of quantum dots was grown by depositing InAs with thickness of 2.7ML at different growth temperature(520℃ or 480℃),finaly a 15 nm GaAs cap layer was deposited.The RHEED pattern shows a transformation from streaky to well developed diffraction spots,typical of a three dimensional(3D)growth mode.The same structures without cap layer were grown for atomic force microscopy(AFM)topographic investigation.The measurements of the distribution and topographic images of uncapped dots were taken ex situ by Nanoscope Ⅲ AFM.The photoluminescence(PL)measurements were performed in closed-cycle N2 cryostat under the excitation of 514.5 nm line of an Ar+ laser.Its luminescence spectra were detected with a Fourier transform infrared spectrometer operating with an InGaAs photodetector.Effect of growth temperature on the evolution of bimodal QDs is investigated by combining AFM and PL.The QDs density is significantly reduced from 8.0×1010cm-2 to 5.0×109cm-2 as the growth temperature increases from 480℃ to 520℃,while the average QDs diameter and height becomes larger.The formation of bimodal QDs depends on the growth temperature:at 480℃ growth temperature,large QDs result from the small QDs coalition;at 520℃ growth temperature,indium desorption and InAs segregation result in the formation of small QDs.关键词：quantum dot;molecular beam epitaxy;photoluminescence;atomic force microscopy103|124|0更新时间：2020-08-11
- 摘要：The study of the temperature dependence of photoluminescence(PL)in self-assembled quantum dots(QDs)is essentially important for the realization of room temperature efficient photonic devices.The temperature dependence of photoluminescence in self-assembled QDs will be directly determined by the temperature dependence of carrier dynamics process in self-assembled QDs.As the temperature increases,the carriers will thermal escape into the wetting layer(WL)from the ground states of an ensemble of QDs with difference sizes and then some of them will be recaptured by other QDs,i.e.carrier will transfer between the ensemble of QDs with difference sizes when the temperature increases.The temperature dependence of carrier dynamics process in self-assembled QDs was simulated with the steady-state rate equation model of carrier dynamics.The model takes into account the temperature depen-dence of the energy band gap of QDs material.The PL spectra of self-assembled QDs at difference temperatures and the temperature dependence of integrated PL intensity,FWHM and peak position were obtained.The results show that the calculated temperature dependence of integrated PL intensity,FWHM and peak position is consistent with the experimental data reported before.The agreement between experimental data and model simulations suggests the description of the carrier dynamics process in self-assembled QDs by the steady-state rate equation model taking into account the temperature dependence of the energy band gap of self-assembled QDs material is viable.关键词：self-assembled quantum dots(QDs);photoluminescence;thermal escape;retrapping100|92|0更新时间：2020-08-11
- 摘要：GaN/InGaN light emitting diodes(LEDs)grown on sapphire substrates have current transport along the lateral direction.This often results in non-uniform current spreading,which leads to the non-uni-formity of luminescence and the reduction of lifetime.Therefore,proper mesa structure should be designed to improve current spreading.The characteristics of the GaN/InGaN LED have been examined from the view point of uniform current spreading and low series resistance.A steady-state current field model is employed to describe the current spreading of GaN based LED.Finite element method is used to simulate the current distribution of different types of LEDs in three dimensions.The series resistance of the LED is derived from the calculated current spreading.Standards to quantitatively evaluate the uniformity of current spreading are presented.By quantitatively comparing the series resistance and current spreading of LEDs with different mesa structures,we find that that the LED with the interdigitated mesa structure has the lowest series resistance under the process conditions of our lab.Parameters of the interdigitated mesa structure are further optimized based on our model to achieve the smallest series resistance.Two types of LEDs,denoted as Sample A and Sample B,are prepared with a chip size of 1mm×1mm.Sample A is fabricated using the optimized interdigitated electrode pattern as described above,while Sample B is fabricated using a ring electrode pattern without optimization for comparison.By measuring the I-V curve,the values of series resistance of the three samples are derived,which are 1.6Ω and 3.6Ω for Sample A and Sample B,respectively.The resistance of the former one is only 44.4% of the latter one,which is consistent with the calculated results based on our model.The reduction in resistance will lead to the improvement of the efficiency of LEDs.关键词：GaN-based LED;current spreading;series resistance;finite element method;mesa structure85|167|3更新时间：2020-08-11
- 摘要：The silicon-based materials,such as silicon nitride,silicon carbide and silicon oxide etc,have been studied extensively both for their optical and electric characteristics.Especially,the luminescent be-haviors have been attracting much attention in order to develop Si-based light emitting diodes and even laser.Recently,strong blue to red light emission have been observed in amorphous silicon nitride in some reports.Also the photoluminescence and electroluminescence of silicon oxide have been realized and the silicon-based optical gain was also demonstrated.In this report,the optical characteristics of a series of amorphous silicon carbide films with different ratio of carbon to silicon have been studied.The ratio is controlled by changing the gas ratio(R)of methane to silane from 2 to 15,which resulted in different bonding configurations,microstructures and different optical characteristics,such as luminescence behavior and refraction index.Photoluminescence excited by Ar+ 488 nm laser and by the continuous wavelength xenon lamp,FTIR and Raman scattering have been used to analyze and explain the character and the micro structure of the films.It was found that the strong luminescence can be observed for samples deposited at R<10.The luminescence peak and intensity was obviously changed after step by step steady-furnace-annealing from 400℃ to 800℃.The Gaussian-simulation indicated that two luminescence bands appear in all the spectra for the samples annealed at the different temperatures and their intensities were changed with the annealing temperature.This illustrated the transformation of the microstructure of the films at different annealing temperatures.The luminescence can be related to the radiative recombination of the electron-holes in the localized tail states which are excited in the extended states.The blue light emission can be found for samples deposited at R>10 and the luminescence intensity was enhanced after post-annealing under UV light excitation.Based on the optical properties of a-SiC films,all a-SiC film based optical microcavities were designed and prepared by controlling the thickness and composition of a-SiC films.The resonant enhancement of luminescence band at 650 nm was achieved and the luminescence band was significantly narrowed.The modulation effect due to the existence of micro-cavity was demonstrated.The present results revealed the possibility to realize the solid state microcavity light emitting diodes.关键词：amorphous silicon-carbide;photoluminescence;microstructures;optical microcavity118|154|2更新时间：2020-08-11
- 摘要：Efficient blue-LED was successfully manufactured by Nichia Company of Japan,in 1996,then it made that the solid-state lighting went into the field of white light illumination.Subsequently the white-LED came true,it was made from InGaN blue-LED and YAG:Ce3+ phosphor,hereafter the internationally scientific research institute paid great attention to it.And it was also arranged in the “863” Program in China.When the organic dyes were doped into silicon dioxide(SiO2),it can be synthesized organic-inorganic composite luminescence material,which had both the excellent luminous property of the organic luminescent molecule and the stability of the inorganic material for the heat,chemistry and mechanism.So this kind of composite phosphor was considered as the ideal fluorescence transforming material.Composite phosphor is easy to product and the production cost is very low,and there is not any pollution in the fabrication procession.Because of all the advantages,the people were further to be favor of this method.Because the Sol-gel Gateway has many advantages compare to the traditional method of solid phase reaction.It can provide a simple,economic and effective method to produce high quality material.Many chemical reactions can be finished in a low temperature and the reaction procession is easy to be controlled.The doping distribution is even in the composite material.The organic-inorganic composite phosphor was synthesized with the Sol-gel Gateway in this paper,which based on the raw material of TEOS and organic fluorescent dye.The procession of fabrication was discussed and some of the properties were researched,including the influence of the doping concentration of the organic fluorescent dyes,the ratio of H2O to TEOS and the pH value on the reaction time and the material performance.Using the testing method of PL spectra,XRD and TEM,the properties of composite phosphor were identified,including spectrum,structure,granularity and appea-rance.It can be seen from the TEM image of the phosphor that the powder is transparent in nanometer size.The spectra of the phosphor at the different doping concentration indicates that the excitation wavelength is 450 nm and the emission wavelength is 520 nm,the excitation spectra peak is not changed with the doping concentration but the intensity of fluorescence is inflected by it,and the best doping concentration is 5×10-4mol/L.The excitation band is wide so that it satisfies the requirement of the white-LED.关键词：photoluminescence;sol-gel gateway;organic-inorganic composite phosphor122|153|2更新时间：2020-08-11
- 摘要：The relationship between minority carrier life and morphology with luminescent properties in porous silicon was studied.The surface morphology of the porous silicon(PS)samples was observed by the field emission scanning electron microscopy(FESEM)and the atom force microscopy(AFM)and microwave photo-conductance decay(μ-PCD)technique was first used to measure the minority carrier lifetime of PS.The results show that the porosity of porous silicon increased with the increase of etched time,which lead to the decrease of minority carrier life and the increase of luminescent efficiency of porous silicon.When the minority carrier life of PS decreases,the irradiative centers on surface of PS increase,which lead to decreasing of photoluminescence(PL)efficiency.Furthermore the results of μ-PCD technique showed the un-uniformity of minority carrier life of PS,which lead to the un-uniformity of PL efficiencies on different location of PS surface.This result proved that the formation of PS is depending on current density and back illumination strength.The results of the PL spectra and the Fourier transform infrared(FTIR)spectra illuminated that the emission came from the formation of surface confined emitters that related to the defects in silicon dioxides and the hydrogen atoms on surface of PS samples played as a key role to dissipate the irradiative centers and increase the PL efficiency.In addition,the result of morphology observation by atomic force microscopy exhibited that the surface of porous silicon became smooth gradually with increase of etched time,which may be related to the chemical etching during the electrochemical etching process.关键词：porous silicon;minority carrier life;surface morphology;photoluminescence95|126|0更新时间：2020-08-11
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