最新刊期
卷 22 ， 期 1 ， 2001
- 摘要：Random frequency modulations exist in many systems, such as magnetic system and glasses at low temperature, dye-solution. In magnetic systems, spin flips of doped ions or nuclei in the host lattice can cause the magnetic fluctuations at the impurity site, and hence the stochastic change of the transition frequency of the impurity ions. It is the main source of doped ions’ optical dephasing at low temperature. Because the interactions have various time scales and strengths, they can lead to a time-dependent broadening spectral line (heterogeneous line), the process is socalled spectral diffusion. Several theoretical methods have been used to explain this phenomenon. They all divided the interactions into only two time scales, the fast one results from spin flipping of the bulk nuclei, and the slow one comes from the contributions of the nearby nuclear spins in a frozen core. However, to describe the complete dynamic process in practical systems, these two time scales are obviously not enough. In addition, spectral diffusion is a typical frequency domain process, but almost no theoretical work started from the pure frequency domain point.In this paper, the spectral diffusion in paramagnetic ions doped system at high field, in which has the modulation-frequency-dependent jump rates, is studied in both frequency and time domains. In general, the spectral diffusion goes as [1-exp(-WTw)]x. Without frozen core, the values of x are 1/2 and 1 for frequency and time domains, respectively. Considering frozen core effect, the spectral diffusions are slow down by the factor of (ωeff/ω0)2, where ω0 is the frequency characterized frozen core, and ωeff are ωmax and H∞ for frequency and time domains, respectively. When the frozen core is large enough, the spectral diffusions in two domains tend to have the same form as x≈0.22.关键词：spectral diffusion;random frequency modulation;paramagnetic ion112|86|0更新时间：2020-08-11
- 摘要：The fluorescence properties of Cr4+ doped inorganic glasses are of current interest, besides its potential use as a lumophore in tunable near-infrared media, Cr4+ is also useful as a spectroscopic probe to infer information about the local environment in amorphous solids. In glass hosts,Cr4+ ions are very likely surrounded by an oxygen tetrahedren. The Cr4+ emission is determined by the strength of the crystal field, for low crystal field, 3T2 is the lowest excited state, the emission is a broadband, while for high crystal field, 1E is the lowest excited state, the emission is a sharp line. Cr4+ ions in MgCaBa-aluminate glass were found to be the case of intermediate crystal field, where the state mixing approach should be applied to analyze the emission lineshape. The room temperature fluorescence spectrum includes a sharp line at 1.18μm and a broadband in the region 1.1～1.4μm, which assigned to 1E→3A2 and 3T2→3A2 transition respectively. In this paper, the ASE(Amplified Spontaneous Emission) method is presented to study the optical gain, this technique could be described as below:A cylindrical lens is used to focuses laser to an equally line,then make the beam get through a length adjustable slit,detected the fluorescence from the vertical side of the sample,the emission intensity for varied excited length is:I(l)=IsA/g[exp (gl)-1] Where Is is the spontaneous emission rate per unit volume, A is the cross sectional area of the excited volume, g is the optical gain coefficient.Fitting the experiment result to the above equation, the optical gain coefficient of Cr4+:MgCaBa aluminate glass are BE=(0.7±0.04)mm-1 and BT=(0.05±0.005)mm-1 at 1.18μm and 1.24μm respectively.关键词：Cr4+ ions;near-infrared emission;optical gain120|89|0更新时间：2020-08-11
- 摘要：The self sum frequency mixing (self-SFM) process is recently recognized as a new way of obtaining blue lasers,that is,summing the fundamental laser generated by a LD and remaining LD light by means of a single nonlinear laser crystal.This kind of scheme can achieve both laser action and nonlinear conversion in one crystal,which results in more compact,robust and manageable devices. A theoretical model for describing the self-SFM laser generation is developed,in which spatial distributions of the pump and fundamental lasers with arbitrary beam waists are fully taken into account.The analysis can be simplified by using the average approximation.The output power of the self-SFM laser is related to many physical parameters such as crystal length,doped ion concentration,pump waist,cavity mode size,walk-off angle,pump power,absorption coefficient at the pump wavelength,phase mismatch and effective nonlinear coefficient.Hence it is necessary to reach a compromise among the above parameters in order to optimize the self-SFM laser output.The model is applied to the self-SFM laser generated by two kinds of crystals of current interest,NYAB and Nd:GdCOB.Their self-SFM laser output properties are theoretically discussed,predicted or verified.The calculated results are compared with the experiments,which shows the validity of our model. Based on the analysis of applying the model to NYAB and Nd:GdCOB,some useful information can be summarized on improving the output power of the self-SFM laser,that is,large effective nonlinear coefficient,small walk-off angle,small internal loss,small phase mismatch,suitable beam waists(pump and fundamental),appropriate crystal length and ion concentration. The model is not limited to self-SFM lasers and may be applied to general analysis of the laser generation with Gaussian beams,for instance,fundamental oscillation,SFD lasers,intracavity-frequency-doubling lasers and microchip lasers.Particularly,for microchip lasers,the model can be further simplified by assuming that the pump waist and cavity mode size are constant in the gain medium.98|105|0更新时间：2020-08-11
- 摘要：The aim of the work is to study the local struture of KCdF3 doped with Cr3+ and Li+ ions by means of the quantitative relationship between the ZFS parameter and the crystal structure.The present work suggests that the tetragonal crystal field of Cr3+ ion in KCdF3:Cr3+,Li+ crystals comes from following two origins:(1) The equivalent charge caused by the charge compensation in the [001]-axis direction. (2) The lattice distortions of the nearest-neighbor fluorine coordination.In fact,when Cr3+ and Li+ ions doped into KCdF3 crystals, Cr3+ ions replace divalent Cd2+ ions. Owing to the difference in charge, mass, and radius between Cr3+ and Cd2+ ion, the lattice distortion occurs to the local structure of Cr3+-Li+ centres in KCdF3 crystals. Due to the charge compensation, a Cd2+ ion on [001]-axis will be replace by Li+ ion. Because of these, the local structure distorts and local point symmetry around Cr3+ changes from Oh to C4v. According to the idea,the relationship between the zero field splitting D and crystal structure for Cr3+ in KCdF3:Cr3+,Li+ crystals has been established by means of the superposition model and third order perturbation theory.The EPR zero field splitting parameter D has been investigated,taking account of both effect of lattice distortion and the equivalent charge.The calculated result(D=-0.06203cm-1) is in excellent agreement with experimental result(D=-0.06212(5)cm-1).Meanwhile,the results,the F- ion moves toward the central Cr3+ ion by ΔR1=0.00268nm,ΔR21=0.001nm,ΔR3=0.00165nm,are obtained.关键词：KCdF3：Cr3+;Li+;zero-field splitting;charge compensation;local structure90|101|0更新时间：2020-08-11
- 摘要：In the past,the blue component of three colors lamp,BaMgAl10O17:Eu2+,was prepared by high temperature solid state method.This paper focuses on the rapid preparation of the phosphors BaMgAl10O17:Eu2+,RE(RE=rare earth) by combustion method in air at 600℃ and on the effect of rare earth ions on the properties of the blue phosphor BaMgAl10O17:Eu2+.The XRD analysis shows that the d values and relative intensity(I/I0)values of the phosphors BaMgAl10O17:Eu2+,RE accord with the standard values in JCPDS card.The structure of the phosphors belongs to hexagonal symmetry.This argues that the combustion synthesis of the blue phosphors BaMgAl10O17:Eu2+,RE is feasible and effective.In addition,compared to the high temperature solid state reaction,this combustion procedure has advantages of producing the phosphors with smaller particle size,uinform distribution,higher specific surface area and highly efficient luminescence,and synthesis of the phosphors activated by low value state rare earth ions such as Eu2+ has no use for hydrogen or carbon power as reduction atmosphere.The excitation and emission spectra and the phosphorescence decay curves of the phosphors are measured and analyzed.The excitation and emission spectra are identical with that of the phosphors prepared by solid state reaction.The effect of rare earth ions on Eu2+ luminescence is as follows.Only the luminescence of Ce3+,Gd3+,Tb3+ are observed in the host BaMgAl10O17 among all three-value state rare earth ions.When co-doped with Eu2+ and three-value state rare earth ions,the luminescence of other three-value state rare earth ions are not found in the host except Ce3+,which has very weak luminescence.This is due to the strong absorption of Eu2+ restraining the excitation and emission of Ce3+,Gd3+,Tb3+ ions.In addition,the long lasting phosphorescence in those phosphors co-activated by Eu2+ and Pr3+、Nd3+、Dy3+、Ho3+、Er3+ are observed for the first time.But the position of phosphorescence of Eu2+ is 489nm,red shift accounts to 39nm compared to the normal spectral peak position of Eu2+ in BaMgAl10O17:Eu2+.Further studies on the mechanism of phosphorescence and emission position shift are in progress.关键词：aluminate phosphors;combustion synthesis;long lasting phosphorescence85|91|9更新时间：2020-08-11
- 摘要：With the development of matter science and technology, the properties of polaron in crystals have been of considerable interest. Many investigators studied the polaron problem by means of various theoretical methods. There are many references and remarkable works. In most polar crystals there is one mode of the longitudinal optical(LO) phonon. The properties of crystals have been studied by a great variety of techniques in the case of the crystals having only one LO phonon branch. However, a large number of polar crystals, with several atoms per unit cell, have more than one LO phonon branch. For example, a large number of perovskites and quaternary compound semiconductor crystals have more than two LO phonon branches. In recent years, the polaron problem with many LO phonon branches has been investigated. Hu and Xiao et al. have discussed the properties of the polaron and exciton in polyatomic polar crystals using a linear-combination operator method. Frequency of the lattice vibration in ionic crystals bears a relation to the wave vector. In general case,when treating the interaction between the longitudinal optical vibration in ionic crystals and charged particle, the frequency of the phonon is always thought to be constant, and the variation of this frequency with the wave vector is neglected. Gu discussed the influence of the dispersion of LO phonon on the properties of polaron under considering the dispersion of LO phonon for the first time. In this paper, the dispersion of the longitudinal optical phonons is considered in a sine approximation. The ground state energy, effective mass and self-energy of a polaron in polyatomic crystals are calculated using perturbation method.关键词：sine dispersion phonon field;polyatomic crystals;polaron94|104|0更新时间：2020-08-11
- 摘要：In the early 1970s,Ibach carried out low-energy electron diffraction experiments on ZnO and other semiconductor surface.Sak,Evans and Mills studied theoretically the surface polaron in polar crystals, the Hamiltonian of the electron and surface phonon interaction was derived. Gu et al. discussed the ideal surface polaron and the weak,intermediate-coupling polaron in a semi-infinite polar crystal. Mills indicated that when electron moves in the surface vicinity of the crystals,the electron and surface optical phonon interaction produces a polarization cloud around the electron,whereas because of the electron surface acoustic phonon coupling the electron have been trapped at the surface vicinity motion.Theoretical results show that the surface layer of crystals may be regarded as pure 2D crystals if the distance from the surface is smaller than the radius of polarons.The effect of bulk phonons can be neglected,while surface acoustic and surface optical phonons are taken into account in the surface layer. Ueba discussed the properties of the electron,which is a interaction with both the surface optical and acoustic phonons in the surface phonon field. Toyozawa studied the quasi-particle, the acoustic deformation potential (ADP) polaron,formed by the interaction of electrons with acoustic lattice vibration using the concept of the deformation potential.Recently Zhao Cui-lan et al. investigated the properties of surface polaron of interaction with the deformation potential.From the point of view of confined electron,studying electron via the deformation potential interaction with acoustic phonon is more significant.The properties of surface polaron in polar crystals,which is a weak-coupling with surface optical and surface acoustic phonons,was studied. In the paper,the renormalization mass of the surface polaron is derived using Tokuda’s improved linear-combination operator and the Lagrange multiplier and the variational method. Two limiting cases are discussed.关键词：surface polaron;weak-coupling;renormalization mass96|116|0更新时间：2020-08-11
- 摘要：With the development of the solid science and experimental technology,the properties of the surface polaron in crystals have been of considerable interest.Many investigators studied the properties of the effective mass of the surface polaron by the method of a perturbation,a strong-coupling variational wavefunction,a linear-combination operator and a Green-function et al.However,the research of these methods only was restricted to the case of crystals having only one mode of the longitudinal optical(LO)phonon.However,a large number of polar crystals,with several atoms per unit cell,have more than one LO phonon branch.For example,in cuprite such as CuO2 there are two LO phonon modes and a large number of perovskites (SrTiO3,BaTiO3,LiNbO3…)have more than two modes.In recent years the polaron problem with many LO phonon branches has been studied.The properties of polaron in polyatomic polar crystals are discussed by the method of a linear combination operator and a simple unitary transformation by one of the authors.However,the influences of the electron interaction with both bulk longitudinal optical phonons and surface optical(SO) phonons on the properties of the surface polaron in polyatomic crystals has not been investigated so far.In this paper,the effective mass of the surface polaron in polyatomic semi-infinite crystals, weak coupling with both bulk longitudinal optical and surface optical phonons,are studied using a linear combination operator and Lagrange multiplier method.关键词：polyatomic semi-infinite crystals;surface polaron;effective mass101|88|1更新时间：2020-08-11
- 摘要：The properties of polaron of crystals influence the optical properties of the crystals very remarkably. With the development of magneto-optical technology, the properties of the polaron for polar crystals in magnetic field have been of considerable interest. Zorkani et al. calculated the ground state energy of bound magnetopolaron using variational method. Employing Haga’s perturbation method, Hu et al. derived an effective Hamiltonian for the interface magnetopolaron in polar crystals to zero temperature. Kandemir et al. discussed the ground-state and first-excited-state energy of two-dimensional large magnetopolaron by using recently introduced squeezed Landau states. The effective mass of magnetopolaron in polar crystals was investigated by means of a linear-combination operator and a perturbation method by one of the authors. Most polar crystals are diatomic and cubic and their crystal structure belongs to NaCl, CsCl or ZnS type. In these crystals there is one mode of the longitudinal optical (LO) phonon. The properties of crystals have been studied by a great variety of techniques,in the case of crystals having only one LO phonon branch. However,a large number of polar crystals, with several atoms per unit cell, have more than one LO phonon branch. For example, in cuprite such as CuO2, there are two LO phonon modes. Si2,GaAs1-xPx and a large number of perovskites (SrTiO3,BaTiO3,LiNbO3, ets.) have more than two modes. In recent years, the polaron problem with many LO phonon branches has been investigated. The properties of the polaron in polyatomic polar crystals are studied using a linear-combination operator method by one of the authors. However, the magnetopolaron in polyatomic polar crystals has not been investigated so far. Recently, Wei and co-workers studied the properties of strong-coupling surface magnetopolaron in polyatomic polar crystals. In this paper, the properties of the bulk polaron for polyatomic polar crystals in magnetic field are studied. The ground state energy of a strong-and weak-coupling bulk polaron in polyatomic polar crystals are derived by the method of a linear-combination operator.关键词：polyatomic polar crystals;bulk polaron;linear combination operator;ground state energy140|84|0更新时间：2020-08-11
- 摘要：The aim of this paper is to explore the effect of coupling between the transverse motion and the longitudinal motion of an electron on the resonant tunneling characteristics in a multibarrier heterostructure.A method developed in a previous paper is extended to derive the related formula for the transmission coefficients depending on both the transverse wave number and the longitudinal kinetic energy of an incident electron.A static field is introduced to discuss the influence of the bias voltage on the transmission coefficients,and also to investigate the effect of the coupling between the components of the motion of an electron in the directions of parallel and perpendicular to the interface.A numerical calculation is carried out for the rectangular and parabolic-barrier heterostructures consisting of CdSe/Zn1-xCdxSe.In the case of without a bias voltage,it is found that the coupling effect not only leads to a move of the resonant peaks toward the low-energy region,but also causes the broadening of the resonant peaks and the reduction of the peak-to-valley ratio in the transmission spectrum.The influence of the transverse motion of an electron on the higher-lying resonant states for the resonant tunneling is more remarkable than that on the lower-lying resonant states.When the bias voltage is non-zero,a same conclusion is obtained:the resonant peaks also move towards the high-energy region.In addition, when the transverse wave number is constant,the resonant peaks also move towards the low-energy region.Furthermore,the resonant peaks in the lower region will disappear as the bias voltage increases.It is shown that the coupling between components of the motion of the electron in direction parallel and perpendicular to the interface is significant for the resonant-tunneling.关键词：resonant tunneling;coupling effect;transmission coefficient91|98|2更新时间：2020-08-11
- 摘要：Study on anti Stokes Fluorescent Cooling develops rapidly in recent years.But,there are many problems in its groundwork and applications.So,a period of time is needed to put this high tech in practicality. Even though, all researchers in this field insist that laser cooling tech will play an important part in some field in future.The cryocoolers based on anti-Stokes fluorescent emission will be mini volume,lighter weight,electromagnetic radiation free,non-vibration and non-noise,beacuse of light driving only in this technique.The abroad researchers studied much in laser cooling,because of its great potential applications in military,space,integrated optics,micro-electronics,iatrology,and etc.The breakthrough in laser cooling as a basically technique must result in application of many high teches which require special temperature conditions and must promote their fields developing forward. In this paper, we introduce the first generation laser cryocooler disigned by Los Alamos and forecast the future development of fluorescent cryocooler and discuss the gist of its design.Some consideration on design of coil form,cooling to integrated circuit and single molecule-photon crycooler are proposed.关键词：laser cooling;anti-Stokes fluorescent cooling;fluorescent cryocooler131|141|1更新时间：2020-08-11
- 摘要：The J-O theory used to calculate optical properties of Er3+ in oxide-fluoride glass,the oscillator strengths,transition probabilities,branching ratios and the lifetimes were obtained.The absorption spectra,emission spectra,and excitation spectra were measured. We present a preparation method of fluoride-oxide glass (MFT) containing TeO2,PbF2,AlF3,BaF2,NaF,doped with Er3+ ions.The impurity concentration of Er3+ in this sample is 2mol%.Based on the J-O theory the optical transition properties were calculated using the absorption spectra data.The J-O parameter Ω2,Ω4,Ω6 are 1.637E-20,0.225E-0,0.480E-20,respectively.The oscillator strength,transition probabilities,the branching ratios and radioactive transition lifetimes were obtained.The calculated results are analogous with experimental observation.The excitation spectra were measured at 550 and 660nm.The emission spectra were measured under different excitation wavelength related to the excitation spectra.关键词：Er3+;oxide-fluoride glass;J-O theory93|111|4更新时间：2020-08-11
- 摘要：Upconversion of erbium, ytterbium co-doped glass were studied. The luminescence spectra in 800nm near-infrared region were analyzed, which is caused by three kinds of transitions. Except for the ordinary 4F9/2→4I15/2 transition,there are another two transitions:2H11/2→4I13/2, 4S3/2→4I13/2. Effects of Er3+ concentration on the three transitions are also researched. With 966nm-laser diode as pumping source,we measured the excitation and emission spectra of six bulk glasses with different Er3+ concentrations with F111AI model fluorescence-meter.Except green and yellow upconversion luminescence(coresponding to the transitions 2H11/2→4I15/2, 2S3/2→4I15/2 and 4F9/2→4I15/2),there is a luminescence band in 780～850nm in the near-infrared region.The peak at 830nm is apparent and higher with lower concentration.With the Er3+ concentration increasing,the peak at 830nm disappears while the peak at 800nm becomes apparent. According to the excitation spectra of the samples and the energy levels of Er3+,we think that the near-infrared upconversion luminescence band consists of three kinds of transitions:4S3/2→4I13/2 (central wavelength:842nm), 2H11/2→4I13/2 (central wavelength:820nm) and 4I9/2→4I15/2 (central wavelength:800nm).When Er3+ concentration is low,the populations in 2H11, 4S3/2 levels are more,most of the populations on these two levels will transit to the 4I15/2 and emit green light,another part of the populations will transit to 4I13/2 level and 830nm light emits. When Er3+ concentration is higher, because of the increase of the excite-state-absorption(ESA) and non-radiation rate to 4I9/2 level as well as the possibility of cross-relaxation from 2H11/2, 4S3/2 to 4I9/2 (2H11/2, 4S3/2→4I9/2, 4I15/2→4I13/2),the population in 4I9/2 increases while the populations in 2H11/2 and 4S3/2 levels decrease,so that the transition 4I9/2→4I15/2 (800nm) becomes stronger,surpassing the light intensity from 2H11/2 and 4S3/2 to 4I13/2.关键词：erbium;upconversion luminescence109|84|3更新时间：2020-08-11
- 摘要：Fluoride glasses and crystals with good transparency,low phonon energy and large rare earth ion solubility are promising hosts for optically active ions,which have attracted great attention because of the possibilities of realizing blue or green solid state lasers.However,they are difficult to fiberize due to low chemical and mechanical stability.Most oxide glasses are chemically and mechanically stable although they have higher phonon energy comparing with those of the fluoride host.Recently,oxyfluoride glass-ceramics were developed by growing the fluoride micro-crystals containing rare earth ions into oxide host.As a result,oxyfluoride glass-ceramics have low phonon energy just like fluoride and its good chemical and mechanical stability just like oxide glass. The relation between upconversion intensity and pumped power is quadratic (or cubic) in the process of up-conversion luminescence corresponding to double-photon(or three photon)process.But in our experiment,green up-conversion fluorescent intensity of Er3+ in Er3+-Yb3+ codoped SiO2-Al2O3-PbF2-CdF2 transparent glass-ceramics does not show a quadratic dependence versus the pumped laser intensity although green up-conversion luminescence is corresponding to a double-photon process.And the green up-conversion fluorescent intensity saturated gradually with the pumped laser power. Relation between Er3+ up-converted luminescent intensity and pump power in Er3+-Yb3+-codoped material are studied by transfer function theory.Er3+ up-converted luminescent process in oxyfluoride glass-ceramics is discussed and it’s found that the non-quadratic relation between green up-conversion intensity and pump power is caused by strong cross-relaxation process of rare earth ions.Methods of increasing Er3+ up-converted luminescent intensity in oxyfluoride glass-ceramics are suggested.119|192|2更新时间：2020-08-11
- 摘要：The search for new high-efficient phosphors is of great importance for plasma display panel (PDP) as the rapid development of this new technology. The PDP red phosphor used is still insufficient to meet the demand of full-color PDP because of the low color saturation. New red phosphor with high color saturation and high luminescent efficiency is urgently needed. YP1-xVxO4:Eu3+, with good color saturation (main emission at 619nm), is well known as a high-efficient red phosphor under UV excitation. In this paper, YP1-xVxO4:Eu3+ was prepared carefully at high temperature in solid state reaction. The luminescence of YP1-xVxO4:Eu3+ was studied under VUV/VU excitation. YP1-xVxO4:Eu3+ was identified as forming solid solution based on the Vegard′s rule. The strongest emission in YPO4:Eu3+ was observed at 593nm and in YP1-xVxO4:Eu3+ (0.2≤x≤1) at 619nm. Additionally, the blue emission from VO43-, except the red emission of Eu3+, can be observed when the V5+ concentration is lower than 0.3. This blue emission will be quenched by Eu3+ emission when the V5+ concentration equal to or larger than 0.3. In the UV excitation spectra of YP1-xVxO4:Eu3+ (0.2≤x≤1), the absorption band of (P1-xVx)O43- and Eu3+ charge transfer band were observed overlapping at UV region and shift to a longer wavelength with increasing V5+ concentration. In the VUV excitation spectra of YP1-xVxO4:Eu3+,a very narrow band was observed locating at 153nm in YPO4:Eu3+ while a broad band in the same region were observed in other systems with varying x value. The narrow band is assumed to the absorption of PO43- while these broad bands are to P1-xVxO43- anion. Moreover, a band around 200 nm was also observed similar to the absorption of Y2O3, which is attributed to Y-O absorption. The luminescence efficiency of YP1-xVxO4:Eu3+ (0.2≤x≤1) increases with the increasing of P5+ concentration, consistent with the increasing ionic character of P1-xVxO43- anion. This seems to imply that host with stronger ionic character is more favorable for host sensitization on activator. An optimized constituent,YP0.7V0.3O4:Eu3+, which has 30% higher luminescent intensity than that of commercial Y2O3:Eu for PDP under 147nm excitation and 12.5% higher under 172nm excitation and a better red color saturation, will be a new potential red phosphor for plasma display panel (PDP).关键词：YP0.7V0.3O4：Eu3+;VUV excitation spectra;PDP phosphor87|132|13更新时间：2020-08-11
- 摘要：It is found that there is emission stimulated by infrared radiation for some aluminate phosphors doped by Eu2+,such as SrAl2O4:Eu(green),SrAl14O25:Eu(blue-green) and CaAl2O4:Eu(blue). Under the excitation of UV light,this kind of aluminate phosphors can give photoluminescence (PL).The PL spectrum of SrAl14O25:Eu peaked at about 265～280nm,under the excitation of 254nm.The stimulated emission spectrum is the same as PL spectrum for these Eu2+ doped aluminate phosphors. Since the existence of deep electron traps in the phosphors, the excitation energy can be stored after the excitation of UV or sunlight,then the infrared radiation can induce the energy release by means of stimulated emission. The stimulated emission from the aluminate phosphor has a long decay time up to a few 10min.This phenomenon can be used to detect the infrared laser emission.关键词：stimulated emission;aluminates phosphors;detection of infrared laser98|134|0更新时间：2020-08-11
- 摘要：A polythiophen derivative was synthesized as an light-emitting layer of LED,and its electroluminescent properties have been investigated under low and superlow temperature.The energy gap is about 2.04eV,the peak of photoluminescent spectrum is at 630nm and the emitting intensity is higher for this compound.The diode began to emit at 18V when it was in liquid nitrogen,ITO as a positive electrode,the metals as negative one (the ratio of Mg and In is 10 to 1).The intensity increases rapidly with increasing voltage and it is clear enough to be visible when the applied voltage is higher than 20V.The diode also possesses better rectification because there was no electric current when a reverse voltage was applied.It gives a red emission peaked at about 687nm.Although the diode can give red emission at room temperature in vacuum and the wavelength is still 687nm,and the applied voltage is much lower than that in liquid nitrogen,it begins to light when the voltage is 6V. The above results reveal that the plolythiophen appears some good electroluminescent properties either at room temperature or at low temperature.The studies are significant for studing the electroluminescent properties of organic high polymers,especially at low temperature.关键词：polythiophene derivative;electroluminescence;light-emitting diode98|121|1更新时间：2020-08-11
- 摘要：The photoluminescence(PL) of nanorods SiC was demonstrated in this paper. The excited light source is Ar+(514nm)laser,the apparatus is Renishaw MKE-1000 Raman spectrometer. The nanorod means diameter is 2～4nm, and length is 40～60nm. The PL peak of nanorods SiC is 654nm, its intensity is the highest SiC PL spectrum in previous experiments. Because the nanorods SiC is a superstrong scattering media, at the threshold for photon localization, the diffusion modes of light interfere strongly and are converted into a continuous spectrum of localized cavity modes in the extended medium, in which emitting light may be self-organized into a coherent states. The striking effect is that the threshold for photon localization is very low. The output light is Raman random laser.关键词：nanorods SiC;low-dimension semiconductor;photoluminescence;quantum effect125|173|0更新时间：2020-08-11
- 摘要：The discovery of room-temperature photoluminescence from silicon-based materials has stimulated the renewed interest in the field of silicon-based optoelectronics. In the past few years, much effort has been directed in searching for better silicon-based light-emitting materials. Through doping oxygen in silicon, considerable light emission in the variant range has been successfully achieved. But very few studies have been carried out on the photoluminescence property of silicon material codoped by oxygen and nitrogen. In the paper, several strong luminescence bands and peaks from oxygen and nitrogen codoped silicon thin film were reported. The thin films were deposited onto silicon wafers by plasma enhanced chemical vapor deposition (PECVD) using SiH4, H2, O2 and NH3 at 300℃ with thickness about 500nm. Changing the flow rate of discharge gases during deposition modulated the thin film composition. The depositing chamber was evacuated to 10-4 Pa, depositing pressure was 80Pa, and discharge r f. power density was 0.15W/cm2. The photoluminescence spectra of thin films were measured using RF 5301 photoluminescence spectrometer at room temperature. The results of X-ray diffraction measurement show that the structure of thin films is amorphous. The thin film composition varies with changing the flow rate of discharge gases during deposition, and assumes different photoluminescence properties. In the SiOx:H thin film, strong photoluminescence at about 300～570nm was observed at room temperature. The central position shifts towards lower energy with the increase of oxygen content. When the partial pressure of O2 during deposition is increased to 15Pa, blue light band containing distinguishable photoluminescence peaks is achieved. Photoluminescence spectrum of SiOxNy:H thin film is composed of bands and distinguishable peaks. The photoluminescence bands are localized at 250～400nm and 500～700nm, and central position depends on the flow rate of H2 during deposition. When the flow rate of H2 increases, central position shifts towards higher energy. The distinguishable photoluminescence peaks centered at about 370nm and 730nm. They strengthen with the increase of N content in the thin film. Above experimental results show that photoluminescence from thin film is related to O and N impurities. It is suggested that photoluminescence possibly originates from light-emitting centers related to O and N impurity levels.关键词：amorphous Si:H thin film;O and N impurity level;photoluminescence91|98|0更新时间：2020-08-11
- 摘要：The growth of unintentionally doped GaN films was performed by organometallic vapor phase epitaxy on (0001) sapphire substrates using a home-made vertical reactor at atmospheric pressure.These GaN films were grown using trimethylgallium(TMGa) and triethylgallium(TEGa) as Ga precursors under different growth condition.The blue-ammonia was used as N source.The mixed gases of hydrogen and nitrogen were used as the carrier gases.The sapphire substrate was heated at 1100℃ for 10 minutes before the GaN growth.Then a thin buffer layer with thickness of about 15nm was grown at 520℃ and recrystallized at 1060℃ for 6 minutes.The GaN films were grown at 1060℃ and its thickness was about 1μm.The morphorlogical,crystalline,electrical and optical characteristics of GaN films were measured by metalloscope observation,X-ray double crystal diffraction measurement,Van der Pauw Hall method and PL spectra measurement at room temperature,respectively.The metalloscope observation results indicated that the epilayer of sample A was uncontinuous.So we inferred that the nucleation sites were not enough when using TEGa as buffer’s Ga source.By analyzing the experiment results and growth condition,it is suggested that TEGa is not very suitable to be used as buffer layer’s Ga precursor,but it is good precursor as the epilayer’s sources in growth of GaN films.The carrier gas ratio[H2]/[N2]influenced the epilayer quality greatly.When using TEGa as epilayer’s Ga source and TMGa as buffer’s Ga source,we obtained GaN single crystal films with RT background carrier concentration of 4.5×1017 cm-3 and the mobility of 198cm2/V·s.The PL measurement indicated that the blue luminescence can be suppressed using TEGa as the epilayer’s Ga precursor.关键词：GaN;MOCVD;TEGa;TMGa155|167|0更新时间：2020-08-11
- 摘要：Polymers that contain nonlinear optical moieties are considered to be most promising for the development of electro-optic devices. There are a number of different ways to make polymer channel waveguides, such as photobleaching, reactive ion etching, and laser ablation. The photobleaching technique for forming polymer channel waveguides in a planar geometry offers compatibility with existing electronic processing technologies. Because UV light can induce a series of chemical reactions when a polymer film is exposed under it, and can also make a remarkable decrease for both thickness and refractive indexes of polymer film. Using these characteristics, we fabricated ridge polymer waveguides with DANS-PMMA side-chain polymer films. The fabricating process is as follows. The DANS-PMMA is dissolved in 1,2-Dich loroethane. Then the solution is filtered through 0.5μm sieve and spread onto fused silica substrate by spin coating. After 24 hours curing at 60℃. Al layer is evaporated onto the DANS-PMMA film and a 6μm-wide of Al strip is constructed by photolithography. Then the sample is exposed to UV light through Al strip mask for 10 minutes. The measured light power on the sample surface is 40mW/cm2, and sample temperature is 80℃. After photobleaching, a 6μm-wide of DANS polymer strip waveguide is formed when Al mask is removed. The microscope view show that the surface and side-wall of this waveguide are very smooth. This kind of waveguide is similar in shape to that of normal ridge waveguide, but it’s refractive index distribution is similar to that of rectangular waveguide. Therefore ridge polymer waveguide can supply better restrict for transmitting light. In practical devices, the ridge polymer waveguide is sandwiched between upper and lower cladding layers. The eigenvalue functions and propagation constants are deduced for this kind of waveguide using the analysis method of slab waveguide. The normalized curves are plotted for guide index b as a function of normalized frequency V for Enmy and Enmx mode.关键词：ridge waveguide;polymer;eigenvalue functions119|124|0更新时间：2020-08-11
- 摘要：Erbium doped fiber amplifier was pumped by Al-free 980nm InGaAs/InGaAsP/InGaP high power quantum well laser. At pump power of 20mW, the gain is 33dB, the maximum gain coefficient is 6.7dB/mW and the saturated output power is 6dBm. The gain is as a function of fiber length and pump powers, it is also as a function of output powers.关键词：erbium doped fiber;amplifier;gain95|130|1更新时间：2020-08-11
- 摘要：Cr3+ and Nd3+have been widely used as an optical activator in solid state luminescent and laser materials. A lot of works on Nd3+and Cr3+ co-doped crystals and glasses have been made, in which the sensitive ion Cr3+ can increase the absorption, pump efficiency and quantum efficiency to Nd3+ due to the superimposition of emission of Cr3+ and absorption of Nd3+. Crystals have high quantum efficiency, but cannot be synthesized into large size materials. Glasses can not meet the demands of applications because of low quantum efficiency. Glass-ceramics are glass-crystallite composites where the crystallites are developed by heat treatment of already formed glass. The activator doped glass-ceramics have the merits and characteristics of glass, crystals and ceramics, and are capable of cheap fabrication of large dimensions of devices. In this paper, the transparent glass-ceramics B2O3-Al2O3-SiO3 codoped by Cr3+ and Nd3+ were prepared by heating in one step process according to the principle of phase segregation. The main crystalline phase checked by XRD is a mullite solid solution. Absorption, emission spectra and lifetime of samples were measured. The distribution of sites for Cr3+ and Nd3+in samples and the spectroscopic characteristics were analyzed and discussed by contrasting co-doped samples with singly-doped ones. The absorption spectra of co-doped sample is approximately equal to the superimposition of absorption of singly-doped Cr3+ on that of singly-doped Nd3+sample. The intensity of emission at 700nm for the co-doped sample by 647nm excitation is only 65% of that of singly-doped Cr3+, and the intensity of emission at 700nm and 775nm by 568nm excitation are 87% and 70% respectively. The Nd3+lifetime observed at 1060nm increased by 45% due to radiation trapping in the co-doped sample compared to the sample containing Nd3+only. It is shown that there are radiative and nonradiative energy transfers from Cr3+ to Nd3+. The Cr3+ ions almost universally favor octahedral coordination in crystalline phase, and Nd3+would concentrate in the residual glass phase. The distribution of Cr3+ ions will affect on the spectroscopic characteristics of Cr and Nd doped glass-ceramics. From our experiments and studies, the authors came to realize that a stronger process of radiative and nonradiative energy transfer from Cr3+ to Nd3+was observed in the transparent B2O3 Al2O3 Si2 glass-ceramics co-doped with Cr3+ and Nd3+.The distribution of Cr3+ sites characterized by crystal field parameter Dq affected on the energy transfer process, where low field Cr3+ sites have a higher energy transfer efficiency than that under high field.关键词：Cr3+ and Nd3+doping;emission spectra;energy transfer;glass-ceramics95|93|0更新时间：2020-08-11
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