最新刊期
卷 30 ， 期 3 ， 2009
- 摘要：A new selective Zn2+ fluorescent sensor, N'-(2-hydroxybenzylidene)-4-(2-hydroxy-benzylidene-amino) benzohydrazide (HHB), was synthesized. With the harbored 2-hydroxybenzylidene group, HHB exhibits an emission band centered at 475 nm with high quantum yield (f= 0.59) upon the addition of zinc ions. It features excellent fluorescence enhancement and provides favorable sensitivity for Zn2+ detection under the biological pH window of 6.8~7.7, and high selectivity for Zn2+ over biologically relevant alkali metals, alkaline earth metals and some of the first row transition metal. It works through the metal-assisted hydrolysis mechanism, and the hydrolysis residue sensor HB, salicylaldehyde-4-aminobenzoylhydrazone, was also investigated for comparison.关键词：fluorescent sensor;Zn2+;hydrolysis;selectivity96|70|1更新时间：2020-08-12
- 摘要：The long afterglow photoluminescence materials have the particular properties storing light energy and glowing slowly at dark circumstances. That is, the materials can absorb the visible lights, store the energy, and then release the energy as the visible lights. Particularly, alkaline earth aluminates doped with rare earth ions have excellent luminescence properties such as high brightness, no radiation, safety, long duration, and environmental capability,resulting in its wide applications in many fields.In this paper,Sr1-xBaxAl2O4 : Eu2+ ,Dy3+(x=0,0.2,0.4,0.6,0.8,1.0)phosphors were synthesized in a reducing atmosphere by high temperature solid state method at 1 350 ℃ with H3BO3 as flux. The phosphors were characterized by X-ray diffraction(XRD). The results showed that crystal structure of the phosphors is the monoclinic phase of SrAl2O4 when x＜0.4 and the hexagonal phase of the BaAl2O4 when x≥ 0.4. The lattice plane distances of the phosphors increase with the content of Ba2+, which could be explained that Ba2+ ion radius is bigger than that of Sr2+ ion. The crystal lattice expands with barium ion substitution for strontium ion. Photoluminescence experiments were carried out to study luminescence properties of the phosphors under the excitation of UV. The results showed that the peak of the emission spectra shifts from 515 nm to 494 nm with the x changing from 0 to 1.0. The blue shift phenomenon could be explained by the crystal field effect, which is affected by different coulomb attractive forces due to Ba2+ ion doping in the host lattice. Long afterglow properties were investigated by thermoluminescence. Thermoluminescence measurements showed that trap energy level of the SrAl2O4 crystal structure is deeper than that of BaAl2O4. The afterglow decay measuring showed that the phosphors of SrAl2O4 crystal structure have the more superior afterglow performance than that of BaAl2O4.关键词：solid state method;photoluminescence;strontium aluminate;long afterglow85|49|3更新时间：2020-08-12
- 摘要：Alkaline-earth metal aluminate phosphor CaAl12O19 : Eu,Mn was synthesized by solid reaction method. The structure, excitation and emission spectra of samples of phosphors were analyzed by XRD and F-4500, the influence of the calcination temperature and the concentration of Eu3+ on the luminescent performance of samples was observed.The influence mechanism of Eu3+ was studied. The results showed that the phosphors can be excited by the ultraviolet, near-ultraviolet, blue and green light below 550 nm, the emission peaks are at 590,615,645,657 nm, the peaks 590,615 nm are the characteristic emission of Eu3+, the another two peaks are the 2E-4A2 transition emission of Mn4+ . The experiments showed that the optimal calcination temperature and time are 1 550 ℃ and 4 h, respectively, the optimal mol fraction of Eu3+ is 0.11%.关键词：phosphor;aluminate;luminescent properties;luminescent properties of Mn4+131|28|7更新时间：2020-08-12
- 摘要：The binding energies of donor impurity states in quantum wells in the presence of an electric field were investigated by a variational method. The impurity-center as well as the bound electron couplings with both the longitudinal optical (LO) and interface optical (IO) phonons were taken into account in the calculation. The binding energies were obtained as the functions of impurity position, well width and electric field strength. The results for GaAs/Al0.3Ga0.7As quantum wells as an example were given and discussed. It was found that the correction due to electron-phonon interaction to the impurity state binding energies and the Stark shifts is quite significant.关键词：donor impurity state;electron-phonon interaction;quantum well;Stark effect103|77|0更新时间：2020-08-12
- 摘要：Because the complex structure of Quantum Ring, it is difficult to solve the Schrdinger equation, so it is uncertain to comfirm the energy levels and wave function. Many scholars have worked on this problem, but they have few papers on this problem. It is necessary to seek another method to solve this problem. The energy levels of a two dimensional quantum ring with an impurity in parabolic confinement under magnetic field is calculated by the B-spline functions. The dependency of the energy levels on the strength of magnetic field and ring radius is studied. We found that there is a minimum for each of the energy levels at certain ring radius. And the position of the minimum shifts to the direction of larger radius as the excited energy levels increasing.关键词：B-spline function;quantum ring;impurity;size effect95|142|0更新时间：2020-08-12
- 摘要：Spectroscopic ellipsometry(SE) was employed to characterize ZnO thin films prepared by pulsed laser deposition (PLD) on Si (100) substrates at various temperature of 400, 500, 600 and 700 ℃. The refractive indices (n) and extinction coefficients (k) of the ZnO films were calculated in the spectral range of 400~800 nm for each deposition temperature by fitting the ellipsometic parameters based on a three-layers dispersion with Cauchy model. It was found that the optical constants were significantly affected by the substrate temperature. Through analyzing the crystalline structures and surface morphologies of ZnO thin films grown at different substrate temperature by XRD and atomic force microscopy (AFM), respectively, the variation of the refractive index can be attributed to the changes of the packing density of the thin film. After comparing the results obtained at different grown temperature, it was suggested 600 ℃ might be the optimum deposition temperature for growing dense ZnO films with high optical and crystalline quality.关键词：spectroscopic ellipsometry;PLD;zinc oxide;optical constants119|117|0更新时间：2020-08-12
- 摘要：Tm3+/Yb3+-codoped transparent oxyfluoride glass and glass ceramics were prepared by melt-quenching and subsequently heat-treatment to forming the fluoride nanocrystals embedded among the oxide glassy matrix. The advantages of these materials are that the rare earth ions are incorporated selectively in the fluoride crystal phase with lower phonon energy after heat-treatment and the material remains transparent due to much smaller size of precipitated crystals than the wavelength of visible light. Intense blue upconversion luminescence was observed under 980 nm laser excitation. X-ray diffraction (XRD) and fluorescence spectra investigation reveal that fluoride nanocrystals are distributed homogeneously among the glassy matrix for the sample doped with Tm3+/Yb3+. Tm3+ is one of the most studied rare-earth ions for blue laser operation based on upconversion. One approach to improving the luminescent efficiency of Tm3+ is to co-doped with other rare-earth ions. The choice of host materials is also an important issue when it deals with improving the efficiency of the emission process. With the increasing Yb3+ concentration, blue upconversion emissions show different variable tendency in glass and glass ceramics co-doped with Tm3+/Yb3+. In this paper, different upconversion energy transfer processes were explained and reverse energy transfer pathway from Tm3+(3H4) to Yb3+(2F5/2) was influenced by crystal lattice field in glass and glass ceramics. In glass, the competition of positive and reverse energy transfer between Tm3+ and Yb3+ ions causes maximal blue upconversion emission at optimal Yb3+ concentration. The blue upconversion emission, however, increases with the increasing Yb3+ ion in glass ceramics.关键词：glass ceramics;upconversion luminescence;Tm3+/Yb3+;energy transfer112|200|0更新时间：2020-08-12
- 摘要：The variable-temperature photoluminescence spectra of strained InAsxP1-x/InP heterostructuer were experimentally determined in the temperature range 13~300 K. A theoretical calculation was presented that takes into account the temperature-induced variations in band gap and biaxial strain to explain the PL spectra. The results showed that strain which is induced by lattice mismatch between epitaxial layer and substrate removes the degeneracy between the light- and heavy-hole states at the top of the valence band, and with temperature under 100 K,the recombinations from the conduction band to the split valence bands are both observed in the photoluminescence spectra. As temperature is raised,it results in an increasingly larger light-hole population than that of heavy-hole due to thermalization, so when temperature is beyond 100 K only the recombination from the conduction band to the light-hole state can be observed.We also find that the energy of the recombination between the conduction band and the light-hole and heavy-hole state changes as a function of temperature.关键词：InAsxP1-x/InP;LP-MOCVD;stress;variable-temperature photoluminescence114|85|0更新时间：2020-08-12
- 摘要：AlN is a new type of direct wide bandgap Ⅲ-V nitride semiconductor material.Because the AlN possesses of many interesting physics characteristics,it has attracted huge attention on potential applications. In addition, AlN is a type of direct bandgap semiconductor material with a very wide direct bandgap of 6.2 eV, as solid-state light sources, which are in the process of profoundly changing the way that human generates light for general lighting applications. Solid-state light sources possess of two highly desirable features, which set them apart from most other light sources: (i) they have the potential to create light with essentially unit power efficiency and (ii) the properties of light can be controlled to a degree.In another actual application, AlN as a kind of high-efficiency ultraviolet solid-state light sources is greatly important material to develop short wavelength ultraviolet light-emitting diodes. Microelectronic fabrication technologies and the enviromental sciences both require light source with shorter emission wavelengths, such as the former to imporve resolution in photolithography and the latter for sensors that can instantaneously detect hazardous particles. Furthermore, ultraviolet solid-state light sources are also attracting attention for potential applications in high-density optical data storage, biomedical research, water and air purification, and sterilization.In recent years, the great importance of semiconductor material has been realized in the fabrication of the shoter emission wavelength light-emitting diodes, resulting in research on AlN thin film. At present, resear-chers have completed Si doped AlN n-type conduction with very strong conductivity. Lately, Nepal et al. made use of Zn doping to obtain p-type AlN.However, the efficiency of doping is quite low, the p-type AIN possesses of lower quantum energy, and the acceptor compositions need to be detected further.In this paper, we studied the efficiency of Zn and Cd as p-type doping in wurtzite AlN crystals. In the present study we performed the geometrical structure of Zn and Cd doped 32 atoms supercell of AlN, which is optimized by adopting the ultra-soft pseudopotential method of total-energy plan wave based on the destiny functional theory(DFT). Cell parameters of both undoped and doped cells were calculated theoretically. Binding energy, partial destiny of state and electron destiny differences of doped AlN crystals were calculated and discussed in detail. We focus our attention on whether the doping can provide enough holes in doped AlN crystals. The result of our calculation revealed the fact that both Cd and Zn atoms can provide a good deal of the state holes, which means that both of them are well p-type doping, nevertheless, comparing with Cd, Zn has a better solubility in AlN crystals, because Zn in AlN crystals can provide more the state of hole, which is propitious to come into being better p-type conduction. We prove that Zn is a better p-type doping ion than Cd.关键词：AlN;p-type doping;density functional theory;electronic structure105|308|9更新时间：2020-08-12
- 摘要：The laser emission around wavelength at 1.55 μm is located in the "eye-safe" region and plays an important role in the optical communication and remote sensing. However, Er3+-doped materials cannot be efficiently pumped by the InGaAs laser diodes because of the lower absorption of Er3+ at the wavelength of 976 nm. Generally, the solution is to add Yb3+ ion as a sensitizer to improve the pumping efficiency. So, in the Yb3+ and Er3+ co-doped materials, the pumping energy can be efficiently absorbed by Yb3+ and transferred to Er3+. In this paper, YAl3(BO3)4 crystals with different Yb3+ and Er3+ doping concentrations were grown by the flux method. The Yb3+ to Er3+ energy transfer in YAB crystals was investigated with the rate equation without considering the back energy transfer and up-conversion processes. The simple formulation for calcula-ting the energy transfer coefficients was derived according to the fluorescence lifetimes of Yb3+ ion. The energy transfer parameters were also calculated. The results showed that the energy transfer is very efficient in the YAB crystal and the energy transfer probabilities from Yb3+ to Er3+ increases with the increasing of Yb3+ concentrations. The energy transfer coefficients calculated by using experimental data are accordant with those calculated by theory, it means that the formulation is suitable for calculating the energy transfer coefficient in the high phonon energy materials. The energy transfer coefficients and critical interaction distance are comparable with or higher than those in other materials, which means that the energy transfer from Yb3+ to Er3+in YAB crystal can be more efficient. So, this host could be a good candidate for the 1.55 μm laser media.关键词：YAB crystal;rate equation;energy transfer102|213|1更新时间：2020-08-12
- 摘要：MgWO4 is a self-activated luminescent material, chemical and luminous properties are stable. It has high quantum efficiency and has been used as lamp phosphor for a long-term. MgWO4 is usually prepared by solid-phase method using high purity MgO or MgCO3 mixture with WO3, then sintered at about 1 200 ℃ for several hours. Solid-phase approach leads to unhomogeneous distribution of sample size, the particles easily reunion, and the particle size is difficult to control, but hydrothermal method can overcome these shortco-mings. In recent years, hydrothermal method has been used to synthesis some kinds of tungstate samples, such as BaWO4,NaLa(WO4)2, PbWO4 and so on, but to synthesis MgWO4,it has not been reported.Amberg and John.R synthesized pure MgWO4·H2O and MgWO4·2H2O by mild hydrothermal method, but without studying on their luminescent properties. This article reports about using hydrothermal method to synthesis MgWO4 crystal without crystalline H2O. A pure phase MgWO4 was synthesized by hydrothermal method from Mg(NO3)2 and Na2WO4 solutions. The effects of hydrothermal temperatures on lattice phase, sintering temperatures on the morphology, structure and fluorescence intensity of MgWO4 powder were investigated. Samples were characterized by X-ray diffraction (XRD), fluorescence spectrometer,scanning electron microscope(SEM) and TG-DSC. The results showed that MgWO4 without crystalline H2O molecule can be synthesized at 180~230 ℃ hydrothermal temperatures. The as-prepared sample has a tetragonal structure and transfer to monocline structure when sintered at 850 ℃ or higher temperature. Fluorescence spectra showed that MgWO4 has a broad emission band peaked at 480 nm. The emission intensity becomes stronger as the sintering temperature increases from 750 ℃ to 1 050 ℃. SEM images showed that the size of MgWO4 particles increases with the sintering temperature.关键词：MgWO4;hydrothermal synthesis;crystal transformation116|100|1更新时间：2020-08-12
- 摘要：In order to increase the energy transfer from host to guest in doping organic light-emitting diodes (OLEDs), bis(2-biphenyl-4'-yl-8-quinolinolato)zinc Zn 2 was synthesized and used to assist the energy transfer from N,N'-bis-(3-naphthyl)-N,N'-biphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB) to red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB). OLED with the structure of ITO/NPB/NPB:DCJTB/Zn 2/BCP/Al were fabricated. Without the Zn 2 layer, incomplete energy transfer from NPB to DCJTB led to both emission from host and guest. After Zn 2 was added in to the device, only red emission of DCJTB material was detected in electroluminescence spectra. The efficient emission of DCJTB is achieved via energy transfer with a cascade process from NPB to Zn 2 and then to DCJTB, which results in a complete energy transfer from host to guest. In particular, as the concentration of DCJTB is only 0.5%, red-light-emitting OLED is successfully fabricated using Frster transfer theory at twice. Traditionally, the fabrication of OLED using the assistance material needs thermal evaporation with three sources. However the red OLED only needs two sources, which is very useful in application in the future. In addition, by varying the distance between Zn 2 and the doping system, the efficiency of energy transfer is changed. When the distance is below 10 nm, Zn 2 has an influence on the energy transfer of the doping system. And the longer the distance is, the lower the efficiency is.关键词：organic light-emitting diodes;energy transfer;doping;Zn 2102|139|0更新时间：2020-08-12
- 摘要：The fabrication of flexible organic light-emitting devices (FOLED) is an important development direction in the next generation of display technology. Based on the geometrical optics model, the optical characteristics of our FOLED with a structure of top reflecting mirror/organic material/bottom reflecting mirror/ flexible substrate were discussed. The influence of viewing angle and curvature on the performance of the EL spectrum was studied, the spectrum of FOLED and that of plane OLED were contrasted as well. It was found that:1) When substrate was incurvate, the peak value of the spectrum was blue shift as the viewing angle increasing, and the extent was broader than that of plane OLED. The peak value of the spectrum was blue shift as the curvature increasing; 2) When substrate was excurved, the peak value of the spectrum was red shift as the viewing angle increasing, but the extent was slight; the peak value of the spectrum was red shift as the curvature increasing, the extent was close approximately with that of plane OLED.关键词：flexible organic light-emitting diodes;flexible substrate;viewing angle;curvature;electroluminescence94|103|3更新时间：2020-08-12
- 摘要：A series of high quality MgZnO films are successfully prepared by pulsed laser deposition (PLD) on silicon substrate.It was discovered that with high laser pulse energy deposition the substrate temperature dependence of the structure and luminescence characteristic of the films is not consistent with that under low laser pulse energy. Compared with higher substrate temperature, it is abnormal that the film deposited at room temperature with high laser pulse energy exhibits narrower full width at half maximum (FWHM) of X-ray diffraction (XRD), bigger grain size and roughness of root mean square (RMS) by atomic force microscopy (AFM). Moreover, the photoluminescence (PL) spectra show that the intensity of ultraviolet peak was enhanced remarkably and the ratio of ultraviolet peak to green peak is the largest when the film was deposited at room temperature. It can be concluded that the crystal quality of the film deposited with high laser pulse energy at room temperature is better than that of the film deposited at higher temperature. The growth of MgZnO film consists of plane and column direction, which is the preferred orientation because of lowest surface energy. There is strike of plasma plume against the film during high laser pulse energy deposition, which would result in more particles deviation from film with the increase of substrate temperature. However, even at room temperature the particles directly deposited on substrate have enough residual energy due to high laser pulse energy to form high quality film. The FWHM of XRD of the film deposited with high laser pulse energy decreases as the oxygen pressure increases, which is a indirect proof that the enhanced oxygen pressure would weaken the strike of plasma plume against the film. Our work would be of great benefit to the research of growth high quality MgZnO films on flexible substrate at low temperature.关键词：MgZnO films;PLD;XRD;AFM;PL spectrum107|197|3更新时间：2020-08-12
- 摘要：In an effort to prepare efficient and uniform biolabels, we have developed a novel fluorophore doped polystyrene/silica nanoparticles via sol-gel method. The copolymer precursors are obtained via copolymerizations of styrene and 3-methactyloxylpropyltrimethoxylsilane (KH570). The controlled hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in sol-gel route leads to the formation of near-infrared ytterbium(Ⅲ)- (cyclopentadienyl)tris(diethylphosphito)cobaltate(Ⅰ) anion dyes doped polystyrene/silica nanoparticles. The method significantly reduces fluorescent dye leaching from the nanoparticles, and can be conveniently applied to various dyes molecules with no active group. Scanning electron microscope(SEM) images showed that the nanoparticles are very uniform spherical shape and monodispersed with a diameter of about 100 nm. The present near-infrared fluorescent nanoparticles possess with the values of facilitating bio-modification, biocompatibility, higher detection sensitivity and photo-stabi-lity, and will be well applied in cell recognition, bacterial detection, DNA analysis and so on.关键词：KH570;sol-gel route;composition nanoparticles;near-infrared109|172|0更新时间：2020-08-12
- 摘要：Using the model describing the coupling operation of two paralle waveguides with long-period waveguide grating (LPWG) thereon, the methods decreasing coupling coefficient of coupled modes to realize narrow band-passed optical filtering and high coupling efficiency were investigated in this paper. Meantime, a narrow band-passed optical filter was designed with these methods. The simulation results indicated that the filter could be realized with a single band-passed result and band-rejected result simultaneously in the wavelength range of 1 530 nm to 1 560 nm. The 3 dB band-width is only 1 nm.关键词：integrated optics;electro-optical devices;optical filter;long-period waveguide grating;coupled-mode theory;simulation.102|256|0更新时间：2020-08-12
- 摘要：Tb3+ doped silicate scintillating glass was studied in this paper,we optimized Tb3+ doped silicate scintillating glass matrix,sensitizer,activator contents,improved the melting temperature,holding time,the atmosphere and so on. According to that fluorides have a better rare earth solubility and a relatively lower phonon energy,the fluoride content in the scintillating glass was adjusted. The energy transfer between Tb3+ and Gd3+, Dy3+ was studied according to excitation and emission spectra. The results showed that energy transfer occurs from Gd3+ and Dy3+ ions towards Tb3+ emssion centers as well as the cross relaxation among Tb3+ ions within a certain concentration range exert tremendous effects on the emission intensity of glass. The Tb3+ under the certain concentration range contributes to the enhanced Tb3+ green emission and the weakened Tb3+ blue emission. Therefore,the luminescent property of Tb3+ doped silicate scintillating glass has been noticeably improved.关键词：Tb3+;fluorides;luminescent property137|283|6更新时间：2020-08-12
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The Preparation of ZnO Film by Two Step Chemical Deposition Method and Its Field Emission Properties
摘要：As the cathode electrode of field emitters, ZnO films were deposited under low-temperature and normal atmosphere conditions. To prepare the ZnO clustered rods, a ZnO film was firstly deposited on ITO glass substrates by electrodeposition method as an interlayer.Clustered ZnO rods were then grown on the ZnO films by wet chemical method. The morphology and structure were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray diffraction analysis showed that the ZnO rods are hexagonal wurtzite structure, and the c-axes of rods are mostly along the normal direction of substrate surface. It can be seen that there are a large number of flower-like clusters configuration consisting of many nanorods with diameters in the range of around 300 nm by scanning electron microscopy. This method was proved to be a repea-table, low-cost and high-yield route to synthesize ZnO nanocrystals. The field emission properties of ZnO films were measured with a parallel diode-type configuration in a vacuum chamber.The synthesized ZnO clustered films were used as the cathode, and the ITO glass sheet as the anode. The vacuum in the tested chamber is under 10-4 Pa. The field emission of ZnO films showed that:turn-on field of about 1.3 V/μm and emission current density up to about 909.1 μA/cm2 at a bias field of 5.1 V/μm for the first measurement. Over three times measurements, the field emission is getting stabile. The turn-on field is about 3.0 V/μm and emission current density is 583.3 μA/cm2 at the electric field of 5.8 V/μm. It was proved that it is possible to synthesize clustered nanostructure of ZnO films by two step chemical deposition method, and the prepared ZnO films have good field emission properties. It could be a field emission cathode with charming future.关键词：ZnO film;two-step chemical deposition method;field emission101|265|1更新时间：2020-08-12 - 摘要：Metal surfaces with special morphologies can enhance the fluorescent emission signals of fluorophores at the surface. This phenomenon is named Surface Enhanced Fluorescence (SEF). Up to now, many investigations have been carried on SEF, various kinds of theoretical models have been raised to understand the mechanism of the observed SEF effects. This paper will try to analyze and understand the proposed enhancement mechanisms of the SEF from the point of physics, explore the physical processes and relations of local field enhancement, energy transfer, and plasmon coupled emission models. The influence of the distance between the fluorophore and the metal surface on the enhancement defect will be discussed, too.关键词：surface enhanced fluorescence;local field;energy transfer;plasmon coupled emission195|649|14更新时间：2020-08-12
- 摘要：Watt-level high power InGaN-based blue LEDs were packaged using a traditional packaging method, and their luminous flux, electric power, luminous efficiency, emission spectra and chromaticity coordinates were measured under different forward current (IF) from 50 to 1 000 mA, with a current interval of 50 mA. The results showed that the luminous flux rises sub-linearly, but the luminous efficiency declines with the increase of IF. When the temperature rises with the increase of drive current, the carrier kinetic energy enhances, and then more non-equilibrium electrons diffuse out of the quantum wells, which could result in the decrease of luminous efficiency. The spectrum morphologies and the peak wavelength λp shows a slight blue-shift with the increase of IF from 50 mA to 450 mA, which is related to the influence of In ingredient and the leveled band-gap at a proper high current. The blue-shift values are different between different blue LEDs. However, when IF increases from 500 mA to 800 mA, λp shows a slow red-shift due to the temperature dependence of band-gap energy, and the electron-hole pair recombination luminescence mechanism. In addition, full width at half maximum (FWHM) of the InGaN-based blue LED emission spectra is widened, and the reason was analyzed by the model of configuration coordinate. Moreover, the chromaticity coordinate x, y also changes at the same time.Photometric, chromatric and electric characteristics of blue LEDs make important contributions to chip manufacture and the high power white light LEDs, especially, to the high color rendering warm white LEDs.关键词：high power;InGaN-based blue-LED;blue-shift;red-shift92|272|5更新时间：2020-08-12
- 摘要：ZnO/SiO2 composite film was deposited on glass substrates by means of sol-gel method. The crystal structure and morphology of samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM),respectively. The transmittance and photoluminescent properties of ZnO/SiO2 composite film with different concentration of ZnO were studied. The results indicated that the composite film is composed of SiO2 and ZnO two kinds of oxide after annealed in air at 500 ℃, and the crystal particle size calculated by Scherrer formula is 18.7 nm. The results of SEM showed that two-layer structure can be observed clearly. Selected area diffraction (SAED) indicated that the structure of ZnO/SiO2 composite film is polycrystal. Transmittance of film decreases with the content of ZnO increasing, and the band gap diminishes from 3.5 eV to 3.2 eV, which indicates that optical absorption edge moved to long wavelength. The PL spectra show there are two luminescence locations under 355 nm light excitation, one is the broad emission peaked at 384 nm and the other is the blue band peaked at 440 nm. Both of them are attributed to the electron-hole recombination and defect luminescence of ZnO,respectively. In this paper, the coating method is that two kinds of solution are coated, respectively. So, the two-layer structure of ZnO/SiO2 composite film must be considered. As there is a ZnO/SiO2 interface in the two-layer film, so the structure defect, bond defect and the deep level centers caused by crystal lattice aberrance would be formed after annealed at 500 ℃, these defects and deep level centers can influence the photoluminescent properties of composite film in a certain extent. At the same time, defect center (O—Si—O) of oxygen deficiency in SiO2 could contribute to the blue emission, too.关键词：composite film;sol-gel;transmittance;PL90|139|1更新时间：2020-08-12
- 摘要：The noise properties of quantum cascade laser were investigated by using rate equations, which include the Langevin noise sources and the spontaneous emission factor, to make simulation calculation. The calculated results show that the intensity of noise and the 3dB cut-off frequency width simultaneously decrease, while increasing the spontaneous emission factor. The further research denotes that the spontaneous emission factor takes an obvious effect on the noise properties as the bias current is low, and this effect will be wea-kened by increasing the bias current.关键词：QCL;noise;rate equation107|175|0更新时间：2020-08-12
- 摘要：To the structure of photonic crystal (AB)m(CD)n(BA)m, when choosing proper structural parameters, its transmission spectra is calculated and simulated by means of the transfer matrix method. At the central frequency of the reduced units 0.5(ωa/2πc), when the transmission band of photonic crystal (CD)n is completely inside the band gap of photonic crystal (AB)m(BA)m, both sharing the same central frequency as their symmetry centers, mirror symmetrical photonic quantum well is formed. At both sides of the central frequencies in the reduced units in the transmission spectra of the well, there are odd resonance-peaks, which symmetrically distributed and orderly localized, and form an obvious quantization effect for transmission-peak. The number and the location of the transmission peaks can be modulated by changing the number of period n of photonic crystal (CD)<em>n. This could be used for designing the adjustably odd-passage filters.关键词：photonic crystal;quantum well;resonance transmission;filter106|134|4更新时间：2020-08-12
- 摘要：The theoretical analysis and numerical calculations of TiO2 particle's light scattering characteristics were carried out using Mie scattering theory. Moreover, the distributions of scattering intensity and scattering angle, polarization rate and scattering angle, scattering intensity and size parameter X, optic section and particles radius were presented. The result showed that the larger radius of particle is, the larger forward scattering intensity is;the absoption cross-section and scattering cross-section possess of a peak value when particle's radius is approximately 50 nm for TiO2 nanoparticle.关键词：Mie scattering;optic section;scattering intensity;TiO2122|247|0更新时间：2020-08-12
- 摘要：A high quality factor and low loss optical microcavity structure is employed to construct electrically pulse pumped organic laser device. A 4-(dicyanomethylene)-2-i-propyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTI) doped tris(8-hydroxyquinoline)aluminium (Alq3) film serves as gain layer. IVO and Al films serve as anode and cathode, respectively. The surface-emitting lasing can be observed from the cathode side with the emission peak of 622 nm and threshold current density of 860 mA/cm2. The main key techniques are discussed to realize the laser.关键词：electrically pumping;organic semiconductor;laser129|319|2更新时间：2020-08-12
- 摘要：In this paper, SiO/SiO2 superlattices samples were prepared on Si substrates by electron beam evaporation, and the thicknesses of SiO layers are 2 nm and 4 nm, 4 nm for all the SiO2 layers. The samples were annealed in nitrogen atmosphere at high temperature subsequently. And then,Ce3+ with a dose of 2.0×1014 cm-2 and 2.0×1015 cm-2 respectively was implanted into these samples with formed Si nanocrystals. After Ce3+ doped, the samples were re-annealing at 600 ℃. The photoluminescence (PL) spectra were observed by the fluorescence spectrometry. The PL spectra showed that the PL intensities of samples were not only dependent on the re-annealing temperature and the dose of Ce3+, but also dependent on the size of nc-Si. The experiment results proved that when the size of nc-Si is 4 nm; the effect of energy transfer between Ce3+ and nc-Si is more distinct.关键词：superlattice;silicon nanocrystal;Ce3+ implantation;photoluminescence125|92|0更新时间：2020-08-12
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