最新刊期
卷 23 ， 期 5 ， 2002
- 摘要：The silicon based optical emitting materials are always the first candidate materials for the optoelectronic IC (OEIC) and its engineering applications, due to its low cost and the excellent compatibility with the advanced Si technology in microelectronics. However, the crystalline bulk silicon is an indirect electronic bandgap semiconductor with very poor light emission efficiency. It has been considered unsuitable for optoelectronic applications. A great challenge to experimenters and theorists is that how to make or design an efficient Si-based light emission material using an advanced technology and physics principles. In recent, several schemes, except porous silicon, have been suggested which include the silicon nanocrystals, c Si/O superlattices (SLs) and dislocation engineering. The light emission efficiency has been improved greatly in these Si-based systems. Based on the review of these new achievements, design a Si-based material with direct bandgap is considered a more direct solution. Because of the interface states in Si-based devices have a slow response rate in optical processes. Avoiding interface states are very important for the high speed optical devices and its applications. However, one does not know any critical rule for designing the newly Si-based materials with a direct band-gap until now. In this paper we suggest an empirical symmetry rule and design a series of Si-based superlattices. The computer simulations indicate that one of these superlattices, Se/Si10/Se/Si10/Se, is a semiconductor with a direct-gap character and its band-gap lie in the infrared range, perhaps, to be lie in the window of minimal absorption in current optical fibers. It is expected that the materials and its devices have the excellent abilities for light emission and other optical properties. In addition, this material is easily compatible with Si microelectronics technologies. Therefore, the material produced from computational design may be having potential applications in the field of the optoelectronics.关键词：Si-based light-emitting material;superlattice;direct bandgap light emission87|117|2更新时间：2020-08-11
- 摘要：Organic light-emitting devices (LEDs) have attracted much attention due to their potential application for flat-panel displays. People apply themselves to develop the light-emitting materials with high performance and light-emitting devices with high efficiency and stability. In this paper, we discuss the design of the molecular structure and the method to improve the emitting characteristics of the LEDs. The materials used for the LEDs include light-emitting materials, carrier-transporting materials, and electrode materials. The performance of these materials can be optimized by the design of the molecular structure. The materials with good performance must have high photoluminescent quantum efficiency, good carrier transporting ability and thermal stability. To date, efficiencies for organic LEDs have been limited by the use of fluorescent emissive materials. This limit arises since fluorescence only involves singlet relaxation, thus eliminating the participation of the triplet exciton population. By employing a phospherescent dye where both singlet and triplet excited states participate, the LEDs internal efficiency can, in principle, be increased by as high as 100%. Another method to improve the emitting efficiency is that employing the Frster excitation energy transfer process. Blending a donor with an emitting acceptor for the energy transfer highly reduces the concentration quenching of the generated excitons. Therefore, the energy transfer in the blend systems works effectively to improve the external quantum efficiency of the light-emitting diodes. But it is difficult for the doping system to produce red LEDs with high luminance efficiency. Because the energy transfer from host to guest is not very complete due to the weak overlap between the emission of host and the absorption of red dyes, and in addition, the concentration quenching at high doping concentration. Recently, there are some reports to use two-step energy transfer to increase the emission characteristics of organic LEDs. The emitting layer of the LEDs are co-doped with three different fluorescent materials (A, B and C), and the energy transfer process is from A to B and then from B to C, which is a promising method for obtaining red LEDs. The structure of the LEDs is important for the improvement of the brightness and emitting efficiency of the LEDs. When design the structure of the LEDs, the match of the energy band and layer thickness and refractive index, and the balance of the injected carriers between the carrier-transporting and emitting layers must be taken into account.关键词：organic light-emitting;triplet excited states;efficiency101|111|2更新时间：2020-08-11
- 摘要：Polymer film light-emitting diodes based on dialkylfluorene-thiophene copolymers with different thiophene content were made. The device structure was ITO/PEDOT:PSS/dialkylfluorene-thiophene copolymer layer/Ba/Al. Typical turn on voltage was about 5V and the highest external quantum efficiency reached 1.8% and the highest current efficiency reached 12cd/A. It was found that the electroluminescent spectra of the LED based on this series of copolyfluorenes could be adjusted effectively by changing the content of the thiophene comonomer. By comparing the spectral variation of the devices along with the increase of the current density or after thermal annealing at different temperatures, it was found that the emission spectra were rather stable when the thiophene content reached 5～10%. For device based on the polydialkylfluorene-co-thiophene with 10% thiophene comonomer, no apparent spectral change was found even if the current density was as high as 520mA/cm2 or after the devices were annealed at 160℃ for 2 hours on hotplate. Mechanism of the spectral adjustment with thiophene content was preliminarily discussed and it was believed that the energy level structures corresponding to the two kinds of conjugated chain segments were hybridized to a high extent. As to the excellent spectral stability of devices with current increasing or thermal annealing temperature, the origin was believed to be the introduction of low bandgap comonomer which had destructed the coplanar structure of polyfluorene main chain and thus increased the energy barrier to form excimer.关键词：polymer light-emitting diode (PLED);electroluminescence(EL);fluorene copolymer;spectral stability87|80|0更新时间：2020-08-11
- 摘要：The polymer light-emitting electrochemical cell (LEC) provides a novel approach for light emission from the conjugated luminescent polymers. However, a phase separation occurs intrinsically in the electroluminescent (EL) device due to the addition of polymer electrolyte. To reduce or eliminate the phase separation, a novel block copolymer was presented as the luminescent polymer for the fabrication of the LEC in this work. The block copolymer is composed of the rigid segments, 1,5-di(3,5-dimethoxystyrylene)naphthalene (DMSN) and the flexible segments, tri(ethylene oxide) (TEO). Optical and electrochemical properties of DMSN-TEO were studied firstly by the absorption, photoluminescence spectra and cyclic voltammetry measurements, and the data show that this copolymer is a typical p-type material with a blue emission in solution. The polymer LEC was fabricated successfully by sandwiching a blend film composed of DMSN-TEO, PEO and lithium triflate between an ITO and an Al electrode, and characterized by current-voltage-luminance characteristics, d.c. response and a.c. impedance measurements. Efficient blue-green light emission of the LEC was demonstrated with an onset voltage at 25V and the maximum EL efficiency of ～42cd/A at 28V. The response time of the LEC is less than 5s. All the results suggest that an improved morphology of the blend film is achieved in the LEC due to the presence of TEO segments in the copolymer. The a.c. impedance data indicate the electrochemical doping mechanism of the LEC.关键词：block copolymer;electroluminescence;polymer light-emitting electrochemical cell;blue-green light-emission106|113|1更新时间：2020-08-11
- 摘要：Ultraviolet resonance Raman spectroscopy (UVRR) is a very powerful tool to study molecular structure and dynamics. Resonance Raman scattering requires excitation within an eletronic absorption band and results in a large increase of scattering, it has the additional benefit of avoiding interference from fluorescence. Furthermore, this method make it possible that selectively excite electrons of different functional groups with different excitation wavelengths in order to study the specific parts molecules. Based on the research work the writer did in Pittsburgh University, This paper introduced the status and recent progresses of UVRR spectroscopy used in the study of protein secondary structure and fuctions, the UVRR studies of photochemical isomerization process for aqueous dipeptides NMA and Gly-Gly. The UVRR experimental main points also be demonstrated. A protein consists of one or more amino acides linked by peptide bonds, they are folded into a specific three-dimentional shape maintained by further chemical bonding, such as hydrogen bonds and disulfide bridges. Since the Raman frequencies and intensities of these amide bonds are sensitive to the secondary structure, it is very important to study UV resonance Raman spectroscopy of proteins. Protein spectra obtained using the excitation at 206.5nm are dominated by amide bands.Thirteen proteins give the average pure α-helix, β-sheet and random coil spectra,these average spectra are used as standards to directly determine protein secondary structure. Protein's biological function is determined by its three-dimentional structure. Since the majority of native protein structure self-assemble,these three-dimentional structure must be encode by the protein's primary sequences.Prediction of native protein structure has become more urgent due to the imminent completion of the sequencing of the human genome. The encoding rules must be complex since for most proteins the primary sequence will encode both the native static structure as well as the folding dynamics. These folding dynamics are likely to be complex. A new method has been developed to measure protein folding and unfolding dynamics. Many native proteins unfold(denature) when the solution temperature is raised or lowed. Using the pump-probe technique the folding and unfolding process was monitored in the time scale when they occur. UVRR spectra are obtained at intervals ranging from ten nanoseconds to several hundred nanoseconds following the heat-producing pump pulse.关键词：ultraviolet resonant Raman spectrum;protein;protein folding and unfolding87|66|1更新时间：2020-08-11
- 摘要：ZnO is a versatile semiconductor material with hexagonal wurtzite structure and has a band-gap of 3.3eV with a large exciton binding energy of 60meV at room-temperature. ZnO has attracted much more interest in the field of the information and display like GaN due to the application of UV emission. In the past, the structure and optical properties of ZnO film has been investigated extensively, in contrast, it is less known about the structure and optical properties of ZnO nanoparticles embedded in dielectric matrix. By utilizing the wave guide structure of ZnO/SiO2 and the optical properties of quantum dots, ZnO nanoparticles embedded in SiO2 can decrease the intensity of the photon scattering and self-absorption and increase the UV emission of ZnO nanoparticles. High quality ZnO nanoparticles embedded in SiO2 was fabricated by zinc ion implantation (160keV, 3×1017 cm-2) into optical-grade silica substrate, followed by post-thermal annealing. The dependence of the component, orientation, average grain size and the quality of ZnO nanoparticles on the annealing ambient and time was studied by X-ray diffraction spectra. The zinc ion implantation with high dose and zinc atoms diffusion from silica surface can give rise to micro-hole, weak bond and breaken bond in silica near the implantation layer. During the annealing process, the disappearance of micro-hole and the reconstruction of weak and breaken bonds will occur. High quality ZnO nanoparticles embedded in SiO2 was obtained as the annealing time increased to 2 hours at 700℃ in oxygen ambient. We can control the average grain size and density of ZnO nanoparticles by sequential post-thermal annealing zinc-implanted silica in nitrogen and oxygen ambient at 700℃. The average grain size of ZnO nanoparticles embedded in SiO2 was in the range 18～26nm. The free exciton absorption and the UV emission of ZnO nanoparticles embedded in SiO2 grown by post-thermal annealing zinc-implanted silica were observed by utilizing absorption spectra and micro photoluminescence spectra at room-temperature. The experimental results indicated that the stress affected the free exciton absorption peak of ZnO nanoparticles. The oxygen atoms that diffused to silica inside can decrease the defects that located in the boundary of nanocrystalline ZnO and were induced by the ion implantation during the annealing process in oxygen ambient. The dependence of the intense UV emission of ZnO nanoparticles on the temperature indicated that the impurity containment in the sample is less. The intense UV emission of ZnO nanoparticles can be attributed to the free exciton emission of ZnO nanoparticles at room-temperature. The relatively intense free exciton emission, the weak binding exciton and the free exciton replica emission of ZnO nanoparticles can be observed at 77K.关键词：ion implantation;ZnO nanoparticles;thermal annealing;photoluminescence;exciton112|46|1更新时间：2020-08-11
- 摘要：ZnS:Mn2+ nanoparticle synthesized by chemical colloid method has been dispersed into PVB ethanol colloid to form organic film. From the emission spectra before and after UV 290nm irradiation, the luminescence peaked at 580nm of Mn2+ 4T1→6A1 transition has a higher enhancement than that ever reported under UV 300nm excitation. The emission spectra, excitation spectra and time-dependent luminescence growth were employed to determine the dynamics of the irradiation-induced luminescence enhancement effect (RILE). The excitation spectra after irradiation showed that there are two excitation peaks,which are corresponding to the 1S and 1P energy state of ZnS, respectively. The 1S excitation peak's shift to the high energy compared with the bulk materials induced by the quantum confine effect, indicates that the average size of nanoparticles is around 3nm by the theory of Effect Mass Approximation (EMA). With the UV irradiation, the shape of excitation spectra changed.The original 1P excitation peak grows more rapidly than the 1S excitation peak and get a higher value when the increment came to saturation. Dynamics of luminescence is investigated. We consider that surface state can quench the luminescence of Mn2+. With the irradiation, the surface state decreases and therefore luminescence of Mn2+ increases. By fitting the experimental data, we find that the relaxation rate from 1P to quenching center has a linear relation with that from 1S to quenching center. We conclude that both 1P and 1S state can relax to quenching center. The enhancement is stable because the reduction of quenching centers is irreversibility. The sample has the same RILE effect after exposure to the natural light, so it can used as a new type of material to measure the dosage of UV irradiation.关键词：nanoparticle;ZnS:Mn;ultraviolet;enhancement99|83|0更新时间：2020-08-11
- 摘要：It has been pointed out that the exponential decrease with pressure of the photoluminescence intensity around 3GPa observed in ZnSe/ZnCdSe superlattices and quantum wells can not be explained by the direct-gap indirect-gap transformation because the direct-gap indirect-gap transformation pressures are estimated as 13.7GPa for ZnSe and 7GPa for ZnSe/Zn1-xCdxSe(x=0.26) superlattices and quantum wells. But till now, no detailed calculations for the transformation pressures have been reported for the ZnSe-based heterostructures. In order to understand better the properties of ZnSe and ZnSe-based heterostructures under pressure, we studied the hydrostatic pressure dependence of the Γ,X and L energy band minima for bulk ZnSe and the ZnSe epilayer of ZnSe/GaAs heterostructures using the empirical pseudopotential method. The pseudopotential form factors at various pressures are obtained by scaling the atmospheric pseudopotential form factors in terms of the electron effective mass or the energy-gap and the results show that the method of the energy-gap scaling, which is proposed in this paper for the first time, is better than the electron-effective-mass scaling. The transformation pressures of bulk ZnSe and the ZnSe/GaAs epilayer are calculated as 13.5GPa and 9.5GPa with the energy-gap scaling. By fitting the curves of the energy band minima versus pressure, we also obtained the pressure coefficients of the Γ,X and L energy band minima of bulk ZnSe. The corresponding pressure coefficients are 0.211 3eV/GPa, 0.071 4eV/GPa and 0.153 5eV/GPa respectively. It can be seen that the pressure coefficient of the X minima of ZnSe is positive, which is different from that of Si, Ge and GaAs semiconductor materials. On the other hand, the pressure coefficient of the X minima of ZnSe is smaller than that of the Γ minima, so the transformation from direct-gap semiconductor to indirect-gap semiconductor of bulk ZnSe can still occur but needs much greater pressure. It is also shown that the pressure coefficients of the ZnSe epilayer in a ZnSe/GaAs heterostructure are obviously affected by the build-in strain caused by lattice-mismatch between the epilayer and the substrate. This is the reason why the transformation pressure is larger for ZnSe-based heterostructure materials.关键词：hydrostatic pressure;heterojunction;direct-gap indirect-gap transformation;pressure coefficient110|150|0更新时间：2020-08-11
- 摘要：Metal-semiconductor-metal ultraviolet photodetectors have been fabricated on undoped GaN films grown by metalorganic chemical-vapor deposition. Response dependence on wavelength, voltage bias and chopper frequency has been extensively investigated both at room tempe rature and at 94K low temperature. The results show that the response time drops by more than three levels of magnitude when the incident light's wavelength increases from 360.to 450nm at 94K. For the incident light less than 360nm, its response time at 94K is about one level greater than that at room-temperature. An increase in response time was also observed at 94K.关键词：metal-semiconductor-metal (MSM);GaN;photodetector;94K;room-temperature108|75|1更新时间：2020-08-11
- 摘要：Indium gallium arsenic are now of considerable commercial importance in optoelectronics. For example HBT, HEMTs, FET and Detectors. Very high quality is required to fabricate these devices, in terms of electrical and optical properties. The epilayer properties are known to be very sensitive to growth parameters (growth temperature,Ⅴ/Ⅲ ratio, etc.). It is important to find suitable growth temperature for good quality epilayer properties. The effects of growth temperature on solid composition, surface morphology, crystal quality and electrical properties were investigated for InGaAs. In0.53Ga0.47 As was grown by low-pressure metalorganic chemical-vapor deposition on semi-insulating Fe-doped InP substrate. The substrates were misoriented 2～5° toward (110). Precursors were trimethylindium(TMIn) and trimethylgallium(TMGa) for group Ⅲ, arsine(AsH3) and phosphine(PH3) for group Ⅴ. The growth temperatures ranged from 500～680℃. Before the epitaxy of InGaAs, an InP buffer layer was grown with 0.1μm. The composition of InGaAs was determined by X-ray diffraction. The surface morphology was examined with SEM. Electrical properties were investigated by Hall effect measurements at room-temperature. The mirror like and featureless morphology of In0.53Ga0.47 As epilayer was attained. In order to keep indium solid composition constant, TMIn vapor composition increase with growth temperature increasing. The pyrolysis temperature of TMGa is higher than that of TMIn which pyrolyzed completely at 500℃. In the range of 500～650℃, the TMGa pyrolysis efficiency increase rapidly with increasing growth temperature. In the range of 650～680℃, because of a larger volatilization rate of indium from surface which is greater than that of gallium, the surface morphology became rough above 680℃. The FWHM of X-ray rocking curve is a good indication of the epilayer quality. A plot the X-ray rocking curve FWHM as a function of growth temperature show a low values between 630℃ and 650℃ but it rises at both higher and lower temperatures. The mobility increase with growth temperature increasing under 630℃. The mobility decrease with growth temperature increasing above 630℃.The best mobility can be obtained at 630℃. At low growth temperature the carrier concentration increase dramatically. This is attributed to enhance carbon incorporation.关键词：InGaAs;growth temperature;LPMOCVD99|76|3更新时间：2020-08-11
- 摘要：The In0.5(Ga1-xAlx)0.5 P quaternary alloys has been an interesting material,because of high recombination probability,high emission efficiency, direct band-gap transition and small lattice-mismatch to GaAs substrate.Thus In0.5(Ga1-xAlx)0.5 P alloys was ideal active and cladding layer material for LEDs and LDs operating in the red to green region of the visible spectrum. However,many problems plague the MOCVD growth of In0.5(Ga1-xAlx)0.5 P,including oxygen and carbon contamination,due to the Al,the difficulties increases as the band-gap energy increases. The In0.5(Ga1-xAlx)0.5 P materials were grown on the silicon doped GaAs substrate by LP-MOCVD.The metalorganic precursors were trimethylindium(TMIn),trimethylgallium(TMGa),trimethyaluminum(TMAl).The hydride source was phosphine(PH3).The dopant source was silane(SiH4) and dimethylzinc(DEZn),respectively.Al composition in In0.5(Ga1-xAlx)0.5 P epilayer was x=0.6. To investigate the effect of the growth conditions such as temperature,dopant flow rate,Ⅴ/Ⅲ ratio,Al composion and substrate orientations on doped concentration,the growth of doped InGaAlP alloys was studied by LP-MOCVD.We demonstrated that lowering temperature and reducing Al composion,increasing the flow rate of DEZn,and selecting the substrate inclining 6 to 15° from <100> to <111> are contribute to the increasing of Zn-doped concentration in InGaAlP alloys. While raising temperature and increasing the flow rate of SiH4,reducing Al composion and Ⅴ/Ⅲ ratio are contribute to Si doped concentration,and the orientations of substrate has no effect on the latter.关键词：InGaAlP;LP-MOCVD;dopant;doped properties95|72|0更新时间：2020-08-11
- 摘要：Light emitting diodes are shown to be excellent sources for illumination if the problem for promoting light-emitting efficiency is solved. The optical efficiency of a conventional light-emitting diode is usually less than 5% because most of the light emitted in the active region inside the diode cannot escape out of the diode. How to promote the optical efficiency of light-emitting diodes attracted great attentions in recent years. We present a diode structure with two photonic crystal layers added to a conventional light-emitting diode. One photonic crystal layer, with a parabolic surface shape, reflects the light from the pn junction travelling sideways to the direction near the axis of the parabolic surface, so that they travel in a small solid angle along the axis and can escape out of the diode. Another photonic crystal layer, shaped like a disk, reflects light travelling in the opposite direction to the output direction, so that the diode emits light just in one direction. In the structure, the pn junction is at the focus plane of the parabolic photonic crystal layer. We find that for the diameter of the pn junction region being 2 F and the distance from the focus plane to the output surface being H=63.83 F, all the light from the pn junction can go out of the diode, thus a nearly 100% optical efficiency can be achieved. Here F represents the focus length of the parabolic surface. As an example, we designed a high efficiency light-emitting diode operating in the wavelength region from 1 250～1 850nm with the central wavelength being 1 550nm. The photonic crystals designed in the example are made of PbTe and Na3AlF6. The thickness of each kind of material in each period is 127.42nm. The photonic crystals are designed to be of 15 periods and of one-dimensional in structure. The structure presented in this paper can be applied to diodes operating at any other wavelength region. The light-emitting diode presented in this paper is unique in structure, efficient for operation, and more easy and practical for production than those adopting two dimensional photonic crystals investigated before.关键词：light-emitting diode;photonic crystals;photonic band-gaps;parabolic reflector102|126|3更新时间：2020-08-11
- 摘要：This paper manifested a catastrophic damage due to electrical damage during the measurement. However, electrical surge is caused by external conditions such as an electrical biasing situation, as a result, the p-n junction is damaged or breakdown so that the current-voltage relation become electrically short at the instantaneous current, which can be manifested from the P-I curve and V-I characteristics: a sudden decrease in light output power is observed, moreover, the voltage is no longer changing dependence on the increasing of current with the drop-off of output power. According to N. I. Katasavets, et al., a conclusion can be made that fact overheating at J<2 000/cm2 in all types of LDs is due to the absorption of intrinsic laser radiation at the facet and to process nonradiative surface recombination. Facet overheating has superlinear dependence on output optical power. Then through the scanning electron microscopy (SEM), we indeed find that the melting region occured, also there is cracks at the facet which may be brought by the stress-induced by cleaving to form the facets, so laser no longer stimulated emitting, by contrast, another rapid degration is also shown in the paper, at the same time, both degrations were analyzed on the basis of theory, which manifested the degration of laser are principally due to material, structure and process of the laser, electrical surge is only accelerate the degration which origined from material or fabrication, but it is still important to understand the catastrophic or rapid damage related to electrical surge during the device measuring.关键词：electrical surge;catastrophic damage(CD);laser diodes(LD)96|124|1更新时间：2020-08-11
- 摘要：The properties of the polaron in crystals influence the properties of crystals very remarkably. The properties of the polaron for polar crystals have been of considerable interest.The polaron problem has been studied by many theoretical and experimental method by many investigators.Huybrechts calculated the ground state energy of the polaron. By means of vibrational scheme,the ground state energy,the effective mass and the mean number of phonons of polaron are derived by Tokuda. We discussed magnetic field and temperature-dependence of a magnetopolaon by using a Tokuda's method. The polaron features of the one-dimensional Holstein model are investigated by Cataudella,Filippis and Iadonisi by improving a variational method introduced recently and based on a linear superposition of Bloch states that describe large and small polaron wave functions.The mean number of phonons are calculated and discussed.However,the research on the magnetic field and temperature-dependence of the mean number of phonons in a magnetopolaron has not been studied so far.In this paper,the magnetic field and temperature-dependence of the mean number of optical phonons for a magnetopolaron in polar crystals are investigated by using a linear combination operator method.The results show that for the weak coupling the mean number of optical phonons N will increase with increasing temperature T vibrational frequency λ and magnetic field B and will increase with decreasing coordinate z,whereas for the strong coupling will N increase with increasing λ,z,B and T.关键词：magnetopolaron;mean number of optical phonons98|162|0更新时间：2020-08-11
- 摘要：The absorption spectra of Er3+ ion and Yb3+ ion in tellurite glass were investigated. The peak absorption were marked according to the absorption transition of Er3+ and Yb3+, the energy levels of Er3+ and Yb3+ ions in tellurite glass were obtained according to the absorption spectra. The emission spectrum of Er3+ ion in tellurite glass was studied. The stimulated emission cross section was calculated using McCumber theory and the FWHM was obtained according to the emission spectrum. Er3+ ion show higher emission cross section(σp=7.5×10-21 cm2) and larger FWHM (FWHM=66nm) in tellurite glass than those in other glass hosts, which are very important parameters for optical amplifiers to realize broadband and high gain amplification. The upconversion spectra of Er3+ ion in tellurite glasses were measured and analyzed. The much lower phonon energy of tellurite glass makes it has different upconversion mechanism compared with other glasses with relative higher phonon energy. The relative longer lifetime of 4I11/2 level of Er3+ ion in tellurite glass produces the upconversion process 4I11/2+4I11/2→4F7/2+4I15/2 much more serious, and the four emission transitions 4F7/2→4I15/2, 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 which corresponds to 486,530,550.and 660nm emission, respectively, become obvious. Furthermore, the upconversion intensity enhances with the increase of Yb3+ concentration. Upconversion emission is very harmful for fiber amplifiers, which not only reduces the efficiency of bump light, but also deteriorates the noise figure of the amplifiers, so it is important to reduce upconversion phenomenon as much as possible. The energy transfer mechanism between Er3+ and Yb3+ ion were analyzed. The energy transfer coefficients and efficiencies between Yb3+ and Er3+ were calculated. At a certain Yb3+ concentration, the forward energy transfer coefficient and efficiency hardly change while the back energy transfer coefficient and efficiency increase monotonically. So the effective sensitization of Yb3+ to Er3+ is appropriate only at a certain range of Yb3+ concentration. The right selection of Yb3+ concentration is needed in order to realize effective bump.关键词：spectroscopic properties;tellurite glass;energy transfer;Er3+ ion98|116|2更新时间：2020-08-11
- 摘要：The temperature-dependence of emission intensity of the Eu3+-ion in several silicate glasses was investigated from 77K to 670K, by the excitation of a non-resonant 488nm laser. It was observed that the total emission intensity of the Eu3+-ion in some glasses had a maximum at a certain temperature below 670K, while in the other glasses the intensity increased monotonically with temperature. A unified theore tical model was given considering thermal activation, phonon assisted absorption and nonradiative energy transfer processes. Based on the model, all of the experimental data were well fitted. The temperature quenching channels were discussed, while the temperature quenching rates were determined. As known, persistent spectral hole burning (PSHB) has potential application as the media of high density optical information storage. Recently, PSHB phenomenon at room-temperature has been observed in Eu3+-doped as well as Sm2+-doped glasses. For this sake, Eu3+-ion doped in glass hosts is attracting current interests. In this paper, we study on the temperature-dependent characteristic of the emission of the Eu3+-ion under the pump of a 488nm light. The understanding of temperature-dependent luminescent process is helpful to search for new materials for optical storage at high temperature and phosphors with high quantum efficiency. In our study, the variation of the emission intensity of Eu3+ can be mainly attributed to two factors, the thermally excited emission from 7F2 to 5D2 and the temperature quenching effect. The former tends to cause the emission intensity of Eu3+ increase with temperature, while the later tends to cause the intensity decrease. The temperature-quenching effect is comparable with the thermal excited emission of 7F2→5D2 when the glass is elevated to one certain temperature, thus a maximum of emission intensity occurs. In all the glasses, the phonon assisted transition rates from 7F0to 5D1 and 5D2 and from 7F1 to 5D1 and 5D2 are much smaller than the resonant transition rate of 7F2→5D2.关键词：silicate glass;thermal activation;phonon-assistant absorption;non-radiating energy transfer;temperature quenching134|114|1更新时间：2020-08-11
- 摘要：Since its invention in the nineteenth century, the long afterglow phosphors have been improved greatly. Up to 1990s, the best product is metal sulfide long afterglow phosphors. The aluminates long afterglow luminescent material was invented at the beginning of the nineties, its luminescent brightness, long afterglow characteristics and stability were obviously superior to the above sulfide series products. However these phosphors still have bad anti-moisture character, and they have strict restriction over the raw material's purity and form, besides, the production cost was higher, therefore it also can not satisfy the requirement of usage very well. In 1998, silicate long afterglow phosphors are synthesized successfully, which having excellent chemistry stability. What is more, the development of red long afterglow phosphors also made great progress. The brightness of the best red phosphors is six times than that of CaS, the decay time is about 6～8 hours. Base on lots of literatures and experiments, the development, type, preparation and mechanism of the long afterglow phosphors are studied, and the properties of phosphors are compared with them in this paper.关键词：luminescence;long afterglow material;preparation method230|236|24更新时间：2020-08-11
- 摘要：In the design of powder phosphors, the morphology and size of materials must be studied and controlled so that the desired objectives of improved powder phosphors can be achieved.It has been pre dicted that the optimum phosphor characteristics can be obtained with particle size on the order of 1μm. For the improved phosphors, the ideal morphology is that of perfect sphere. Spherical morphology is required for high brightness and high resolution. Additionally, high packing densities and low scattering of light can also be obtained by using spherical phosphors. A range of methods has been developed for the preparation of spherical particles. Spray pyrolysis is a newly developed method for the preparation of inorganic functional materials. In general, luminescent materials derived from this method have spherical morphology and fine narrow size distribution. In this method, a misted stream of precursor solution is dried, precipitated, and decomposed in a tubular furnace reactor. Particles produced by spray pyrolysis are relatively uniform in size and composition because of microscale reaction within a droplet and the lack of a milling process. Moreover, various preparation conditions have influence on the characteristics of particles prepared by spray pyrolysis.Therefore, the morphology, composition and size of particles can be controlled for good luminescent characteristics by changing the concentration of solution, spray rate, flowing rate of carrier gas and characteristics of solution. Accordingly, the luminescent intensity of powder phosphors prepared by spray pyrolysis can be improved with the changing of characteristics of particles caused by sintering temperature, morphology and size, crystallization and additive. Despite good luminescent performance, spray pyrolysis method also has a number of advantages such as simplicity of apparatus, low costing and without pollution. In conclusion, spray pyrolysis method can be a hopeful developing direction for preparation of powder phosphors.关键词：spray-pyrolysis;sphere;luminescent material152|138|8更新时间：2020-08-11
- 摘要：A perfect nonabsorbing microsphere with higher refractive index than that of surrounding medium is a good microcavity.Inside such a sphere, which has a diameter of a few microns,there exist a discrete number of resonant optical modes,so-called whispering-gallery modes(WGMs).The spontaneous emission cross sections at the microcavity resonance photon energies are larger than the bulk spontaneous emission cross sections because of the modified photon density of states of the microcavity.Such microcavity structures can be used for efficient optical devices such as low-threshold laser and low-power nonlinear optical devices. In this work, The TiBa glass microspheres doped with Er3+ for morphology dependent resonances of up conversion emission were designed. The glass sample components are 25TiO2-27BaCO3-8Ba(NO3)2-6ZnO-9CaCO3-5H3BO3-10SiO2-7water glass-3 Er2O3(wt.%).The raw materials were completely mixed in deionized water to form slurry.Then the slurry was dried and ground to small pieces,and blown off by a gas burner.The small pieces were melted and formed into microsphere,and cooled in air.We measured the Raman spectra of the microspheres and made sure that the material in the microspheres is in vitreous body. The experimental apparatus is micro-Raman spectrometer(RENISHAW System 2000).The laser beam,wavelength 633nm,was focused into a ～5μm spot by an objective lens(20x,numerical aperture 0.4) and irradiated on a singe glass microsphere under an optical microscope.Emission from the microsphere were collected by the same objective lens,and the spectra were observed by the spectrometer(with CCD). The emission spectra of TiBa glass and a TiBa glass microsphere(about 46μm in diameter) were measured under 633nm excitation and discussed.We have proved the green upconversion luminescences to be from 2H11/2→4I15/2 (for 525nm) and 4S3/2→4I15/2 (for 548nm)due to two-photon absorption.The strong morphology-dependent resonances of up-conversion luminescences in the microsphere(about 46μm in diameter) were observed.The observed resonances could be assigned by using the well-known Lorenz-Mie Formalism.关键词：upconversion emission;Er3+-doped glass;glass microsphere;morphology-dependent-resonances123|77|0更新时间：2020-08-11
- 摘要：Microchannel plate (MCP) is a device of two-dimension array electronic multiplier. The detection ability to 40～60keV X-ray for MCP was increased by coating the halide such as CsI, CsBr and KBr on input plate of MCP, that forming a reflection X-ray sensitive film in the channel with depth of 2～3 times of diameter below the input plate. Experiment results shown that the output response of MCP with variable density structure of CsI for X-ray is about 5～6 times higher than that with constant density structure, and of one order of magnitude stronger than that without coating the film. Comparatively, the output response of MCP with CsI sensing film is best,but CsBr and KBr medium are not. The response characteristics of MCP with CsI for X-ray related to film materials, structure, component distribution and fabrication process. Several experiment curves denoted the response characteristics to X-ray at different target voltage and current. The results basically accorded with the theory about quantum detection efficiency of reflection X-ray cathode. This new MCP reflection X-ray sensitive film of variable density halide has been successfully applied on X-ray imaging detecting devices. The corresponding detection system will find widely and potential applications in the field of medical diagnosis, nondestructive evaluation and security inspection etc.关键词：variable density;halide;X-ray photocathode;microchannel plate142|114|1更新时间：2020-08-11
- 摘要：Two-TFT pixel driving circuit was simulated and analyzed for Active Matrix OLED using AIM Spice in this paper.From the simulation results,the influences of the driving transistor T2 W/L ratios on the OLED current were shown.For a typical OLED emission efficiency,and a known pixel area,a current level is needed to achieve the pixel brightness.By the simulation results,reasonable T2 W/L ratios can be obtained.The simulation results also showed that the OLED grayscale could be adjusted by changing the data voltage.On the other hand,the source voltage should be high enough to ensure the T2 operates the saturation state.Further more,the two-TFT pixel electrode circuit transient characteristic was simulated.The impact of the T1 W/L ratios and storage capacitor on output characteristic was discussed.The lower size capacitor will reduce the OLED current during the pixel electrode OFF period.And too large capacitor will deduce a large charge time constant,which impacts on the respond speed and brightness of OLED.The larger T1 W/L ratios will also result in the drop of the OLED current during the pixel electrode OFF period.So they need to be carefully selected.From the transient characteristic of the influences of the value of scan pulse voltage on output current,it is clear that the lower scan voltage value will result in the OLED current is not proportional to data voltage.Thus the OLED brightness cannot follow the variation of the data voltage.The increasing of scan voltage value will solve the above problem. Form the temperature characteristic,the two-TFT pixel driving circuit cannot overcome the effect on OLED current because of the shift of threshold of the driving TFT due to the manufacturing variations and the circuit aging. The simulation results indicate that if the parameters are chosen properly,driving circuit can ensure the OLED brightness requirement and the constant output current in a frame time,and the grayscale can be adjusted by changing data voltage.Simulation results showed the various parameter effect on the circuit performance.On this basis,we obtain the more reasonable parameter value about two-TFT pixel electrode circuit.Those analyses supply base for driving circuit design,parameter choice,performance analyses and layout design for Active Matrix OLED.关键词：TFT pixel driving circuit;active matrix OLED;AIM-Spice;simulation analysis107|155|1更新时间：2020-08-11
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