最新刊期
卷 25 ， 期 6 ， 2004
- 摘要：The problems of an electron bound in a hydrogenic impurity and interacting with the longitudinal optical phonon field of an ionic crystal or a polar semiconductor have been of considerable interest. Since To-kuda investigated the problem of bound polaron by using variational scheme of the Lee-Low-Pines theory, many investigators studied the properties of the bound polaron by means of various theoretical methods and experimental methods. Lepine et al. studied the properities of bound polaron in a narrow-band polar crystal within the scheme of effective-mass approximation. Chen et al. studied properties of bound polaron in parabolic quantum wire by using the Feynmann-Haken path-integral approach.Liang et al. investigated binding energy of bound polaron in ternarg mixed crystals, taking into account the interaction of an electron with two branch longitudinal optical phonon.Es-sbai studied LO phonons effect on the binding energy of impurity bound polaron in 3D GaAs quantum dot by using variational method. Molnikov discussed the effect of the electron-phonon interaction on an electron bound to an impurity in a spherical quantum dot by using adiabatic variational method. Devreese studied properities of bound polaron in oxide compounds by using quantum-chemical method.The properties of a strong or a weak coupling bound magnetopolaron was discussed by using a linear combination operator and a unitary transformation methods by the present authors. In the past, most work was devoted at zero temperature.In fact, the case of a finite temperature is more significant.However, the temperature dependence of the properties of bound polaron has not been studied so far.In this paper, the temperature dependence of effective mass of bound optical polaron which is in a strong or a weak-coupling with optical phonon was calculated by using improved linear combination operator and unitary transformation method. Numerical calculations, for the RbCl crystal, as an example, are pertormed and the results illustrate that the vibrational frequency and the effective mass of the strong-coupling bound polaron increase with increasing the temperature and the Coulomb potential.关键词：bound polaron;improved linear combination operator;effective mass;temperature dependence95|96|0更新时间：2020-08-11
- 摘要：We designed and manufactured an optical bistability waveguide device based on nonlinear one-dimensional photonic crystal used CdSxSe1-x doped glass. This kind of semiconductor doped glass has large nonlinear refractive index and nonlinear fast response time. The distribution of refractive index of the nonlinear one-dimensional photonic crystal waveguide satisfies sine function. We obtained the nonlinear photonic crystal waveguide by exposure holography and etching techniques. Length of the photonic crystal waveguide is about 3 mm. The height of the peak-groove of the waveguide is 0.1 μm. According to our design, the center of bandgap of the one-dimensional photonic crystal lies at 514.5 nm while the power density of the incident light, the incident light was reflected by the photonic crystal. When the power density of the incident light increasing, the bandgap is shifting to the direc-tion of short wavelength due to the decreasing of the refractive index with the increasing of the incident power density, so more incident light is transmitted. In experiment, we used an active mode-locking pulse of Ar ion laser as the light source which wavelength is 514.5 nm, repeating frequency is 82 MH z and pulse width is 200 ps. The light beam was coupled into the device by prism with a laser average power of 1.28 W (in the case of nonlinear saturation operation, optimum coupling efficiency is about 6%). Pulse wave forms of incident light and transmitted from sample were recorded in turn by 7904 oscilloscope. The optical bistability curve of input power density and output one is fitted by computer. We obtained the threshold power density of bistable switch to be 1.60×105 W/cm2 (it is equivalent to average power of 77 mW) and both the rise and fall time are 63 ps. We used the Finite Difference Time Domain Method to obtain the characteristics of the bandgap shift with the incident power density increasing of the nonlinear photonic crystal and calculate the optical bistability curve of this device. In theory, the threshold power density of bistable switch is about 1.40×105 W/cm2 and the switch time is about 50 ps. The theoretical results agree well with the experimental ones. This device is a new and feasible one for optical information process and optical computing in the future.关键词：one-dimensional photonic crystal waveguide;optical bistability;nonlinear100|79|0更新时间：2020-08-11
- 摘要：In recent years, the rapid advances of nanofabrication technology have made it possible to work with quasi-zero-dimensional quantum dot in laboratories. The electron energy spectrum of such quantum dot is fully quantized. Such systems are of great interest in fundamental studies, as well as in practical applications for microelectronic devices. There exist numerous works that have demonstrated the significant influence of electron-phonon interactions on the electronic, optical, and transport properties of microstructures such as quantum wells, quantum wires, and quantum dots. Other people studied the effects of electron-phonon on the quantum dots by the second-order Rayleigh-Schrodinger perturbation theory or the Landau-Pekar variational treatment. In this paper, we investigate weak-coupling polaron’s properties in a parabolic quantum dot by the linear combination operator in the first time. It is shown that the ground state energy and binding energy decrease with increasing the effective confined length of the quantum dot. The result presents the polaron ground state energy of parabolic quantum dot is as a function of the effective confinement length. They show the variation of the electron-phonon coupling strength has very small effect on the polaron binding energy of parabolic quantum dot in the profoundly weak effective confinement length field. But, the variation of electron-phonon coupling strength has obvious effect in the strong effective confinement length field. They will turn to bulk structure crystal when the effective confinement length intend to infinite. Also, indicate the polaron binding energy of parabolic quantum dot is as a function of effective confinement length. It is evident that the variation of the electron-phonon coupling constant has no effect on the polaron binding energy of parabolic quantum dot. In one word, the confine of parabolic quantum dot strengthens the ground state energy.关键词：quantum dot;linear combination operator;weak coupling108|70|0更新时间：2020-08-11
- 摘要：Solitonlike in the one-dimensional photonic crystals with Kerr nonlinearity was investigated. The relationship between solitonlike and the incident intensity, Kerr coefficient or linear photonic quantum well was calculated. It was found that with the reduction of linear photonic quantum well, rich and varied solitonlike electromagnetic modes appear in the gap. The lower linear photonic quantum well, the less the incident intensity of the first solitonlike appear. Although nonlinear is the essential reason caused solitonlike, the height of linear photonic quantum well play an important role.关键词：photonic crystal;Kerr nonlinearity;solitonlike112|116|1更新时间：2020-08-11
- 摘要：With the increasing development of organic opto-electronic devices, interest in the mechanisms of charge carrier photogeneration, separation, transport and recombination continues to grow. Electromodulation of photoluminescence has been used as an efficient probe to investigate evolution of primary excitation in an electric field. This method can provide useful information on carrier photogeneration, the formation and dissociation of excitons, energy transfer, and exciton recombination in the presence of an electric field. Operation of organic light emitting diodes(OLED) brings electrons and holes from opposite electrodes and generates singlet and triplet excitons. However, triplet excitons are wasted because a radiative transition from triplets is spin-forbidden. Spin statistics predicts that singlet-to-triplet ratio is 1:3 in organic semiconductors. One way to harvest light from triplet excitons is to use phosphorescent materials. These materials incorporate a heavy metal atom to mix singlet and triplet states by the strong spin-orbit coupling. As a result, a spin forbidden transition may occur allowing an enhanced triplet emission. Among phosphorescent materials, factris(2-phenylpyridine) iridium [Ir(PPY)3] has attracted attention because of its short triplet lifetime to minimize the triplet-triplet annihilation. High quantum efficiencies were obtained by doping Ir(PPY)3 in organic molecules and in polymers. The mechanisms of electrophosphorescence has been a interesting topic since high efficient electrophosphorescence was reported. In this paper, we investigated the PL spectrum under the operation condition of OLED based on phosphorescent materials doped polymer. The photoluminescence under the modulation of an electric field and electroluminescence from thin films of poly(N-vinylcarbazol) (PVK) doped by Ir(PPY)3 are measured. The PL spectra were gotten by reducing EL from whole emission spectra when the bias is above the threshold of EL. For different biases, no very obvious difference in the profiles of photoluminescent spectra from Ir(PPY)3 doped PVK. The relative intensity of PVK emission peak does not decrease while increasing the bias, which indicates the energy transfer rate from PVK to Ir(PPY)3 does not change with increasing bias. Both PL spectra in the prescence and absence of electric field are nearly the same but different from their EL spectra. For EL spectra, the emission from PVK host is hardly found. We can deduce that the main EL emissions don’t come from PVK chains to Ir(PPY)3 molecules which obey Fster energy transfer rule, but come from the recombination of injected carriers at Ir(PPY)3 molecules acting as both the carrier-trap and recombination centers.关键词：PVK;Ir(PPY)3;electric field modulated photoluminescence;electroluminescence99|76|4更新时间：2020-08-11
- 摘要：The preparations and optical spectra of Eu2+ ions doped-glass have been attracted much attentions due to their applications in optical devices such as Faraday rotators, lasers, high dense light storage and so on. In order to obtain more Eu2+ ions, many complex preparations have been done, for example under strong reductive atmosphere and so on. It is necessary to explore easy and simple method that can obtain glasses with high concentration of Eu2+. In the present paper, under air atmosphere Eu2O3 incorporated P2O5-BaO-Na2O-K2O glasses and Na2O-TeO2-ZnO glasses were prepared by melting at 1200℃. The emission spectra of Eu ions in the glasses were measured at room temperature. The structural and compositional effects on the valence-state of Eu ions were discussed. The results indicated that the Eu ions in the phosphate glass exist in the state of trivalent. However, some of the Eu ions in the Na2O-TeO2-ZnO glasses were divalent, although the glasses were prepared under air atmosphere. The Eu3+ ions could be effectively reduced to Eu2+ ions by the reductive action of silicon powder. Since the network of the tellurate glasses easily distorted and zinc oxide presented, Eu ions replaced the sites of the Zn2+ ions and the Eu2+ ions exist steadily in the glasses. The tellurate glasses containing overall Eu2+ ions with good optical property can be prepared by the proper melting processing and addition of silicon quantity.关键词：Eu2+ ion;P2O5-BaO-Na2O-K2O glasses;Na2O-TeO2-ZnO glasses;emission spectra123|45|1更新时间：2020-08-11
- 摘要：In recent years, Er3+-doped glasses with a broad 1.5 μm emission band have been extensively investigated for obtaining erbium-doped fiber amplifiers (EDFA) with a wide and flat gain spectrum in the telecommunication window, to be used in dense wavelength division multiplexing (DWDM) optical network systems. In this paper, Er3+-doped B2O3-SiO2-GD2O3-Na2O (BSGN) glasses were prepared by the technique of high-temperature melting at different temperature. The 1.5 μm emission spectra responsible to 4I13/2→4I15/2 transition of Er3+ at 17 Kand room temperature, absorption spectra, time resolved spectra and lifetime of the 4I13/2 state are measured and investigated, respectively. Both the bandwidth of the 1.5 μm emission and the J-O parameter Ω6 of Er3+ in the BSGN glasses increase with the increasing of B2O3 content, and their lifetime decreased. Abroad 1.5 μm emission band with bandwidth of more than 80 nm is obtained. The glass ceramics were obtained by the heat treatment for the previous glasses at different temperature above its glass transition temperature (Tg), they show different emission spectral shapes from the corresponding glasses. The measured time decay pattern of the 1.5 μm emission in the glass ceramic consists of a fast and a slow component, which are attributed to the glass phase and the crystalline phase, respectively, indicating higher 1.5 μm emission efficiency in crystalline phase than that in glass phase. Differential thermal analysis result (DTA) also demonstrates high thermal stability of the BSGN glasses. Crystallization by heat treatment is helpful to increasing emission efficiency of the 1.5 μm emission band. The Er3+-doped BSGN glasses are the promising materials for the EDFA in the 1.5 μm window of optical telecommunication system.关键词：gadolinium borosilicate glasses;Er3+;broadband emission110|71|0更新时间：2020-08-11
- 摘要：The glasses have some advantages over polycrystalline forms because it is easier to be fabricated into products with various shapes such as bulk plates and fibers. The glasses with long lasting phosphorescence phenomenon are worth investigating thoroughly not only for its conventional use as indicator or craftwork in darkness, but also on account of searching new optoelectronic materials or optical storage devices. In this article, a new long afterglow luminescent glass material was synthesized and reported. The long lasting phosphorescent glass with the composition (in mol%) of 40BaO-10B2O3-50SiO2:0.2Tb2O3 (BBST) was synthesized by the high temperature solid-state reaction at atmosphere ambient. The glass sample was characterized by the IR, UV-Vis absorption, fluorescence and thermoluminescence spectra, respectively. Bright green long lasting phosphorescence was observed in Tb3+-doped barium borosilicate glasses after the irradiation with a UV lamp (λmax=254 nm) for 30 min at room temperature. This green phosphorescence can be observed with naked eyes in the dark for up to 8 h after removing the UV lamp. The afterglow phosphorescence spectrum with dominant peak at 543 nm is almost identical with the emission spectrum of BBST glass sample in peak-position and shape. This indicates that the green phosphorescence originates from the characteristic emission of Tb3+. The peak at 543 nm of the phosphorescence spectrum is associated with 5D4→7F5 transition of Tb3+. The decay curve of the afterglow does not obey a simple exponential rule. The phosphorescence decays quickly at former 200 s and then decreases slowly in latter stage. The themoluminescence curve of BBST glass sample consists of five Gaussian-fitted components, which suggests that many kinds of traps exist in the glass matrix. The possible mechanism of the long lasting phosphorescence is suggested to be due to the recombination of electrons and holes at shallow traps in the glass matrix that can be thermally released at room temperature, and energy transfer between the recombination centers and Tb3+ ions.关键词：long lasting phosphorescence;glasses;Tb3+;traps108|125|2更新时间：2020-08-11
paper
- 摘要：Because ionized polyurethane-poly(ethylene glycol) copolymer(PUI) and poly[1,4-(2,5-bis(1,4,7-ethoxy) phenylene vinylene)-alt-1,4-(phenylene vinylene)](BETO-PPV) can be mixed well,we use PUI as polymer electrolyte and BETO-PPV as luminescent polymer to fabricate light-emitting electrochemical cell (SLEC). The device structure is identical to traditional LEC. The fabrication of SLEC and measurement of the electrical and electroluminescent characteristics were reported,and the experimental results were discussed by an electrodynamic model. Experiments and analyses show, because of congregate of cations,SLEC has a low turn-on voltage and Al can be employed as cathode as traditional LEC. Due to low density of immobile anions in PUI, steady-state current-voltage character depends on the height of the barrier for hole injection. So the curve of SLEC’s steady-state current-voltage character is imsymmetrical. In addition,the most important characteristic of SLEC is the fast light-emitting response. The response time of SLEC is about 10 ms, faster two orders of magnitude under a fixed bias than that of traditional LEC. By analyses of chemical character of BETO-PPV and PUI, it shows that oligo(ethylene oxide) side groups of BETO-PPV chains are stick to PUI chains so that the compound film of PUI and BETO-PPV forms a continuous network phase enabling fast ion transport. Another reason enabling fast ion transport is that a local ordered potential formed by fixed anions of SLEC forms less scatter for mobile cations than the disordered potential formed by mobile anions of traditional LEC. C-f characteristics conform SLEC’s fast time response.关键词：SLEC;response time;ion transport103|83|0更新时间：2020-08-11
- 摘要：The Er3+/Yb3+ codoped TeO2-WO3-ZnO (TWZ) glass samples with same doping concentration and different thickness were prepared. The absorption spectra, 1.5 μm emission spectra and fluorescence lifetimes of Er3+, excited by 970 nm, were measured. The absorption cross-section was calculated based on measured absorption spectra at room temperature. The emission cross-sections were calculated by McCumber theory. The effect of radiation trapping on the spectroscopic properties of Er3+ in TWZ glass was discussed. Because of the high refractive index of the glass and very large overlapping around 1.5 μm between the absorption cross section and the emission cross section of Er3+ in TWZ glass, the radiation trapping in the TWZ glass samples was very strong. The radiation trapping became stronger with the increase of the thickness of samples. Due to the effect of the radiation trapping, the measured fluorescence lifetime was longer than the calculated one, which caused the quantum efficiency large than 100%. The emission spectra were also broadened and the emission peak wavelength shifted to the longer wavelength slightly. When the sample thickness increased from 0.50 mm to 3.15 mm, the fluorescence lifetime increased from 2.60 ms to 3.10 ms and the quantum efficiency increased from 111% to 132%. At the same time, the fluorescence effective line width, Δλeff, increased from 76.2 nm to 91.7 nm and the emission intensity ratio of the main peak to the second peak, Is/Ip, also increased gradually. The fitting results showed that the Δλeff increased linearly with the increasing of the ratio value of Is/Ip. Based on the obtained linear equation for Δλeff and Is/Ip, the effective line width in the glass sample without the exis-tence of radiation trapping was deduced, which was 72.1 nm. The value was very close to the Δλeff calculated from the emission cross-section curve, which was 70.3 nm. So we suggested that the Δλeff calculated from the emission cross-section curve could be used to determine the Δλeff of Er3+ emission at 1.5 μm without the radiation trapping effect. For the first time, the opinion that the ratio of the Is/Ip to the σes/σep, or the difference between the Is/Ip and the σes/σep can be used to evaluate the radiation trapping of Er3+ at 1.5 μm band. Here the σes and the σep are the emission cross sections at wavelength of the second peak and the strongest peak, respectively, calculated by McCumber theory.关键词：erbium ions;radiation trapping effect;tungsten-tellurite glass;spectroscopic properties95|78|1更新时间：2020-08-11
- 摘要：Recently, because of the requirement of plasma display panels (PDPs) and a possible new generation of Hg-free lamps, much attention has been paid to phosphors for vacuum ultraviolet (VUV) excitation. BaMgAl10O17:Eu(BAM) is widely used as a blue emitting commercial phosphor for plasma display panels (PDP) and used in Hg-free lamp due to its high efficiency and good chromaticity. However, BAM suffers a thermal degradation during the manufacturing of PDP and a lifetime degradation during PDP operation. Thus the application of BAM in PDP is hindered. In Hg-free lamps, the degradation of BAM is mainly caused by thermal treatment during lamp manufacturing. One of the options to enhanced thermal stability and ion resis-tance for BAM is the application of a closed particle coating. Among the coating materials, MgF2 is preferable for its high secondary electron emission coefficient and low refractive index in the range from 130 nm to 7400 nm. In this work, a sol-gel process was applied to coat BAM phosphors with MgF2, which is low apparatus-dependent compared with other processes, using trifluoroacetic acid (TFA) and magnesium acetate as precursors. The coatings were characterized by XPS and SEM. Their anti-thermal degradation and photoluminescence properties were investigated under UV and VUV excitation. The results indicated that BAM phosphors were successfully coated with MgF2-coatings and the coated BAM was much more stable than the uncoated when both fired at 600℃ for 30 min in the air. The optimum anti-thermal degradation properties were obtained at the mass ratio 0.2% under 254 nm excitation and 0.5% under 147 nm excitation, respectively. As a conclusion, the sol-gel coating process is a promising method to protect the phosphor powders, and improves the phosphor’s anti-thermal degradation properties under UV and VUV excitation for application in displays and lamps.关键词：inorganic materials;thermal degradation;sol-gel process;coating;BaMgAl10O17：Eu109|57|5更新时间：2020-08-11
- 摘要：Many former researches discovered that SrO/Al2O3 ratio alteration in a bigger range would change the crystal phase composition of strontium aluminate doped by rare earth ions, and make crystals present different photoluminescence and persistent afterglow properties. However, the researches about the effect of SrO/Al2O3 ratio in a small range on luminescence of phosphor don’t systemically carry out up to now. In this paper, phosphor of Sr2AlO4:Eu,Dy, which has different SrO/Al2O3 ratio, is synthesized by solid-state reaction. The effect of SrO/Al2O3 ratio changed in a small range on phosphorescence of Sr2AlO4:Eu,Dy is studied. Experimental results show that the little alteration of SrO/Al2O3 ratio can’t cause the change of crystal phase composition of Sr2AlO4:Eu,Dy phosphor, but plays an important role in their photoluminescence and afterglow decay properties. The Al-rich phosphor has much better photoluminescence and longer afterglow life than that of Sr-rich phosphor. Emission spectra of the Sr2AlO4:Eu, Dy samples with different SrO/Al2O3 ratio tell that emission intensity increases with the decrease of SrO/Al2O3 ratio. Excitation spectra of the Sr2AlO4:Eu,Dy samples show that excitation intensity also increases with the decrease of SrO/Al2O3 ratio and excitation spectra have big change at the range of 220～250 nm with the changes of SrO/Al2O3 ratio. The appearance of new and intensive excitation peak at 220～250 nm when reducing SrO/Al2O3 ratio, suggests that new electron energy level is formed and new electron transition takes place after excitation. From afterglow decay results, it can be found that Sr-rich sample shows lower luminance and shorter persistent time. In order to further investigate the root reasons for above phenomena, thermal stimulated luminescence (TSL) spectra are measured and the results indicate that changing SrO/Al2O3 ratio will result in the changes of trap depth and trap density in the Sr2AlO4 crystal lattice: the more Al2O3, the bigger trap density and the lower trap depth. Based on above results and analysis of photoluminescence,afterglow decay and TSL, it can be concluded that in Sr-rich Sr2AlO4 crystal the chances for Eu2+,Dy3+ to replace the positions of Sr2+ is so slim that the density of luminescent central and traps in crystal lattice is very low. It is this reason that makes Sr-rich samples perform worse photoluminescence and afterglow decay properties.关键词：photoluminescence;afterglow;aluminate;trap94|49|3更新时间：2020-08-11
- 摘要：Thermoluminescence (TL) three-dimensional (3D) spectra of CaSO4 doped with Eu, and Ag, Mn were measured by 3D TL spectrometer. TL properties and mechanism of the CaSO4 phosphors were investigated. The glow peaks of Eu2+ at 385 nm, 120℃ and 154℃ are observed. The glow peaks of Eu3+ are found at 595, 620, 700 nm in several temperatures. The glow peak at 385 nm, 154℃ of Eu2+ is much stronger than that of Eu3+ emissions. It is found that annealing method can alter the concentration ratio between the Eu2+ and the Eu3+. The behavior of the Eu2+ and the Eu3+emission related to annealing temperatures is different. The intensity of the emission at 385 nm,154℃ of the Eu2+ is enhanced as annealing temperature increasing from 600℃, then passes a maximum at 900℃. However, the intensity of the emission of the Eu3+ ions is decreasing as increasing the temperature from 700℃. Dopant Ag is charge compensation impurity, which enhances the emissions of Eu3+ after co-doping Ag into CaSO4:Eu(0.1%). The glow peak of the Eu3+from 220℃ in the CaSO4:Eu shifts to 350℃ with enhanced intensity in CaSO4:Eu,Ag (0.1%,0.1%) while the glow peak at 385 nm, 154℃ of the Eu2+ are weakened and peak temperature is unchanged. Dopant Mn in CaSO4:Eu,Mn play not only a role of luminescence center, but also energy transfer which can transfer energy from the Mn2+ to the Eu2+ at 385 nm and 120℃. Therefore the glow peak of the Eu2+ (385 nm, 120℃) is intensified. The CaSO4:Eu,Mn prepared by present work is a good phosphor with high luminescence intensity. The results indicated that there are different TL mechanisms between the Eu2+ ions and the Eu3+ ions.关键词：CaSO4;Eu;TL spectra;luminescence mechanism137|80|0更新时间：2020-08-11
- 摘要：The high quality unintentionally doped Ga0.4In0.6As0.85P0.15quaternary semiconductor alloy, InPepilayers and distributed Bragg reflectors formed with Ga0.4In0.6As0.85P0.15/InPalternative layers have been grown on the S-doped high quality(100) InPsubstrates in an atmospheric or low pressure metal organic chemical vapor deposition system made up in our laboratory. The source materials are trimethylindium (TMIn), trimethylgallium(TMGa), arsine(AsH3) and phosphine(PH3). The growth temperature is 620℃ in the study. The pressure is 9.3×103 Pa in the reactor room. The lattice constant and composition parameters(x,y) were determined using double crystal X-ray diffraction and photoluminescence(PL) measurements. The lattice mismatch of the quaternary layers with the substrate was estimated to be less than 0.6%. The refractive index of Ga0.4-In0.6As0.85P0.15 and InPsemiconductor were measured. The distributed Bragg reflectors are formed by laying down alternating layers of Ga0.4In0.6As0.85P0.15 and InP with difference in refractive index. The function of the reflectivity of the DBR with different period number varied with wavelength and the period number of the DBR. According to the principle of the light through multiple-layer reflective films, the reflectivity of the DBR rapidly increased with the increasing of period number of DBR, when the center wavelength is 1.55 μm. The reflectivity of the DBR is greater than99.97%, as the period number of the DBR is 23. The experimental results have shown that we have successfully obtained the distributed Bragg reflectors, their period number are 3, 4, 7, 11, 15, 19 and 23, respectively. It is well-known that the existence of the immiscible region in the GaxIn1-x-As1-yPy/InP. The composition(x,y) of the GaxIn1-xAs1-yPy quaternary alloy is 0.4 and 0.15. They are in the region of immiscibility. It was found that the surface of the samples are grown in the region of immiscibility are rough rather than smooth. The interface quality between the GaxIn1-xAs1-yPy and InPwas effected. But the reflectivity of DBR with period number 23 is only 54.44%, much lower than the theoretical results.关键词：MOCVD;distributed Bragg reflectors;reflectivity94|64|0更新时间：2020-08-11
- 摘要：As well-known, ohmic contacts play a very important role in the fabrication of GaN-based devices. Recently, Au/Ni/p-GaNohmic contacts annealed in air or oxygen ambient have been studied extensively because of their low specific contact resistances and high transparency in the fabrication of GaN-based LED s. The roles of Ni, Au layers and their oxidation on the formation of p-GaN ohmic contact are still under dispute. Few works on the structure evolution in the oxidized Ni/Au contact were reported. Moreover, the difference between O2 and air for the oxidation ambient was not ascertained yet. In this work, thermal annealing in air and oxygen ambient with different time were performed on Ni/Au contact to p-GaN. The structural and electrical properties of the oxidized Ni/Au/p-GaN samples were investigated by synchrotron radiation X-ray diffraction (XRD). The GaNsamples used in our experiments were GaN-based LED grown by metalorganic chemical vapor deposition (MOCVD). p-type GaNlayer is about 200 nm thick. After Ni/Au(20 nm/40 nm) film was deposited by electron-beam deposition system, the samples annealed in oxygen or air for different time, 30,60,180,300 and 600 s respectively. 2θ and ω scans XRD of the samples were measured by the synchrotron radiation source. As a result, obvious NiOpeaks were detected by glancing incidence XRD in the annealing samples of Ni/Au contact to p-GaN. When the annealing time was changed from 0 to 600 s, the crystallinity of Au was improved. Apreferentially orientation of Au(111) paralleled with GaN [0001] was observed by ω scan (the rocking curve). It was believed that the Au went down to the interface and form the preferential orientation paralleling to GaN [0001] and the NiOwas reversed to the surface. It suggested that the Au, Ni, Oand Ga formed a kind of compound that is important to decrease the Schottky barrier. In the process, the dirty on interface was brought out to the surface, and maybe it could take some effect of lowering the Schottky barrier. It was observed that series resistance was reduced when the annealing time increased. The reduction of Au/Ni-p-GaN-Ni/Au series resistance meant the improvement of contact characteristics, which was related with the formation of the epitaxial Au and NiO. The formation speed of NiO annealed in oxygen ambient was faster than that annealed in air.关键词：GaN;ohmic contact;synchrotron radiation XRD112|71|0更新时间：2020-08-11
- 摘要：The intense visible photoluminescence (PL) of porous Si has attracted much interest as it opens up the possibility of fabricating light-emitting devices based on silicon technology. The effect was attributed to a quantum confinement of carriers in structures only a few nm in size, resulting in an effective increase of the apparent band-gap with respect to bulk Si. Recent years, it had been widely reported about Si and Ge nano particles embedded in SiO2 and Si3N4 films, some interesting phenomenon were also reported. Since the successful synthesis of amorphous semiconductor multiple films used plasma enhanced chemical vapour deposition (PECVD) by Exxon Corporation, the technology which need little complex epitaxy has attracted much attention, as we all known, the multiple films has a strong quantum effect, and also some interface effect would be magnified compared to the single layer films, it brings some novel phenomenon. The low temperature or room temperature photoluminescence had been widely reported, and they mostly concerned about the quantum effect and interface structure, but the photoluminescence dynamics of the multiple semiconductor films had not been reported. In this paper, we have performed multiple a-SiCx:H/a-Si:Hfilms successfully by PECVD. Microstructure and time-resolved PL spectra of the samples were studied. The results showed that a significant photoluminescence peak at about 650 nm was observed, and the peak position varies with annealing temperature. Amaximum intensity of PL peak and a minimum decay time (t1) were obtained for the sample annealed at 900℃. The origin of luminescence was suggested and discussed.关键词：a-SiCx：H/nc-Si multi-layers;PECVD;thermal annealing104|59|1更新时间：2020-08-11
- 摘要：Over the past few years, wide and direct band gap semiconductors have been intensively studied for their application as blue and ultraviolet light emitters. As a wide gap semiconductor, ZnO has a wide band gap (3.37 eV) and a large binding energy (60 meV). Therefore, ZnO is considered as one of the most promising candidates for short wavelength optoelectronics devices, and it is very important to conduct further studies of the properties of ZnO thin films. In this paper, indium-doped zinc oxides was prepared by radio frequency (rf) reactive co-sputtering on silicon (100) substrate at 430℃. Sputtering target were consist of metal zinc (99.99%) and metal indium (99%). Indium content is about 3% (the ratio of indium slices area to that of whole target) on the target. The sputtering gas is a mixture gas of argon (99.97%) and oxygen (99.95%), the partial pressure ratio of oxygen is 0.4. The structure, surfaces morphology, type of conductivity, electrical resistivity and PL spectra of the sample were characterized by X-ray diffractometer, scanning electron microscopy, hot probe, four-point probe and fluorescent spectrophotometer, respectively. There are four main ZnO diffraction peaks in the glancing angle X-ray diffraction patterns, and no diffraction peaks of In2O3 or Zn2In2O5 are observed. Therefore, we think that polycrystalline ZnO thin films was prepared by RF reactive co-sputtering. The θ-2θ scan mode X-ray diffraction patterns indicated that the film has highly c-axis orientation and low biaxial compressive stress (0.74 GPa). The 2θ angles of (002) diffraction peak is 34.48° and the full width at half maximum is 0.376°. The surface of the sample was smooth and flat. Compared with un-doped ZnO thin films, low resistivity (1.6 Ω·cm) n-type ZnO thin film was deposited on silicon (100) by doped indium. The blue-violet photoluminescence bi-peak located at 415 nm and at 433 nm is observed when exited with 340 nm wavelength in the photoluminescence (PL) spectrum at room temperature. In this paper, we think that the peak at 415 nm comes from In impurity defects and the peak at 433 nm originates from Zn interstitial defects.关键词：ZnO films;In-doped;photoluminescence spectra;rf reactive co-sputtering110|168|0更新时间：2020-08-11
- 摘要：The research of visible luminescence from silicon-based materials is very important in the optoelectronic applications. The indirect band gap structure of bulk silicon decreases the efficient light emission obviously. But in silicon nanostructures, optical transitions rates are very high. Because of quantum confinement effect, photoluminescence originated from silicon nanostructures can be observed. So the silicon nanostructures have received consi-derable attentions. Films of hydrogenated silicon nitride (SiNx:H) have been prepared by plasma enhanced chemical vapor deposition (PECVD) technique at low temperature. Strong room-temperature photoluminescence has been observed in the films annealed at low temperature (300℃). The analysis of XPS indicates the existence of the Si clusters in the silicon nitride films. From the IR spectra, for the annealed samples, there is a first decrease of the Si—Habsorption peak intensity followed by a increase when the annealing temperature is more than 700℃. When the annealing temperature reaches 900℃, the PL peak with respect to the Si dangling bonds disappears, and there is a significant blueshift of the intense PL peak from the Si clusters in the spectra. In terms of Raman scattering spectra, the size of the Si clusters has been calculated in order to illuminate the reason of the photoluminescence blueshift. In terms of all the results, the intense visible photoluminescence is attributed to the existence of the Si clusters embedded in the silicon nitride matrix.关键词：PECVD;photoluminescence;Si clusters;quantum confinement effect96|100|0更新时间：2020-08-11
- 摘要：Y2O3:Ho/Yb nanocrystals have been prepared by combustion method. The nano-crystals size was estimated by X-ray diffraction. Green emissions near 549 nm and red emissions near 668 nm were observed under 488 nm and 980 nm excitation, which were associated with 5S2(5F4)→5I8 and 5F5→5I8 transitions of Ho3+ that required two-step energy transfer (ET) from Yb3+ ions. The intensity ratio of red light to green light varied obviously with the nanocrystals size, which should be due to surface defects. The smaller the size was, the weaker the emission intensity became. As the same time, the ratio of red light intensity to green light intensity increased obviously with the decrease of particle size. As the particle size decreased, a great number of surface defects were involved. These defects, which acted as nonradiative transition channels, led the decrease of the emission intensity. On the other hand, the surface of the powders absorbed the CO2 and the H2Oin the air. So large vibrational modes could be produced, which offered the probability for depopulating of the excited states nonradiatively. Thus, the nonradiative relaxation rates from 5S2(5F4) to 5F5 became much faster. As a result the ratio of red light intensity to green light intensity decreased. Two nonradiative relaxations processes, 5S2(5F4)→5F5 and 5I6→5I7, are involved in upconversion luminescence, but only 5S2(5F4)→5F5 in downconversion. So the increase of emission intensity ratio is more prominent in upconversion luminescence than downconversion luminescence.119|189|4更新时间：2020-08-11
- 摘要：The nanopowders of Y2O3:Eu3+ with different co-dopants (Li+, Na+, K+, Mg2+, Sr2+, Ba2+, B3+ and Al3+) were prepared by glycine-nitrate solution combustion synthesis. Structure and luminescent properties, such as the location of charge transfer band (CT band), fluorescent intensity and lifetime of 5D0→7F2, were studied and compared each other. The detail contents were discussed as follows: 1. The nanocrystalline Y2O3 were cubic in symmetry by X-ray powder diffraction (XRD) pattern. The average particle sizes estimated by Scherrer’s equation indicated that co-dopants could finely adjust the average particle size. That is, co-doping of Mg2+ and Al3+ ions decreased the combustion temperature, as a result that the size of the particles decreased. However, co-doping of Li+, Na+ and K+ increased the combustion temperature and the particles’size. 2. The excitation and emission spectra were measured. Compared to undoped particles, the charger transfer (CT) band exhibited blueshift in most of doped ones. For Li+-doped particles, the shift was 6 nm. The emission intensity varied strongly with co-dopants. Li+-, Na+-, K+-and Sr2+-doped powders had stronger brightness than undoped ones, B3+-and Ba2+-doped powders had no obvious intensity change, but Mg2+-and Al3+-doped powders had weaker brightness. 3. The high-resolution emission spectra were recorded under the 266 nm laser excitation. Abroader band appeared between610 and 631 nm, which was attributed to amorphous phase. The results indicated that the co-dopants of Li+, Na+, and K+ can promote the crystallinity of the samples. However, the co-doping of Mg2+ and Al3+ drastically causes the structure disorder. 4. The fluorescence decay curves of 5D0 of the samples were measured under the excitation of 266 nm laser. The lifetime of particles co-doped with Li+ and Na+ increased as compared to that of undoped one. However, the lifetime decreased as co-doped with other dopants. In a word, the luminescent properties, such as the location of charge transfer band (CT band), the fluorescent intensity and lifetime of 5D0→7F2, varied with co-dopants. It can be concluded that the variation depended on co-doping by modifying the size and crystallinity of nanoparticles. And the dependence was more strongly on the crystallinity than the particle size.关键词：nanocrystalline Y2O3：Eu3+;crystallinity;charge transfer band;surface defects100|81|4更新时间：2020-08-11
- 摘要：The nano-crystalline silicon carbide films were grown by hot filament chemical vapor deposition (HFCVD) technique with CH4 and SiH4 as reaction gases. To reduce the large lattice mismatch between SiC and silicon, a buffer layer was made by carbonizing the surface of the Si substrate in the HFCVD system. An optimum condition for the buffer layer was determined. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) were employed to analyze the composition and the structure of the films. The results from these techniques showed that the films deposited at relatively low temperature were nano-crystalline SiC, with an average dimension of about 60 nm. The visible-light emitting in the wavelength range from 380 nm to 420 nm had been observed from the nano-crystalline films excited by 325 nm He-Cd laser at room temperature in photoluminescence experiments. In the other side, we had analyzed and studied the variation of photoluminescence (PL) spectra with carbonized time. It was showed that the nano-crystalline SiC were obtained with carbonized time of 10 min on Si substrate for a buffer layer prepared by carbonization.关键词：nanocrystalline materials;SiC;photoluminescence;carbonized;HFCVD121|66|1更新时间：2020-08-11
- 摘要：As a substrate, because of their relatively regular structure with narrow size distributions of pore diameters and interpore spacings, porous alumina membranes are used to make compactly integrate with samples, and don’t affect the photoluminescence (PL), so we select it as a substrate to grow nano-crystalline Si (nc-Si) films and study the temperature dependence of independent PL. In this paper, nc-Si films have been fabricated using high vacuum electron beam evaporation on porous alumina. Except PL of samples at different temperature, several measuremental techniques, including scanning electronic microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared absorption (FTIR) were used to analyze the morphology characteristic, crystalline phase and composition of the nc-Si films. After the processes of high temperature annealing at 650℃, a sharp diffractional peak of sample at 28.5° may be detected by XRD, it is demonstrated that the samples have a few crystalline silicon. FTIR measurements show that there are oxygen and hydrogen in nc-Si films. The PL spectra of nc-Si films were observed in the temperature range of 10～300 K. The experimental results of PL show that the change of PL peak and intensity of nc-Si films is dependent on measurement temperature. With temperature increasing from 10 K, the PL peaks have a red shift, while they have a peculiar blue shift in range of 50～80 K. The PL intensity decrease with temperature increase, while they have a little abnormal increment in the range of 60～80 K. In order to get the right reason, we must think over the systhetic effect of quantum confinement and surface state to analyze the PL mechanism of nc-Si films. According to previous theories, it has been suggested that the photoluminescence originated from the quantum confinement effects and the luminescent centers in surface layers covering the nanoscale silicon particles.关键词：nano-crystalline silicon;photoluminescence;quantum confinement-luminescence center89|107|0更新时间：2020-08-11
- 摘要：Since the discovery of light emitting diodes based on PPV in 1990, PPV and its derivatives have been investigated widely with experiments or theories due to their electroluminescence properties, but the excited state and the interchain species of them remain controversial. To study the nature of the interchain species, the optical properties of the isolated MEH-PPV chains in the dilute solutions are investigated. It has been found that the fluorescence of conjugated polymers is heavily influenced by the conformations of the polymer chains. The polymer chains become more tightly coiled in the poor solvent to make more conjugated segments aggregated and then to form more interchain excitons under photoexcitation. With increasing the proportions of the poor solvent in the dilute solutions, the intensities of the highest PL peaks (P1) (emission from intrachain excitons) are reduced due to the increase of conformational defects in the polymer chains, and the relative intensities of the peaks at about 590 nm (P2) (emission from interchain excitons) are increased. From the absorption and photoexcitation spectra of the dilute solutions, it can be found that the intensities of absorption peaks and photoexcitation at long wavelength are increased with increasing the proportions of the poor solvent in the dilute solutions. By analyzing the absorption and the luminescence spectra of MEH-PPV dilute solutions, it can be concluded reasonably that the formation processes of interchain exciton are dependent on the photoexci-tation energies. For hν>Ea, a majority of intrachain excitons are relaxed by radiative recombination, but a few of intrachain excitons can be transferred to the aggregated segments along the polymer chains, then π electrons are delocalized over the aggregated segments to form interchain excitons. In other words, interchain excitons have same photoexcitation process as intrachain excitons. For hν<Ea, the aggregated segments in the single chain can absorb photon energies to form interchain excitons.关键词：conjugated polymers;photoluminescence;intrachain exciton;interchain exciton94|90|1更新时间：2020-08-11
- 摘要：The MCP ion barrier film in low-level-light imaging tube and its process techniques were introduced. The electron and ion transmittance of this film was studied. The concept of dead voltage of MCP with film was discussed. The dead voltage curve, and the relation between dead voltage and thickness of film were tested. The results of performance testing comparisons were presented. The composition of film was analyzed by XPS. Through theoretical analysis on ion transmittance characteristics for MCP ion barrier film, we proposed the concept characterized the inhibition ability of film from ion transmitting, testing theorem and related techniques for ion transmittance measuring.关键词：microchannel plates;ion barrier film;without pollution film forming process;dead voltage;ion transmittance104|66|0更新时间：2020-08-11
- 摘要：Carbon nanotubes(CNTs) have attracted much attention because of their unique structure and properties since their discovery. One important potential application for the CNTs is as electron field emission sources in cold cathode flat panel displays as electron guns. Although a few of studies on the field emission properties of patterned aligned multi-wall nanotubes (MWNTs) were reported, the catalyst films were patterned by conventional photolithography and etching techniques. This method is too troublesome in application. In this paper, we prepared CNT patterns by a simple method, which is based on laser writing technology. Carbon nanotubes (CNTs) films were grown on patterned Ni lines coated substrate by microwave plasma chemical vapour deposition (MWPCVD). Ni films deposited on ceramics substrates by d.c. magnetron sputtering are used as catalysts for growing the CNTs. The ceramics substrates were mechanically polished using various grinding and polishing powders in order to uniform Ni film. Before growing CNTs, the Ni films were patterned to be lines by laser writing technology and then the CNTs were deposited on the catalyst patterns. The source gas for growing the CNTs was a mixture of H2 and CH4. The gas flow rate of H2 is 100 sccm, and the growth pressure was 6.5×103 Pa, various deposition times were applied to control the length of the carbon nanotubes. Scanning electron microscopy (SEM) was used to determine the morphology of carbon nanotubes. Raman spectroscopy was used to analyze the structure of carbon nanotubes. The field emission characteristics of the samples were measured by using a diode structure. The transparent anode was made of coating phosphor onto an ITO coated glass plate. The CNTsamples as the cathode were separated from the anode by a mica sheet with a suitable hole as the emission area. The gap between the anode and the cathode was 500 μm. The measurement was conducted under pressure of 3.6×10-5 Pa. By varying process conditions such as Ni layer thickness, gas flow rate, deposition time, reactive temperature, the optimum conditions for field electron emission were found. When gas flow rate of CH4 was 5 sccm, Ni film thickness was 150 nm, deposition time was 5 min, and reactive temperature was 700～800℃, the field emission properties are best. At this condition, all nanotubes are well aligned as characterized by SEM. Turn-on field of 1.3 V/μm, emission current density of 6.8 mA/cm2 and field enhancement factor of 8477 were achieved.关键词：carbon nanotubes (CNTs);MWPCVD;field electron emission;Raman spectrum91|67|1更新时间：2020-08-11
- Address：No.3888 Dong Nanhu Road, Changchun, Jilin, China Postal code：130033
- Tel：0431-86176862 Email：fgxbt@126.com
- Technical support is provided by Beijing Founder electronics co., LTD 吉ICP备11002662号-17
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0