最新刊期
卷 28 ， 期 2 ， 2007
- 摘要：The properties of the weak-coupling bound polaron in quantum well are studied using the linear combination operator and the unitary transformation method. The relations of the ground-state energy of the bound polaron in quantum well with the Coulomb bound potential, the vibration frequency, magnetic field and the well-width are derived. At the same time, the dependency of the vibration frequency on the Coulomb bound potential and magnetic field is discussed. The results of numerical calculation show that the ground-state energy changes with the Coulomb bound potential, magnetic field and the well-width, which will increase with increasing magnetic field and decrease with increasing the Coulomb bound potential and the well-width. The vibration frequency will increase with increasing the Coulomb bound potential and magnetic field.关键词：quantum well;bound polaron;ground-state energy;linear combination operator;magnetic field100|271|3更新时间：2020-08-11
- 摘要：With the use of linear combination operator and the variational methods of Pekar type, the properties of the weak-and strong-coupling polarons excited state in parabolic quantum wires were studied. The ground state energy, the first internal excited energy and excited energy were calculated. Their dependence on the confinement strength of parabolic quantum wires was depicted. Numerical calculation indicated that the ground state energy, the first internal excited energy and the excited energy of the weak-and strong-coupling polaron in a parabolic quantum wire will increase with increasing of confinement strength, respectively.关键词：quantum wire;polaron;ground state energy;the first internal excited energy;excited energy120|101|7更新时间：2020-08-11
- 摘要：With the quick development of the semiconductor growth technology, people have produced kinds of quantum dots. Due to the novel optoelectronic properties and the transport characteristics of quantum dots, there will be a widely applied prospect for them. In recent years, the physical characteristic of a bound polaron in a quantum dot has been of considerable interest. Many investigators studied the properties of the bound polaron in a quantum dot by means of various theoretical and experimental methods. Recently, the properties of bound polaron in quantum dot were studied by using a linear combination operator method by the presents. However, the properties of the excited state of the bound polaron in a quantum dot have not been investigated so far. In this paper, the properties of the excited state of the weak-coupling bound polaron in a quantum dot were studied by using a linear combination operator and unitary transformation method.The relations of the vibrational frequency of the weak coupling bound polaron in a quantum dot with the effective confinement length of the quantum dot and the Coulomb bound potential are derived. Relation of the first internal excited state energy, the excitation energy and resonance frequency of the weak-coupling bound polaron in a quantum dot with effective confinement length of quantum dot, the electron-phonon coupling strength and the Coulomb bound potential are calculated. The numerical results show that the vibrational frequency, the first internal excited state energy, the excitation energy and the resonance frequency of the weak-coupling bound polaron in a quantum dot will increase strongly with decreasing the effective confinement length of the quantum dot and increase with increasing the Coulomb bound potential. The first internal excited state energy will increase with decreasing the electron-phonon coupling strength.关键词：quantum dot;bound polaron;linear combination operator;excited state98|101|0更新时间：2020-08-11
- 摘要：A new kind of bisazo(BA1) was synthesized as a material candidate for perpetual information storage application. When the sample was pumped by the beam of 532 nm, almost half of the BA1 molecules undergo a reversible trans-trans to cis-cis isomerization in the polymer matrix, resulting in photo-induced birefringence. Hence, the dependences of photo-induced birefringence and the transmission signals on the pumping beam intensities in BA1 doped poly (methyl methacrylate) (PMMA) film were studied. It is shown that transmission signals increase with the enhancement of pump beam intensities. Here the two linear polarized beams with parallel state (SS) and orthogonal state (SP) were used to investigate holographic storage. It can be clearly seen that the diffraction efficiency of SP grating much higher than that of SS configuration.关键词：photo-induced birefringence;polarization holography;BA1;He-Nelaser128|81|1更新时间：2020-08-11
- 摘要：Marine luminous bacteria, heterotrophic bacteria give out visible light in normal physiological condition. Many study results show that the luminescence mechanisms of variety luminous bacteria are the same. The light-emitting in bacteria involves the oxidation of reduced riboflavin phosphate (FMNH2) and a long-chain fatty aldehyde with the emission of blue-green light. The enzymes that catalyze the bioluminescence reaction in these organisms are called luciferases, and in most cases the substrates are designated as luciferins. However, consistent with the apparent absence of strong evolutionary relationship between many of the light-emitting systems, significant differences exist between the bioluminescence reactions as well as the structures of the luciferases (enzymes) and luciferins (substrates) from different organisms. The luminescent characte-ristics of marine luminous bacteria connect with material structure in the bacteria, marine environment elements and pollutants in the seawater etc, the connect study includes that spectrum property, light-emitting intensity, light-emitting characteristic parameter, light-emitting conditions and the structure of luciferases from different luminous bacteria. Thorough understanding these properties of marine luminous bacteria and carrying out the study of application can supply effective methods for the application of the property of marine luminous bacteria, and promote comprehensive researches on ocean biology, ocean optics and biochemistry, and show the feasibility of physics researches on marine luminous bacteria. And the predictions show the concentration and toxicity of pollutants in the water is determined by luminescent intensity of luminous bacteria, the submarine sailing exits the whirlpool and the luminescent bacteria bioluminescent makes the whirlpool to be a ray track which can be used to detect submarine, the luminescent characteristics can also be used to improve in the under water light communications and exploring, ocean water color remote sensing, bacterial classification bioluminescent immunity and antibiotic concentration determination etc. In this article, important significance of the study on luminescent characteristic of marine luminous bacteria was clarified and reference is given for further developing.关键词：marine luminous bacteria;luminescent characteristic;application study173|109|3更新时间：2020-08-11
- 摘要：Microcavity structure consisting of distributed Bragg reflector and metal silver mirror is designed. The structure is glass/DBR/ITO/TPD/Alq3/Ag.The tris(8-hydroxyquinoline) aluminum(Alq3) is the electron transport layer and the emissive layer, and the N,N-diphenyl-N,N-bis(3-methyl-phenyl)-1,1′biphenyl-4,4′diamine(TPD) is the hole-transport layer. Compared to the electroluminescence(EL) spectra of non-cavity OLEDs, the linewidth of the MOLEDs is narrower, and the emission peak is enhanced. So the microcavity effect is very observable. In this work, the matrix method was adopted.The dependence of the electroluminescence(EL) spectra on the cavity length,the emitting layer thickness, the position of the interface between EML and HTL and the position of the emission region was analysed detailedly. In all calculation, the thickness and refraction of ITO and the thickness of the metal silver were kept constant. The results show: 1.with increasing the thickness of cavity, the normalized electroluminescence(EL)intensity decreased continually; 2.with increasing the thickness of the emitting layer, the normalized EL intensity discontinuously changed; 3.because the electron mobility in Alq3 is different from the hole mobility in TPD, the emitted radiation was strongly dependent on the position of the emissive layer inside the cavity. Finally, the emission region should be narrow at the center of the electric field in the resonant cavity to optimize MOLED.关键词：microcavity organic light-emitting device;distributed Bragg reflector;electroluminescence(EL)113|493|4更新时间：2020-08-11
- 摘要：Organic/polymeric electroluminescence (EL) has attracted much attention because of their potential applications in larger-area full-color flat-panel displays. Since the first high efficient organic light emitting diode (OLED), which used the aromatic diamine as the hole transport layer and tris(8-hydroxyquinoline) aluminum (Alq3) as the electron transport/emission layer, was demonstrated by C. W. Tang in 1987, Alq3 is commonly used as the electron transport and/or emitting layer in OLEDs for its high fluorescent efficiency, high crystallizing temperature and stable performance. Recently, in order to get higher efficient and stable devices, many efforts have been made on the synthesis of high luminescence efficient materials, such as ZnqCl2 have been synthesized and also its light-emitting devices were prepared by P. Y. Liu etc. Methods of calculation quantum chemistry are effective tools for studying the mechanism of photostimulated luminescence materials. To our knowledge, up to the present, there has not been any theoretical report on the spectrum of ZnqCl2. In this paper, two derivatives of ZnqCl2 (MqCl2, M=Mg, Be) are designed, and the structures of MqCl2(M=Zn, Mg,Be) and Znq2 were optimized in the ground states using ab initio HF and B3LYP methods. At the same time, the molecular structures of the first singlet excited state for ZnqCl2 and its derivatives were optimized by CIS/6-31G(d). The absorption and excite spectra based on the above structures were obtained by the time-dependent density functional theory (TD-DFT) by the B3LYP method with the 6-31G(d) basis set. The calculated results of luminescence originate from the electronic transition from the hydroxphenol ring to the pyridine ring. The calculated results of emission spectrum for ZnqCl2 and its derivatives have good agreement with the experimental data. All compounds (MqCl2, M=Zn,Mg,Be) are excellent electrontransporting materials,the luminescence peak wavelength of them can be tuned little by different metals on the ligand 8-hydroxyquinolinateo anion.关键词：bis(8-hydroxyquinolinolinato)zinc derivative;electron spectrum;excited state;TD-DFT93|65|1更新时间：2020-08-11
- 摘要：Organic light-emitting diode (OLED) has attracted considerable attention due to their unique image quality and market potentials in display field. Efficient blue, green and red emitters with excellent color purity are required for full-color display application, so far great improvements have been achieved for the life time and efficiency of the red and green materials. However, the blue emitting material is still a barrier to commercial applications of OLEDs.Using vacuum thermal evaporation method, blue OLEDs were fabricated by inserting a bathocuproine (BCP) as hole blocking layer (HBL) into conventional double layer (DL) device at the interface of N,N-bis-(1-naphthyl)-N,N-biphenyl-1,1-biphenyl-4,4-diamine (NPB)/8-hydroxyquinoline aluminum (Alq3). Device structure is indium tin oxide (ITO)/NPB/BCP/Alq/Mg:Ag, where NPB acts as both hole transporting layer (HTL) and emitting layer (EML), and Alq3 as electron transport layer (ETL). The active emissive area of each device defined by the overlap of ITO and Mg:Ag was 4mm×4mm. Measurements of luminance-voltage (L-V) and current density-voltage (J-V) characteristics were carried out with a Keithley 4200 Semiconductor Characterization System, photoluminescence (PL) and electroluminescence (EL) spectra were measured with an OPT-2000 system. The luminance-voltage and current density-voltage characteristics of devices were investigated, and dif-ferences between their performances were discussed. The results demonstrate that the maximum luminance and luminance efficiency of the BCP device are 2900 cd/m2 and 0.55 lm/W, respectively. The peak of electroluminescence (EL) spectrum locates at 445nm and the Commissions Internationale d′Eclairage (CIE) coordinates are (x=0.16, y=0.09), which are independent on the variation of bias voltage. Energy level diagrams were employed to analyze the diversity of device performance with different structures. We find that the high EL performance of the BCP device is attributed to better balance of carriers in the NPB layer by inserting BCP as hole blocking layer (HBL). Optimization of device structure and performance, via adjusting thickness of organic layers, is under investigation.关键词：organic light-emitting diodes;NPB;BCP;blue light136|60|1更新时间：2020-08-11
- 摘要：By adjusting thickness and luminous place of the luminous DPVBi layer in the same laboratory conditions, organic light-emitting devices have been produced. We designed different device structures and have produced a luminous device in the experiment. Firstly, we designed a group of devices with same structures perfectly, except different DPVBi layer thickness, as a result, their spectrum changed. When DPVBi layer thickness was 5 nm yellow-light was emitted.When DPVBi layer thickness was 10nm white-light was emitted because blue and yellow light were emitted symmetrically. With increase gradually of DPVBi layer thickness, ingredient of bluelight was increasing, and the emission color of the devices transferred little by little into blue. As a result, the emission hue of device changed due to different thickness of DPVBi layer. Secondly, DPVBi layer was laid on the different places in the device, the luminous performance of the device was different. From the experiment we can see that the DPVBi layer in different place had the different luminous essences: the luminous DPVBi layer before rubrene emitted blue light as a light-emitting layer;but the luminous DPVBi layer after rubrene didn't emitted light. According to compare of HOMO and LUMO energy grade used in the materials, the luminous DPVBi layer after rubrene performed an function of hole block only. This would affect the luminous brightness and efficiency of the organic light-emitting devices to a large extent. If by adjusting reasonably thickness and luminous place of the luminous DPVBi layer, the light hue of devices may be adjusted to gain colors expected. On the other hand, white-light devices were expected to produce, which was significant.关键词：organic light-emitting devices;luminous layer thickness and location;performance of devices109|109|4更新时间：2020-08-11
- 摘要：Studies and applications of organic light emitting display (OLED) have indicated that it is one of the promising technologies of planar display. Metaloquinolates with high stability and high fluorescence quantum efficiency are widely applied in organic EL devices. The experimental and theoretical investigations of these complexes have been widely implemented, while the theoretical study of Liq attracted little attention. The singles configuration interaction (CIS )and the time-dependent density functional theory (TD-DFT) are main methods for theoretical study on molecular excited state and electronic spectrum. In this paper, the frontier molecular orbit and electronic spectrum of Liq and its derivates are calculated by CIS and TD-DFT method. The effect of substituting group on the frontier molecular orbit and the electronic spectrum were analyzed. All this will provide a theoretical basis for the molecular structure design of organic electroluminescent materials. We designed 18 kinds of derivates which were obtained by substitution of three kinds electron-withdrawing group (C6H5,CN or Cl) at different position, respectively. The derivates of 8-hydroxyquioline lithium (Liq) were investigated quantitatively by means of DFT/B3LYP. The most stable substituted derivates (2-C6H5-Liq, 5-CN-Liq and 6-Cl-Liq) were selected according to the lowest energy rule. Basing on that, the absorption spectrum is calculated by TD-DFT, and the structures of excited states were optimized by CIS method. On the optimized-structures of excited states, the emission wavelength was predicted by TD method. And then the effect of substituting group on the frontier molecular orbit and electronic spectrum were discussed. The results indicated that the electronic withdrawing group affected mainly the electron cloud distribution of the frontier molecular orbit, which was correlated to the electronic withdrawing ability of ligand. The electron-withdrawing group on phenoy ring makes the HOMO-LUMO band gap increased. The increase of band gap then leads to a blue shift of electronic spectrum. Substitute position was related to electronic spectrum shift. The electron-withdrawing group on pyriding ring makes the HOMO-LUMO band gap decreased. The decrease of band gap then leads to a red shift of electronic spectrum. The simulative peaks at 269.94, 373.26 nm of the UV absorption spectra and the peak at 461.7 nm of emission spectra of Liq are closed to the peaks at 259.8, 363.8 nm of the experimental UV absorption spectra and the peak at 452 nm of emission spectra of Liq. It indicates that the TD-DFT method do well in predicting the electronic spectrum of metaloquinolates.关键词：8-hydroxygquinoline lithium;electronic withdrawing group;electronic spectrum;the frontier molecular orbit;TD-DFT105|86|1更新时间：2020-08-11
- 摘要：Since Tang reported their first double-layer green thin-film organic electroluminescent device with high efficiency and low driving voltage, organic light-emitting diode (OLED) displays have led to intense activity around the world for this new display technology due to its lots f promised advantages over existent display technologies. Most research and development has expanded to the device emitting mechanisms and new organic materials but several researches on the OLEDs fabrication process. Since OLEDs are the sandwich structures of one or several organic materials between two electrodes, they can be integrated in a passive matrix (PM) addressed display by patterning the anode in columns and the cathode in rows. The key process of PMOLED substrate is the fabricating cathode separator pattern by photolithography process.The image reverse technique for substrate separator includes coating, pre-baking, exposing with photomask, reverse baking, and flood exposing. The photoresist (PR) AZ5214 was coated on glass substrate with etched ITO film patterns by Delta30bm coating machine, and then pre-baked by Delta300bm. The photolithograph machine is Karl-Suss MA6. At last the substrates with cathode separator pattern were used to fabricate organic device to test the separator performance.When PR were uniformly exposed under UV light, strong optical absorption by the photo active compound (PAC) in the PR films, and as the PAC is destroyed, this absorption is removed as well, so the upper layer PR is exposed before the bottom layer. The development of photoresist can be considered a surface-rate limited etching reaction. The parameters that control this rate are resist and developer chemistry (held constant) and the PAC concentration of the photoresist at the surface exposed to the developer. The exposing model and developing model can be connected by PAC concentration and the shape of developed PR can be simulated.The main factors effecting reverse taper shape were thickness of photo-resistance, exposure and reversal bake. SEM test shows the reverse trapeziform shape of separator section with 45°obliquity and photoresist thickness 3μm. Optimum parameters about preparation cathode separator were obtained, coating rotation speed 1200r/min, pre-bake 100℃/90s, exposure time 0.8s, reversal bake 125℃/45s, flood exposure time 5.5s, developing time 40s.关键词：OLED;cathode separator;image reverse;photolithography;reverse trapeziform shape146|411|1更新时间：2020-08-11
- 摘要：Top-gate all organic thin-film field-effect transistors are fabricated one-off by fully-evaporation method without breaking vacuum,which has many advantages. The fabrication technology simplifies the device processing, and avoids the spot due to the preparation condition change. By evaporation method preparing device, the every layer film thickness can be controlled rigorous, and the thinner, symmetrical, compact film layers are propitious to reduce the operation voltage and enhance the device on-current. The source-drain electrode can be prepared by conventional photolighography technique on the ITO coated glass substrates, and the active layer, insulator layer and gate electrode can be patterned by different shadow masks, which are propitious to scale down device dimension and enhance integration degree. When the OTFTs with topgate were used to integrated circuit or active-matrix OLED display, the above advantages will be more clearly. All-organic thin-film field-effect transistors (Device A) with pentacene/thin Teflon insulator film of 100 nm were successful fabricated, with operating voltage reach to 40V, threshold voltage VT=-8V and mobility μ=1.0×10-2cm2/V·s. As for Device B, with the thickness of Teflon insulator film decrease to 50 nm and the same process condition with that of Device A, the operating voltage fell to 10V, threshold voltage VT=-3Vand mobility μ=1.2×10-2cm2/V·s. The result indicates that thinner insulator film can reduce operation voltage observably. However, the mobility has no obvious change with the similar pentacene/Teflon interface performance due to the same process condition. When the OTFT (Device C) fabricated with PMMA (150nm) replacing Teflon as insulator layer, the threshold voltage of device was decreased to near 0V, and mobility was increased more 3 times than that of the previous devices, and the saturation current was also increased obviously. These results indicate that the appropriate organic insulator can be used to improve the interface performance of active layer/insulator layer interface, and improve the device mobility.关键词：fully-evaporation;all-organic thin-film field-effect transistors158|63|0更新时间：2020-08-11
- 摘要：The most characteristic of solid state reaction at low temperature is that reaction is in progress at room temperature or near room temperature. Compare with liquid state reaction, solid state reaction is high selection and high yield. Because solid state reaction don’t need solvent,and this is environtly friendly, so it is a green synthesis method. A lot of people are interested in it recently.We have synthesized four solid complexes of rare earth with phenylacetic acid (L) by method of solid state reaction at low temperature. Elemental analysis, rare earth coordination titration, Molar conductivity studies suggest that the composition of the complexes is RE(L)3·nH2O(n=0.5～1.5;RE=La,Nd,Eu,Tb;L= C6H5CH2COO-).TGA curve of La3+ complex began to lose weight at 65.41～86.03℃ and weight loss was 1.835%, which was good accordance with the theoretical data 1.628% when complex had 0.5 water molecular. The temperature of losing water was lower, so water is induced to be crystal water. At 345.78～376.52 ℃ there is a great lose weight which was caused by the decomposition of La3+ complex.The IR spectra of sodium salt of the ligand show bands at 1571cm-1(s) and 1386cm-1(s),assigned to carboxyl group’s antisymmerty stretch vibration νas(COO-) and symmetry stretch vibration νs(COO-). In addition, the band at 3 026,1 491,706cm-1 are individaully assigned to phenyl’sνC—H,νC—C,δC—Hvibration. The IR spectra of complexes shows bands at nearby 1546～1553cm-1(s) assigned to νas(COO-) with a shift of 18～25cm-1 to the lower frequency region,which compared with sodium salt of ligand; The band at nearby 1393～1403 cm-1(s) is assigned to νs(COO-) with a shift of 7～17cm-1 to the higher frequency region, which still compared with sodium salt of ligand.These results indicate that the carboxyl group is bonded to the metal ions through two oxygen atoms as a symmetrical chelating bidentate group.The 1H NMR of the ligand in DMSO shows the proton of phenyl resonance is multiplet peaks at (7.22~7.33)×10-6, and integral intensity shows it has five protons; The proton of methylene group resonance peak is at 3.56×10-6, and integral intensity shows it has two protons. The proton resonance of the —COOH is at 12.33×10-6. The 1H NMR spectra of the complexes are similar. The proton of phenyl and methylene group resonance peaks are all clearly,and all shift to high field at different degree. The result indicated the carboxyl group’s oxygen of ligand coordinated with metal ions, which produced the shielded effect,it led to the proton resonance peaks shifting to high field. The absence of the —COOH proton resonance indicates that the carboxyl group is bonded to the metal ions through COO-group.Fluorescence spectra of Eu3+ complex show main emission peaks at 592.2 nm and 614.0 nm, which correspond to magnetic dipole transition 5D0→7F1 and 5D0→7F2 electric dipole transition of Eu3+ ion, respectively. The intensity ratio of the latter to the former is 2.1. It indicates that there is no inversion symmetry at the site of Eu3+ ion[10]. Fluorescence of complexes of Eu3+ with phenylacetic acid is part of M→M and L→M mixed luminescence.Fluorescence spectra of Tb3+ complex show main emission peaks at 546.0 nm, which correspond to 5D4→7F5 transition, respectively. The emission intensity is 459.5 a.u. Fluorescence of complexes of Tb3+ with phenylacetic acid is part of L→M luminescence, and emission intensity is stronger than Eu3+ complex. The ligand has sensitized Tb3+ ion in fluorescence intensity.关键词：rare earth complex;phenylacetic acid;solid state reaction at low temperature;luminescence;shape analysis106|62|1更新时间：2020-08-11
- 摘要：Eu3+-doped oxyphosphate (La3PO7) nanoparticles were synthesized by a straightforward combustion method. The synthesis procedure is similar to that of preparing oxide nanomaterials by the combustion method, but here (NH4)2HPO4 is used in producing phosphate nanoparticles. Firstly, La(NO3)3 was prepared by putting appropriate molar rate La2O3 (1.5mmol) and Eu2O3 into the thin HNO3, stirring to a transparent solution. Excess water was evaporated and made it condensed while heating to obtain the solid La(NO3)3. Then, put into 10mL thin HNO3. At the same time, 0.1321g (NH4)2HPO4 and 0.2703g Glycine were dissolved in deioned water (10mL). Thirdly, the solution of (NH4)2HPO4 and glycine were added into that of the La(NO3)3 with vigorous stirring. The precursor solution was formed. Then, the precursor solution was heated until the white foam was obtained. The reaction took place in a few minutes and all the reactions happened in a wide-mouth beaker. A monoclinic lattice was verified in them by the investigation of X-ray diffraction (XRD). In the emission spectra of Eu3+, the 5D0→7F0 transition is often observed when Eu3+ is in low site symmetry because it is forbidden based on the group theory. The 5D0→7F1 transition is parity-allowed magnetic dipole transition, which is slightly affected by the symmetry of the Eu3+ site. The 5D0→7F2 transition is a parity forbidden electric dipole transition and strong emission only occurs in a non-inversion symmetry site. Under 254nm excitation, La3PO7:Eu3+ nanoparticles emitted mainly red fluorescence, assigned to the 5D0→7F2 transition of Eu3+ ions and revealed the Eu3+ ions occupied asymmetric sites in the oxyphosphate host. After annealing at different temperatures from 400℃ to 1200℃, we found that the higher the annealing temperature, the better the samples crystallized and the bigger the intensity ratio of I(5D0-7F2)/I(5D0-7F1). In comparison with LaPO4:Eu3+, an orange phosphor with stronger 5D0→7F1 emission, La3PO7:Eu3+ has prominent red luminescence under the same excitation and maybe become a promising red phosphor for PDPs and Hg-free fluorescent lamp in the future.关键词：La3PO7：Eu3+nanoparticles;combustion method;photoluminescence properties98|86|3更新时间：2020-08-11
- 摘要：Cr4+-doped YAG (Y3Al5O12) crystal is an ideal material used for passive-Q-switch, especially used in high power and high repetition rate lasers. Nd3+-doped YAG crystal is the best gain medium at present. Since 1995 Ikesue et al. firstly demonstrated the possibility of fabricating transparent Nd:YAG ceramics of sufficient quality for solid-state lasers, polycrystalline ceramic laser materials have attracted much attention because the optical quality has been improved greatly and highly efficient laser output could be obtained whose efficiencies are comparable or superior to those of single crystal. The purpose of the work is to combine the advantages of the gain medium Nd3+ and the saturable absorber Cr4+ using ceramic technology.The transparent Cr4+,Nd3+:YAG ceramics were fabricated by a solid-state reaction and vacuum sintering with CaO as a charge compensator, tetraethyl orthosilicate (TEOS) as a sintering aid and high-purity α-Al2O3, Y2O3, Nd2O3 and Cr2O3 powders as starting materials. The absorption spectra, fluorescence spectra and fluorescence of the 0.1%Cr,1.0%Nd:YAG transparent ceramics were measured at room temperature. For the Cr4+,Nd3+:YAG transparent ceramic sintered at 1800℃ for 30h, the absorption cross section, is 4.27×10-20cm2 at 808 nm, emission cross section and fluorescence lifetime are 1.52×10-20cm2 and 206 μs at 1 064 nm, respectively. The laser performance parameters of the gained Cr4+,Nd3+:YAG transparent ceramic were evaluated by Isat, βmin and Imin based on the spectroscopic parameters. The pump saturation intensity parameter Isat, the βmin parameter which is defined as the minimum inversion fraction of Nd3+ ions that must be exited to balance the ions exactly with the ground-state absorption at the extraction wavelength, and the minimum absorption pump intensity Imin to reach the threshold at the extraction wavelength are 28.0kW/cm2, 52.2% and 14.6 kW/cm2, respectively. High-quality Cr4+,Nd3+:YAG transparent ceramics, which combine the gain media and the saturable absorber together, may be a potential self-Q-switched laser material.关键词：Cr;Nd：YAG transparent ceramics;spectroscopic properties;laser performance parameters;self-Q-switched laser131|213|5更新时间：2020-08-11
- 摘要：It has been shown that high reflectivity mirrors can be formed by deeply etched semiconductor/air distributed Bragg reflectors (DBRs). The DBR structures are almost identical to multilayers of semiconductor and air. Current etching technologies can produce deep uniform etches in semiconductors. The finite dif-ference time domain (FDTD) method directly solves Maxwell’s equation in time. It is remarkably robust, providing accurate modeling for various electromagnetic wave interaction and field problem. Rapid advances in computer technology make the FDTD method more and more attractive every day. In this work we use the FDTD method in two dimensions to study a GaN-based semiconductor/air DBR structure. We take account of the TE mode and considering the geometry to be invariant in the lateral direction perpendicular to the light propagation. The spectral reflectivity is calculated by comparing the spectral content of the incident and reflected pulse. FDTD simulations show that vertical sidewall tilt is a crucial concern for obtaining a high-reflectivity DBR in a conventional design. The middle widths of semiconductor should increase to obtain the high reflec-tivity with the sidewall angle decreasing. To obtain high reflectivity at designed wavelength, the difference of optical path for one DBR pitch should keep constant. When the sidewall tilted, the difference of optical paths decrease. This phenomena can be explained using the knowledge of interference. To increase the optical paths difference, the air space and/or semiconductor width should be increased. The increase of air space will also increase the diffractive spreading loss, which arises because modal confinement is limited to the semiconductor region. In the air gaps, light is not confined and the refractive index of the air is much lower than that of the semiconductor, the optical field diverges quickly upon reaching the semiconductor-air interface. So, the semiconductor width should be increased to increase the optical width. Thus, high reflectivity can be reached with the proper design even with a large vertical sidewall tilt. Experimentally, it is difficult to etch vertical sidewalls of GaN-based materials, so the new design to overcome this difficulty is very meaningful.关键词：FDTD;DBR;reflectivity;tilt;interference93|128|0更新时间：2020-08-11
- 摘要：Taking the strong built-in electric field into account, the optical-rectification (OR) coefficient in a nitride semiconductor coupling quantum well (CQW) has been theoretically investigated by using the compact density matrix approach in the present paper. In general, in order to obtain strong even-order optical nonlinea-rities, one should constitute a quantum confined systems with asymmetrical potential profile, such as compositionally asymmetric quantum well (QW), and applied-field-based QW. It is well known that there exists very strong built-in electric field in GaN-based heterostructure due to the strong spontaneous macroscopic polarization and large piezoelectric coefficients. For the commonly used [0001]-oriented InGaN/GaN strained QW, the magnitude of the built-in electric field is estimated to be in the order of MV/cm. The built-in electric field with order of MV/cm can naturally break the inversion symmetry of the nitride quantum confined potential profile. Hence a very large even-order optical nonlinear susceptibility can be expected in such systems. Based on the built-in electric field model already constituted in recent reference, the electronic eigenstates in a nitride CQW are exactly solved. Numerical calculation on a typical GaN/InxGa1-xN CQW was performed. The calculated results reveal that the resonant OR coefficient achieves the magnitude of 10-6 m/V, and the dipole matrix elements of the systems also reach more than 2nm, which is apparently larger than the corresponding values in single wurtzite quantum wells. Moreover, we find that the OR coefficients of the CQW are not monotonic functions of the well width, barrier width and the doped concentration of the CQW systems, but have complicated dependent relations on them. The reason resulting in this characteristic is mainly attributed to the intense competition between the strong built-in electric field effect and the quantum size effect for the carrier in the wurtzite CQW systems. Our calculation also shows that a strong OR effect can be realized in the nitride CQW by choosing optimized structural parameters and relatively low doped fraction.关键词：nitride semiconductors;coupling quantum wells;built-in electric field;optical rectification effect90|135|0更新时间：2020-08-11
- 摘要：The forward current-voltage characteristic and forward capacitance-voltage characteristic measurings are the most important methods to study the forward electrical characteristic of GaN light-emitting diodes. We can use the forward alternating current (ac) small signal method to measure the capacitance-voltage charac-teristic of the GaN light-emitting diodes. Some values of GaN light-emitting diodes parameters can be deduced from capacitance-voltage characteristic. The negative capacitance phenomenon of GaN light-emitting diode can be observed by using this method. The negative capacitance phenomenon appears more noticeable when the bias voltage is lager and the frequencies of forward alternating current (ac) small signal are lower. In this paper, we propose that the phenomenon of measured negative capacitance is as the superficial phenomenon, and there no negative capacitance exists in fact. We propose that the p-n junction capacitance of GaN light-emitting diode is equivalent to a variable capacitance in a certain range of forward voltage. By analysis the responds of variable capacitance to the forward alternating current small signal, we find that the variable capacitance for specific parameter can make the current phase of junction capacitance behind the voltage phase of alternating current small signal, lead the variable capacitance behave as a negative capacitance on measu-ring. The behavior of a GaN light-emitting diode can be modeled by the equivalent electrical circuit which has a capacitance with a series resistance. There is an extreme point of apparent capacitance-forward voltage curve when use the equivalent circuit for measurement. We analyze the extreme point with the theoretical model of the variable capacitance for specific parameter. The result of theory analysis tallies with the experiment. That proved the accuracy of this theory model. The research on negative capacitance phenomenon will be valuable for study the electrical characteristics of GaN light-emitting diodes, will be valuable for the knowledge improvement of the characteristic and parameter relevant the p-n junction internal structure of GaN light-emitting diodes.关键词：GaN light-emitting diode;negative capacitance;forward alternating current (ac) small signal method;variable capacitance;extremum103|94|0更新时间：2020-08-11
- 摘要：Light-emitting diodes (LEDs) are a strong candidate for the next-generation general illumination applications. LEDs are making great strides in brightness performance and reliability; however, the barrier to widespread use in general illumination still remains the cost (dollars per lumen). For increasing the luminous flux of LED, the input power for chip of LED needs to be greater than before, and the thermal density inside LED will increase violently. However, the luminous efficiency and the life of chip will decrease at the high temperature condition, even the chip may be out of order or damaged. A good packaging technology is the way to solve the heat dissipation problem, but it is a challenge to develop this technology in the limited space of LED. The purpose of heat dissipating technology for LED is to decrease the working temperature of LED's chip. It is necessary to reduce the thermal resistance of LED package. The efficiency and reliability of solid-state lighting devices depends strongly on successful thermal management, because the junction temperature of the chip is the prime driver for effective operation. As the power density continues to increase, the integrity of the package electrical and thermal interconnects becomes extremely important.In this work, packaging experiments of high-power LEDs were studied using localized induction heating technique. The results show that, owing to the selectivity of induction heating with materials and geometry, only the electroless plated Cu-Sn alloy solder layer in chip area is heating and solder bonding between chip and copper-coated ceramic substrate is promised. Because of high thermal conductivity of Cu-Sn alloy, this novel packaging technique not only decrease the thermal resistance, making the p-n junction of LED kept at a low temperature even with a high current (four-fold of rated current), but also decrease thermal stress and avoid the damage of the chip, all of which will improve the performance and reliability of LED.关键词：light-emitting-diode(LED);packaging;induction heating;localized heating115|71|1更新时间：2020-08-11
- 摘要：The two-step growth method including growing the buffer layer on the substrate at a low-temperature and followed by growing the epitaxial layer at a high-temperature, was applied to grow high-quality InAs0.9Sb0.1 on (100) GaAs substrate by LP-MOCVD. The thickness of the buffer layer and the epitaxial layer are 30 nm and 0.7 μm, respectively.The composition and crystalline quality of InAsSb were examined by means of X-ray diffraction technique, the surface morphology of the epitaxial layers was observed by scanning electron microscopy (SEM) and the electrical property of samples was measured by Hall measurements using the Van Der Pauw method. The optical properties were examined by Raman scattering measurements. The effect of the growth temperatures of both the buffer layer and the epitaxial layer on the surface morphology of the epitaxial layer has been studied. The surface morphology was found to be essentially dependent on the growth temperatures of both the buffer layer and the epitaxial layer. Generally speaking, growing a buf-fer layer between the substrate and the epitaxial layer can decrease effectively the misfit dislocations generated by the lattice mismatch between them. The experiment shows that the epitaxial layer has poor crystalline quality if the growth temperature of the buffer layer is higher. A possible explanation is the buffer lattice grown at higher temperature would become too perfect to relax stress. As a result, the misfit dislocation was extend to the epitaxial layer and formed the poor surface morphology, but the buffer layer grown at the lower temperature can decrease effectively the misfit dislocations generated by the lattice mismatch between the substrate layer and the epitaxial layer. Finally, the optimum growth temperature of the buffer layer was range from 430℃ to 450℃. In the other side, the surface morphology would become poor for the epitaxial layer at higher growth temperature. The optimum growth temperature of the epitaxial layer should be selected between 480℃ to 500℃. The high quality InAs0.9Sb0.1 epitaxial layer with mirror-like surface, carrier concentrations of 1.9×1017 cm-3 and mobility of 6214 cm2/V·s has been obtained. The results of Raman scattering at room temperature showed that InAs0.9Sb0.1 have a two-mode behavior. The InAs-like(LO)peak at 233cm-1 and InSb-like(LO)peak at 187cm-1 could be observed for InAs0.9Sb0.1. At the same times, both InAs (TO) peak at 215cm-1 and disorder-activated longitudinal acoustic (DALA) phonons peak at 135cm-1 were also observed.关键词：MOCVD;InAsSb;two-step growth method;GaAs96|54|0更新时间：2020-08-11
- 摘要：The prepare processing and electrochromic characteristics of all solid-state plastic electrochromic devices are discussed. We chose WO3 thin film as cathode electrochromic material and NiOx thin film as counter electrode. All of these two thin films were coated on ITO plastic substrate respectively by low voltage reactive ion plating technology. Spectrum characters of as-deposited,bleached and colored state of these two thin films with different coating parameters were contrasted to optimize processing. It was tested that transmittance changes of WO3 film was about 35% with argon pressure of 2.2×10-2 Pa and oxygen pressure of 4×10-2 Pa, transmittance changes of NiOx film was about 18% with argon pressure of 2.5×10-2 Pa and oxygen pressure of 6×10-2 Pa. Then we synthesized MPEO-LiClO4 polymer as solid-state electrolyte, which was put in the middle of WO3 and NiOx film. After binding, assembling and sealed by plastic protective films, a new type of all solid-state plastic electrochromic device with plastic/ITO/WO3/MPEO-LiClO4/NiO/ITO/plastic structure has been successful fabricated. The spectrum characters of this electrochromic device in bleached and colored states were contrasted in two-electrode cell. The changes of transmittance were real-time measured by spectrophotometer. The results show that electrochromic characters were getting stable after ten times of cycles, and changes of transmittance was about 30%. The color change of device sample could be visual displayed, so we think this all solid-state plastic electrochromic device could be widely applied in display, electrochromic windows and other fields, through making use of such electrochromic properties. It was proved that electrochromic device could be prepared on the plastic substrate with all solid-state structure, and the prepare processing was feasible. But compared with electrochromic device prepared on glass substrate with liquid electrolyte, electrochromic properties and performance of this all solid-state plastic electrochromic device need to more improve and lucubrate.关键词：electrochromic;all solid-state;plastic116|94|0更新时间：2020-08-11
- 摘要：Recently, on the experiments, the characteristic of field electron emission of different novel semiconductor films and a variety of experimental methods to prepare semiconductor films have been paid more attentions. However, on the theories, there are rarely the related new reports. The main reason is that the traditional theories of field electron emission have not been adapted well to the novel nanomaterials which show different characteristics from the general semiconductor materials. So, it is necessary to set up a theoretical model to resolve the problem preliminarily. In the paper, by developing and improving conventional Fowler-Nordheim (F-N) field emission model considering electron scattering when electron transmits through the semiconductor film, the effect of thin-film thickness on field electron emission under the influence of an applied electric field has been studied theoretically. Barriers restricting electron transmission have an obviously change with the variation of the thickness of semiconductor film materials, so the current density of field electron emission also changed due to the variation of transmissive electron numbers. Results show that it is prominent for the effect of the film thickness on field electron emission. With the increase of the film thickness, there appears a worst film thickness value and an optimal film thickness value later for properties of field electron emission, which agreed well with some experimental reports. Correspond with this, the turn-on electric field appears a maximum and a minimum one after the other, however, the field electron emission current appears a minimum and a maximum one after the other. Furthermore, by analyses, distinct effects of the semiconductor film thickness on field electron emission may originate from the change of the area of effective tunneling barrier and the attenuation of electron scattering. Based on the model, not only some experimental results can be interpreted well, but also it can offer a theoretical guidance to the design of some vacuum microelectronic devices.关键词：field emission effect of thin-film thickness;area of effective tunneling barrier;attenuation of electron scattering102|103|0更新时间：2020-08-11
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The Application of Image Processing Technology in Low-work-function Printable Field Emission Display
摘要：Field emission display is a relative novel flat plate display. It is a promising technology as well as liquid crystal display, plasma display panel, OELD. The large-screen printing FED developed with indepen-dent intellectual property rights used particular low-cost, large-scale, low work function material and cathode slurry. Different from FED of other types, large-scale printing FED is with low cost, simple technic,and using the materials with low work function, thus it can reduce the emitting voltage, simplify the driving circuit. At present, we have developed 25 inches large-screen printing color field emission display, topping in China. In the year before last, we successfully developed a kind of driving system that realized displaying video on FED panel. The system used special image processing technology. So far, the driving system has been applied to the 640×480 FED panel and reached good result. The principle of low work function printable field emission display system was presented including the transform and processing of digital video image, the transmission of video data, the interface circuit, the gray-shade of column driving and the row driving technologies, as well as, FPGA control technology. In order to improve display result of the printable field emission display, the luminance non-uniformity correction me-thod, gamma correction method and automatic power control method are proposed by theoretical analyzing and practical certificating. Image processing method is used into the driving circuit and image luminance uniformity and gray-scale reproduction quality are improved, the sample power consume is also reduced. At present, the technology has been used in the 25 inch color low work function printable FED sample fabricated with the capacity for image processing in our lab. It can display color video images and the obtained brightness is about 400 cd/m2,contrast ratio 1000:1 and 256 circuit gray scales.关键词：field emission display;nonlinear luminance;Gamma emendation;auto power control;FPGA99|221|5更新时间：2020-08-11 - 摘要：Since the photo electrochemical cell was used in the conversion of the solar energy to the electrical power or to hydrogen, more and more attention has been paid in this field. The photocathode plays an important roll in the electrochemical chain of PEC. In this paper, the p-n junction was used to improve efficiency of the photocathode because the inner electric field of the p-n junction can make the photo-generated carriers separate more easily. The NiO electrode and the NiO-TiO2 hybrid electrode were fabricated on the SnO2:F (FTO) transparent conducting glass via sol-gel method. The solution was prepared by using the nickel acetate tetra hydrate and the tetra-n-butyl tianate as precursors. The films were obtained by spin-coating method and then annealed at 450℃ in air for three hours. The crystal structures of the films were characterized by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was also used to investigate the microstructures of the films. The XRD results showed that all the strongest peaks were indexed to the anatase TiO2 and the bunsenite NiO, respectively. From SEM, the surface of the film was quite compact, the grains were nanometer-sized and the thicknesses of NiO and TiO2 layer were 200nm and 130nm, respectively. Moreover, the photoelectrochemical properties of the NiO and the NiO-TiO2 hybrid electrode were also investigated under 500W Xe arc lamp illumination. It was found that the cathode photocurrent of the NiO-TiO2 hybrid electrode was larger than that of the NiO electrode and that the flat-band potential of the hybrid electrode was also more positive than that of NiO electrode. Therefore, the results indicated that the photo-generated carriers could be separated and transferred more easily for the build-in electric field of the p-n junction. Besides, an energy band diagram of the p-n junction was proposed to explain the results in this paper.关键词：p-n junction;photocathode;PEC;photocurrent106|83|0更新时间：2020-08-11
- 摘要：It is common that the p-type wide-gap semiconductors are difficult to obtain, however, it is fortunate to observe that the delafossite structured ABO2 (A=Cu or Ag; B=Al, Cr, or La) compounds are p-type wide-gap semiconductors with high optical transparency, and the gap is higher than 3.1 eV for these mate-rials. The ABO2 compounds also show rather large power factor compared to other oxide materials. Therefore, it is expected to apply these materials in transparent semiconducting devices as well as in thermoelectric applications.The delafossite structured single phase CuBO2(B=Al,Cr,La)ceramics were synthesized by sol-gel and high temperature solid state reaction, respectively. Moreover, CuCrO2 films were prepared by pulsed laser deposition (PLD) using the synthesized single phase CuCrO2 ceramics as targets. The crystallization and microstructure of the samples were investigated by X-ray diffractometer (XRD) and field-emission scanning electron microscope (FE-SEM). The electron dispersion spectrum (EDS) was also used to determine the chemical composition. The temperature dependence of conductivity was measured by the standard two-probe method. Optical transmission spectra of the films were measured by a dual beam spectrophotometer. The study results showed that sol-gel was an effective approach to synthesize single phase CuAlO2 and CuCrO2 ceramics, with shorter sintering period and lower annealing temperature. The temperature dependence of conductivity for CuAlO2 and CuCrO2 ceramics showed that these two materials behaved as semiconductors around room temperature. Additionally, the room temperature conductivity of CuBO2(B=Al,Cr,La) decreased obviously with the increase of the radius of ions on B site. CuCrO2 thin films with high c-axis orientation were successfully prepared by PLD, and the optical transmittance of the CuCrO2 film with the thickness ~200 nm was about 80% in the visible region.关键词：sol-gel;delafossite;transparent conductive oxide;pulse laser deposition;thin film127|82|1更新时间：2020-08-11
- 摘要：The photoelectrochemical cells based on semiconductor-liquid junctions have attracted much attention because of their potential application, such as solar energy converters. In the cell system, it is important to produce the high efficiency photoelectrodes that are stable in aqueous solution and that absorb a significant portion of the solar spectrum effectively. Much effort has been done to find new materials and new electrode structures in order to produce efficient photoelectrodes. Along with its abundance and low cost, α-Fe2O3 has narrow band gap, strong absorptivity in the visible range and good stability in aqueous solution. So it has been of considerable interest in its use as a photocatalyst and a photoelectode. However, the photocurrent quantum efficiency of α-Fe2O3 is too low to limit its further application in converting solar energy. In general, recombination of electrons and holes cased by low mobilities of holes and trapping of electrons by oxygen-deficient iron sites are considered to be responsible for the low conductivities and poor photocurrent efficiencies of iron oxide photoelectrode.To suppress the recombination of electrons and holes thus to improve the photocurrent quantum efficiency, the semiconductor films of SrTiO3, α-Fe2O3 and their heterojunction SrTiO3/α-Fe2O3 were prepared on FTO (SnO2:F on glass) substrates by the spin-coating method. The XRD pattern, SEM and transmission spectra of SrTiO3/α-Fe2O3 film photoanode were characterized in our experiments. The anodic photocurrent-potential characteristics and the action spectra were studied in a three-electrode cell employing the film electrode as the working electrode with the electrolyte Na2SO4(0.2 mol/L, pH≈7.5). It was found that under 0.3 V bias voltage, the photocurrent and the incident photon to current conversion efficiency (IPCE) of the SrTiO3/α-Fe2O3 film was higher than that of SrTiO3 or α-Fe2O3 films alone, which is consonant with our theoretical calculation conclusions by using the standard CASTEP package.关键词：heterojunction;photoanode;photoelectrochemical cell;photocurrent;IPCE100|49|2更新时间：2020-08-11
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