Efficiency of a blue organic light-emitting diode enhanced by inserting charge control layers into the emission region

We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode （OLED） by using the charge control layers （CCLs） based on Alq3 . The CCLs that are inserted into the emitting layers （EMLs） could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2 , which is about 2.19 times higher than that of the control device （CD） without the CCL, and the maximal luminance is 19.660 cd/m2 at 12V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.

Novel measurement scheme of peak separation of side-hole fiber grating

There are two peaks of different polarizations in the reflection spectrum of the side-hole fiber grating and their separation interval has a linear variation along with the pressure changing while it is insensitive to the temperature.We have proposed a novel measurement scheme based on polarization detection.The detection of peak separation is achieved by measuring the two peaks’ center wavelengths separately with all polarization maintaining fiber system.The side-hole fiber grating pressure sensing within the range of 0～3.5 MPa is realized successfully with the new scheme.

Plasma assisted molecular beam epitaxial growth of GaN with low growth rates and their properties

A systematic investigation on PA-MBE grown GaN with low growth rates(less than 0.2μm/h)has been conducted in a wide growth temperature range,in order to guide future growth of sophisticated fine structures for quantum device applications.Similar to usual growths with higher growth rates,three growth regions have been revealed,namely,Ga droplets,slightly Ga-rich and N-rich 3D growth regions.The slightly Ga-rich region is preferred,in which GaN epilayers demonstrate optimal crystalline quality,which has been demonstrated by streaky RHEED patterns,atomic smooth surface morphology,and very low defect related yellow and blue luminescence bands.The growth temperature is a critical parameter to obtain high quality materials and the optimal growth temperature window(~700-760℃)has been identified.The growth rate shows a strong dependence on growth temperatures in the optimal temperature window,and attention must be paid when growing fine structures at a low growth rate.Mg and Si doped GaN were also studied,and both p-and n-type materials were obtained.

Properties of Parity Non-conserved and Parity Conserved States in Matrix Product Systems

In terms of reflection transformation of a matrix product state (MPS),the parity of the MPS is defined.Based on the reflective parity non-conserved MPS pair we construct the even-parity state |Ψ_e> and the odd-parity state|Ψ_o>.It is interesting to find that the parity non-conserved reflective MPS pair have no long-range correlations;insteadthe even-parity state |Ψ_e> and the odd-parity state |Ψ_o> constructed from them have the same long-range correlationsfor the parity non-conserved block operators.Moreover,the entanglement between a block of n contiguous spins and therest of the spin chain for the states |Ψ_e> and |Ψ_o> is larger than that for the reflective MPS pair except for n = 1,and thedifference of them approaches 1 monotonically and asymptotically from 0 as n increases from 1.These characteristicsindicate that MPS parity as a conserved physical quantity represents a kind of coherent collective quantum mode,andthat the parity conserved MPSs contain more correlation,coherence,and entanglement than the parity non-conservedones.

Markov Quantum Feedback Control Based on Homodyne Measurement of a Two-Qubit System

We consider the system consisting of two qubits collectively damped,with the output being unit-efficiencymeasured and subsequently fed back to control the system state.Our primary goal in this paper is (ⅰ) to solve thefeedback-modified master equation,(ⅱ) to demonstrate the ability of feedback control based on the solutions,and (ⅲ) topick out different steady states by choosing different driving strengths and feedback strengths to counteract the effects ofboth damping and the measurement back-action on the system.We further investigate some properties of the equilibriumsteady state,its distribution probability and entanglement vs.the driving and feedback amplitudes.We find that in ourfeedback model feedback plays a negative role in producing entanglement.

Attenuation characteristics of a light attenuator combined by polarizers with different extinction ratios

This paper deals with a systematical analysis and an algorithm of attenuation characteristics of a light attenuator combined by n pieces of polarizers （n-LACP） whose extinction ratios are different from each other. The attenuation ratio expression of a two-LACP is deduced. We find that the monotonic attenuation interval depends on the first polarizer and that the attenuation range depends on the second one. For the three-LACP, a method for obtaining a monotonic attenuation interval is proposed. Moreover, the attenuation ratio expression is demonstrated. Analysis and experiment show that when the initial status of the three-LACP is at the maximum output, if the second or third polarizer rotates alone, the minimum attenuation ratios can reach K2^-1 and K3^-1, respectively, and if the first polarizer rotates, a minimum attenuation ratio of K2^-1K3^-1 can be obtained （K1, K2 and K3 represent the extinction ratios of the three polarizers in turn）. Furthermore, the attenuation ratio expression of n-LACP and the relevant attenuation characteristics are proposed. The minimum attenuation ratio of an n-LACP is （K2K3 ... Kn）-1.

Structural characterization of Al_(0.55)Ga_(0.45)N epitaxial layer determined by high resolution x-ray diffraction and transmission electron microscopy

Structural characteristics of Alo.55 Gao.45N epilayer were investigated by high resolution x-ray diffraction（HRXRD）and transmission electron microscopy（TEM）;the epilayer was grown on GaN/sapphire substrates using a high-temperature A1 N interlayer by metal organic chemical vapor deposition technique.The mosaic characteristics including tilt,twist,heterogeneous strain,and correlation lengths were extracted by symmetric and asymmetric XRD rocking curves as well as reciprocal space map（RSM）.According to Williamson-Hall plots,the vertical coherence length of AlGaN epilayer was calculated,which is consistent with the thickness of AlGaN layer measured by cross section TEM.Besides,the lateral coherence length was determined from RSM as well.Deducing from the tilt and twist results,the screw-type and edge-type dislocation densities are 1.0×10~8 cm^（-2） and 1.8×10^（10） cm^（-2）,which agree with the results observed from TEM.

Theoretical investigation on the electronic structure,elastic properties, and intrinsic hardness of Si2N20

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli （bulk modulus, Young’s mod-ulus, and shear modulus） are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.

Atmosphere Transmission Performance for 0.4 μm～0.8 μm Ray Radiation in Middle Latitude of China

This paper researched on the atmospheric transmission performance of 0.4 μm～0.8 μm ray radiation based on the characteristic of the middle latitude atmosphere in China.By analysis of the characteristic of the actual atmosphere,the absorption of molecular and the scattering of the steam and ozone,as well as the aerosol scattering(big granule scattering) are play a leading role to the 0.4 μm～0.8 μm ray radiation.Then a better atmospheric transmission formula in horizontal path has been deducted.The result of computer simulation indicates that this equation can best calculate the transmission performance of 0.4 μm～0.8 μm visible radiation in the middle latitude area of China.This computing result was applied to the nuclear explosion parameter detection system based on 0.4 μm～0.8 μm visible radiation.Through nuclear explosion simulator to produce ray radiation,the tested result indicates that this method has the better measuring precision than the traditional method with the software of LOWTRAN.The calculation result of this formula not only can apply directly to each kind of optoelectronics detecting system,but also to the optical wireless communication system based on the 0.4 μm～0.8 μm ray radiation.

Syntheses and Crystal Structures of 9-Ethyl-1,3,6,8-tetra-aryl-9H-carbazole Compounds

The title compounds 9-ethyl-1,3,6,8-tetra-p-tolyl-9H-carbazole （1） and 9-ethyl-1,3,6,8-tetrakis-（4-fluoro-phenyl）-9H-carbazole （2） were synthesized and characterized by single-crystal X-ray diffraction. Thereinto, the crystal structures of compounds 1 and 2 were composed by asymmetry units. The ratio of compounds 1 and 2 to the solvent molecule cyclohexane （CYH） is 4/3. X-ray analysis reveals that the 1,3,6,8-phenyl groups are distorted at large angles relative to the planar carbazole ring. Furthermore, the luminescent and thermal properties of 1 and 2 have also been investigated. It can be seen that thermal stability of compound 1 with p-tolyl is better than that of 2 with 4-fluoro-phenyl. Fluorescence spectra analysis showed that compounds 1 and 2 have strong UV emission.

Equal compressibility structural phase transition of molybdenum at high pressure

We have studied the high-pressure compression behavior of molybdenum up to 60 GPa by synchrotron radial x-ray diffraction(RXRD)in a diamond anvil cell(DAC).It is found that all diffraction peaks of molybdenum undergo a split at around 27 GPa,and we believe that a phase transition from a body-centered cubic structure to a rhombohedral structure at room pressure has occurred.The slope of pressure–volume curve shows continuity before and after this phase transition,when fitting the pressure–volume curves of the body-centered cubic structure at low pressure and the rhombohedral structure at high pressure.A bulk modulus of 261.3(2.7)GPa and a first-order derivative of the bulk modulus of 4.15(0.14)are obtained by using the nonhydrostatic compression data at the angleψ=54.7°between the diffracting plane normal and stress axis.

Electron excitation processes in low energy collisions of hydrogen-helium atoms

The electron excitation processes of H(1s)+He(1s^(2))→H(2s/2p)+He(1s^(2))are studied in impact energy range of 20-2000 e V/u by using the quantum-mechanical molecular orbital close-coupling(QMOCC)method.Total and state-selective cross sections have been obtained and compared with the available theoretical and experimental results.The results agree well with available measurements in the overlapping energy regions overall.The comparison of our results with other theoretical calculations further demonstrates the importance of considering a sufficient number of channels.The datasets presented in this paper,including the excitation cross sections,are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00083.

Mg acceptor activation mechanism and hole transport characteristics in highly Mg-doped AlGaN alloys

The Mg acceptor activation mechanism and hole transport characteristics in AlGaN alloy with Mg doping concentration(~ 1020 cm-3) grown by metal–organic chemical vapor deposition(MOCVD) are systematically studied through optical and electrical properties. Emission lines of shallow oxygen donors and(VⅢ complex)1- as well as VN3+ and neutral Mg acceptors are observed, which indicate that self-compensation is occurred in Mg-doped AlGaN at highly doping levels. The fitting of the temperature-dependent Hall effect data shows that the acceptor activation energy values in Mgdoped AlxGa1-xN(x = 0.23, 0.35) are 172 meV and 242 meV, and the hole concentrations at room temperature are 1.2×1018 cm-3 and 3.3× 1017 cm-3, respectively. Therefore, it is believed that there exists the combined effect of the Coulomb potentials of the dopants and screening of the Coulomb potentials by a high hole concentration. Moreover, due to the high ionized acceptors’ concentration and compensation ratio, the impurity conduction becomes more prominent and the valence band mobility drops sharply at low temperature.

Low driving voltage in an organic light-emitting diode using MoO_3/NPB multiple quantum well structure in a hole transport layer

The driving voltage of an organic light-emitting diode（OLED） is lowered by employing molybdenum trioxide（MoO3）/N,N＇-bis（naphthalene-1-yl）-N,N＇-bis（phe-nyl）-benzidine（NPB） multiple quantum well（MQW） structure in the hole transport layer.For the device with double quantum well（DQW） structure of ITO/[MoO3（2.5 nm）/NPB（20 nm）]2/Alq3（50 nm）/LiF（0.8 nm）/Al（120 nm）],the turn-on voltage is reduced to 2.8 V,which is lowered by 0.4 V compared with that of the control device（without MQW structures）,and the driving voltage is 5.6 V,which is reduced by 1 V compared with that of the control device at the 1000 cd/m2.In this work,the enhancement of the injection and transport ability for holes could reduce the driving voltage for the device with MQW structure,which is attributed not only to the reduced energy barrier between ITO and NPB,but also to the forming charge transfer complex between MoO3 and NPB induced by the interfacial doping effect of MoO3.

High Speed Signal Wavelength Conversion Using Stimulated Raman Effect in Ultrasmall Silicon-on-Insulator Optical Waveguides

我们在硅波导上基于刺激拉曼效果建议高速度信号波长变换。假散乱咬了的 non-return-to-zero (NRZ ) 的模拟结果定序(2 (7 )-1 代码) 以在极端小 silicon-on-insulator (SOI ) 的变换的 500-Gb/s 率，光波导被共同繁殖介绍泵光地。最吸引人的问题是转换变换信号能在象主要信号的一样的波长被获得。另外，变换表演，包括扑灭比率(嗯) 并且变换信号的平均山峰力量，强烈取决于发射的泵紧张。

GaN hexagonal pyramids formed by a photo-assisted chemical etching method

A series of experiments were conducted to systematically study the effects of etching conditions on GaN by a con-venient photo-assisted chemical （PAC） etching method. The solution concentration has an evident influence on the surface morphology of GaN and the optimal solution concentrations for GaN hexagonal pyramids have been identified. GaN with hexagonal pyramids have higher crystal quality and tensile strain relaxation compared with as-grown GaN. A detailed anal- ysis about evolution of the size, density and optical property of GaN hexagonal pyramids is described as a function of light intensity. The intensity of photoluminescence spectra of GaN etched with hexagonal pyramids significantly increases compared to that of as-grown GaN due to multiple scattering events, high quality GaN with pyramids and the Bragg effect.

Scanless multitarget-matching multiphoton excitation fluorescence microscopy

Using the combination of a refective blazed grating and a reflective phase-only difractive spatiallight modulator(SLM),scanless multitarget-matching multiphoton excitation fuorescence mi.croscopy(SMTM-MP M)was achieved.The SLM shaped an incoming mode-locked,near-infraredTi:sapphire laser beam into an excitation pattern with addressable shapes and sizes that matchedthe samples of interest in the field of view.Temporal and spatial focusing were simultaneouslyrealized by combining an objective lens and a blazed grating.The fluorescence signal fromilluminated areas was recorded by a two-dimensional sCMOS camera.Compared with a conventional temporal focusing multiphoton microscope,our microscope achieved effective use of thelaser power and decreased photodamage with higher axial resolution.

Moving Objects Detection Using Intersecting Cortical Model in Enhanced Fish-eye Image

A new method of the moving objects detection using the enhanced fish-eye lens and the intersecting cortical model(ICM) algorithm is proposed. The improved fish-eye lens is designed through controlling the entrance pupils of the lens. This lens has an ultra field of view about 183 degrees,and can image an ellipse picture on the 4∶3 rectangular CCD surface,which increases the CCD utilization and the image resolution. The ICM is a model based on pulse coupled neural network(PCNN) which is especially designed for image processing. It is derived from several visual cortex models and is basically the intersection of these models. The theoretical foundation of the ICM is given. An improved ICM algorithm in which some parameters are modified is used to detect moving objects specially. The experiment indicated that moving objects can be detected reliably and efficiently using ICM algorithm from the elliptical fish-eye image. It can be used in the field of traffic monitoring and other security domains.

Study on New Concatenated Code in WDM Optical Transmission Systems

A new concatenated code of RS(255,239)+BCH(2 040,1 930) code to be suitable for WDM optical transmission systems is proposed. The simulation results show that this new concatenated code, compared with the RS(255,239)+CSOC(k0/n0=6/7, J=8) code in ITU-T G.75.1, has a lower redundancy and better error-correction performance, furthermore, its net coding gain(NCG) is respectively 0.46 dB, 0.43 dB more than that of RS(255,239)+CSOC(k0/n0 =6/7, J=8) code and BCH(3 860,3 824)+BCH(2 040,1 930) code in ITU-T G.75.1 at the third iteration for the bit error rate(BER) of 10-12. Therefore, the new super forward error correction(Super-FEC) concatenated code can be better used in ultra long-haul, ultra large-capacity and ultra high-speed WDM optical communication systems.