注入式半导体发光二极管的新进展

可见光发光二极管(LED)是目前用量很大的一类半导体器件.由于发光效率不高,一直只能用作弱光光源(如指示灯)和各种信息显示器件(如各种数码管和收录机上的电平指示器),而不能用作强光光源.1983年7月,日本斯坦利公司的寺岛透等人报道了一种超高亮度的GaAlAs红光发光二极管[1],这种器件刷新了1972年以来一宜保持的12.6%外量子效率的实验室纪录,达到16%的发光效率,在20毫安电流下,器件的发光强度达2烛光.该器件已被用作十字路口的交通信号灯,成功地迈入了强光光源的行列. 器件的发光波长为6600埃,光谱半宽度为250埃;响应速度30—40毫微秒,比…     

两种蓝色有机电致发光材料

重点研究以两种蓝色OEL材料蒽类衍生物JBEM和联苯乙烯衍生物DPVBi分别作基质，以perylene作掺杂剂的器件的电致发光性能，特别研究了它稳定性，在这度和效率方面，两种器件并没有很大差别，然而在稳定性方面却有很大差别，蒽类衍生物JBEM的器件在100cd/m^2初始亮度下，半亮度寿命可达1035h，而DPVBi的器件在同样条件下，半亮度寿命为255h。通过分析两种器件的能级图，认为稳定性的差别可能源于两种蓝光材料本身的热稳定性不同，JBEM优于DPVBi，是一种很有前途的蓝色发光材料。     

具有金属反射腔的半导体平面发先器件设计原理

半导体平面发光二极管与发光二极管单管相比,具有较大的发光面、发光均匀、视角大等优点,在仪器仪共、大型厂矿的中央控制室以及军事指挥所的模拟屏等方面有广泛应用. 在某些应用中(例如将它装备在野外工作的代表上,将它作为飞机骂驶舱的告警显示、模拟显示,以及大型矩阵显示屏幕的发光单元),田于环境照变较高,要求发光器件具有更高的亮度.为了提高发光亮度,在管芯发光效率确定的条件下,我们应用物理学的一些基本原理,对发光器件的结构、材料作了最佳的选择和设计,达到了提高发光器件亮度的目的.图1是金属反射腔半导体平面发光器件的结构. …     

数字电视的光色计量及其装置

结合市面上常见数字电视器件CRT,LCD,PDP等的显示原理及特性，具体讲解光色计量指标测量方法及原理，系统量值传递是通过国家色度和亮度基准标准灯来完成的。利用虚拟仪器技术建立的数据采集及分析系统，可对待测仪器的参数进行实时数据检测和数据分析。整个测试系统亮度和色坐标不确定度小于2%和0.005. 通过对市场主流电视产品的集中检测，将其相对光谱功率分布、亮度、色坐标、亮度不均匀性及对比度等综合参数进行对比，给出了测试结果及各种电视性能分析，为数字彩色电视计量工作提供了参考。     

高功率980nm垂直腔面发射激光器的亮度特性

在循环水冷却(工作环境温度控制在15℃)和连续注入电流条件下,从垂直腔面发射激光器(VCSEL)亮度基本定义出发,实验测量了不同注入电流时口径为400μm的高功率980nm InGaAs/GaAs应变量子阱垂直腔面发射激光器(VCSEL)的亮度特性。结果表明:在注入电流4 A时,随着注入电流的增加,亮度也跟着增加;当注入电流4A时,尽管输出功率在增加,但是器件的光束质量变差,M2因子升高,表明此时影响器件亮度的主导因素是M2因子,所以亮度减小;在注入电流为4A,输出功率为1.2W时,亮度达到最大值2.43kW/cm2.sr,此时的光束质量最好,M2因子为207。最后,分析了影响高功率VCSEL器件亮度特性的主要因素,提出了提高器件亮度特性的解决方法。     

有机微腔绿色发光二极管

光学微腔是指尺寸在光波长量级的光学微型谐振腔。微腔结构可以使腔内物质和光场的相互作用与体材料相比发生很大变化,出现了自发辐射谱线窄化和增强等腔效应。利用这些腔效应,可以改善有机发光器件的性能。采用微腔结构,优化设计并研制了有机微腔绿色发光二极管,器件结构为Glass/DBR/ITO/NPB/Alq∶Rubrene/Alq/MgAg,获得了最大亮度40100 cd/m2、最大发光效率为6.44 cd/A、半峰全宽为28 nm的纯绿色有机微腔电致发光器件。而与之比较的无腔器件最大亮度为22580 cd/m2、最大发光效率为2.98 cd/A、半峰全宽为120 nm。相同电流密度下微腔电致发光谱的峰值发射强度是无腔器件的4.2倍。结果表明将微腔结构引入有机电致发光器件中,不但改善了发光的色纯度,而且使器件的发光效率和亮度都得到明显增强。     

Diamine的光、电性质及其在有机薄膜电致发光器件中的应用

合成了芳香族二胺类衍生物(diamine),测定了它的光、电性质.制备了diamine作为空穴传输层的二层结构有机薄膜电致发光器件,使器件的发光亮度相对单层器件有了很大的提高.并用不同区域掺杂的方法,探讨了电致发光机理.分析、讨论了激子的形成和复合区域,较好地解释了单、双层器件的不同的电流电压关系和不同的亮度电压关系.从激子的扩散方程出发,对双层掺杂器件的发光强度比数据进行了拟合,确证了激子的扩散模式.     

发光效率及稳定性改善的有机薄膜电致发光器件

不久前,我们报导了以TPD为空穴传输层,Alq为电子传输兼发光层的双层薄膜电致发光器件,在定电流密度6mA/cm2连续驱动下,初始亮度106cd/m2下降至一半亮度的时间为120小时,而继续操作500小时,亮度仍有38cd/m2[1]。在这篇文章中,我们将报道一个在上述器件的空穴传输层TPD中掺杂而构成的新器件。这个新器件发光亮度和效率比原器件增加了50%,而稳定性增加了近10倍,初始亮度165cd/m2的半亮度寿命达1200小时。     

一种白光有机电致发光器件的制备

通过对器件结构的优化设计，提高了白光电致发光器件中蓝光成分的发光效率，从而得到了一种较为理想的有机白光电致发光器件。驱动电压为5V时，电流密度J=0．5mA／cm^2，器件的效率达到最大，流明效率为1．92 lm／W，此时器件的发光亮度接近20cd／m^2。色坐标为(x=O．317，y=0．328)。非常接近白光等能点．是色度很好的白光。并且在很大范围内，色度随器件的驱动电压或电流变化不大，当驱动电压变化至15V时。f=232mA／cm^2，色坐标变化至(x=0．338，y=O．353)。在电压为22V时，器件的亮度达到最大，为17 000cd／m^2。此外器件结构相对简单。器件制备的可重复性得到很大程度的改善。     

水汽处理对量子点发光二极管的性能影响研究

在量子点电致发光二极管(quantum-dot light-emitting diodes, QLEDs)的研究中,外界空气尤其是水氧一直是影响器件性能的主要因素。而有研究表明水是导致QLED器件固定电流下亮度提升的原因之一,因此通过水汽处理的方式对这一效果进行提升有利于进一步优化器件性能。主要基于水对量子点表面缺陷态的钝化作用来研究水汽处理量子点发光层对电致发光器件整体性能的影响,并探索最佳处理时间。首先利用全溶液法制备了一系列QLED器件,并在制备过程中对量子点膜层进行水汽处理,通过保持湿度不变改变处理时长的方式改变水汽处理程度。然后对各个器件进行电致发光光谱的表征,结果表明经过水汽处理的QLED器件的电致发光光谱相对未处理器件有一定程度的蓝移,并且随着处理时间的延长蓝移程度增大,分析发现这是水分子氧化量子点引起表面钝化从而减少带边缺陷态发光的结果。此外,通过测量各个器件的电流密度-电压-亮度(J-V-L)曲线对比不同水汽处理时长下器件的电流密度和发光强度大小,并通过计算得到各器件的电流效率曲线。结果表明随着处理时间的延长, QLED器件的亮度和电流效率都取得较大幅度的提升,处理时长为3 min时亮度提升10%,电流效率提升50%。最后,利用寿命测试设备对器件进行老化,得到不同处理时长器件在相同固定电流密度下亮度随时间变化的曲线。结果表明各个器件亮度均表现出先提升后下降的过程,亮度初始提升幅度约为50%～70%,并且提升到最大值所用时长随处理时间的增大而减小,说明水汽处理对器件亮度提升更有效。通过寿命公式计算器件的寿命并进行对比,发现经水汽处理器件寿命相对未处理器件最高提升了70%。总之,水汽处理对QLED器件的性能在一定程度上起优化作用,这对于QLED器件效率和寿命的提升以及封装工艺的简化是十分有益的。     

ZnO:Zn低能电子发光的亮度饱和

本文讨论了ZnO:Zn低能电子发光亮度饱和的物理原因。指出,在Vg=Va(通常数字显示的情况)的条件下,亮度饱和的主要原因是ZnO:Zn次级电子发射和阴极发射疲劳;若取Vg=Va,则饱和亮度成倍提高,这时热猝灭将是亮度饱和的主要因素。同时指出,对于一定的输入功率,存在着一个与最佳效率相对应的最佳阳极电流密度;低阳极电流密度,高阳极电压往往是低效率的。作者根据本文的研究结果,制成了饱和亮度高达37,000cd/m2的发光管和饱和亮度为22,000cd/m2、能在5,000至10,000cd/m2稳定工作的高亮度数字显示管。后者配上适当的滤光片、在阳光直接照射或照度高达100,000lux的条件下仍能清晰地阅读。     

光折变聚合物中的小振幅空间光孤子

给出了稳态条件下光折变聚合物中的小振幅空间孤子的演化方程,得到了方程的暗、亮孤子解析解,并且给出了小振幅聚合孤子的宽度表达式结果表明,光折变聚合物中存在着双曲正切形式的小振幅暗空间孤子和双曲正割形式的小振幅亮空间孤子,小振幅聚合孤子的宽度与外加电场成反比关系.     

光折变聚合物中的小振幅空间光孤子(英文)

给出了稳态条件下光折变聚合物中的小振幅空间孤子的演化方程,得到了方程的暗、亮孤子解析解,并且给出了小振幅聚合孤子的宽度表达式。结果表明,光折变聚合物中存在着双曲正切形式的小振幅暗空间孤子和双曲正割形式的小振幅亮空间孤子,小振幅聚合孤子的宽度与外加电场成反比关系。     

Temporal behavior of spatial solitons in centrosymmetric photorefractive crystals

We investigate theoretically the time behavior of spatial solitons in biased centrosymmetric photorefractive crystals. A one-dimensional time-dependent wave propagation equation in biased centrosymmetric photorefractive crystals is presented. It is shown that the bright solitons exist in both quasi-steady-state and steady-state regimes for high saturation values. When the intensity ratio is smaller than unity, the bright soliton width decreases monotonically to a minimum value toward steady state. Moreover, the time-dependent nonlinear wave equation exhibits only steady-state screening dark spatial solitons.     

基于MEMS光栅平动式光调制器信号处理分析

依据傅里叶光学理论,采用在频谱面上放置两种空间滤波器的方法进行信号处理,分析了光栅平动式光调制器在成像面上的强度分布情况,实现了对光能量的调制.分析表明：当滤出±1级谱时,像面上可以得到完全均匀的暗场；但是由于边框和悬臂梁的影响,得不到完全均匀的亮场；当滤出零频谱时,由于边框和悬臂梁的影响,得不到完全均匀的暗场和亮场.设计时,为了要在像面上得到更高的亮度均匀性,需要满足可动光栅栅条宽度为光栅周期的一半,同时应尽量减少悬臂梁和边框的宽度.     

An Integrated Circuit for Two-Dimensional Edge-Detection with Local Adaptation Based on Retinal Networks

We designed an integrated circuit for edge detection of a two-dimensional image based on the vertebrate outer retina, which has wide dynamic range in image processing. The unit circuit is simple, and operates as a current-mode analog metal-oxide-semiconductor (MOS) circuit. In order to extract edges from an image composed of bright and dark domains, the circuit realizes a function called local adaptation in which the sensitivity adapts to local brightness of the image. Simulation results, using the simulation program with integrated circuit emphasis (SPICE), of two-dimensional Gaussian-distributed images in which the intensity ranged over four orders of magnitude, showed the local adaptation. As a result, the intensity of output images was in the range of one order of magnitude. Furthermore, as the simulation result of real images, it was shown that edges in the dark domain, which was five times darker than the bright domain, were successfully detected as the bright domain in which input photocurrents ranged over two orders of magnitude.     

Complex adaptation-based LDR image rendering for 3D image reconstruction

A low-dynamic tone-compression technique is developed for realistic image rendering that can make three-dimensional (3D) images similar to realistic scenes by overcoming brightness dimming in the 3D display mode. The 3D surround provides varying conditions for image quality, illuminant adaptation, contrast, gamma, color, sharpness, and so on. In general, gain/offset adjustment, gamma compensation, and histogram equalization have performed well in contrast compression; however, as a result of signal saturation and clipping effects, image details are removed and information is lost on bright and dark areas. Thus, an enhanced image mapping technique is proposed based on space-varying image compression. The performance of contrast compression is enhanced with complex adaptation in a 3D viewing surround combining global and local adaptation. Evaluating local image rendering in view of tone and color expression, noise reduction, and edge compensation confirms that the proposed 3D image-mapping model can compensate for the loss of image quality in the 3D mode.     

Bright and dark solitons for a variable-coefficient $$$$ dimensional Heisenberg ferromagnetic spin chain equation

Under investigation in this paper is a variable-coefficient \((2+1)\) dimensional Heisenberg ferromagnetic spin chain equation. Bilinear forms for the bright and dark soliton solutions are respectively obtained. Bright and dark solitons are obtained via the Hirota bilinear method. Features of the bright and dark solitons are discussed. Interaction properties of the bright and dark solitons are discussed via the asymptotic analysis, and stability of the bright and dark solitons is studied via the numerical calculation: (1) Amplitudes of the bright and dark solitons are not related to the coefficient \(\delta _{4}(t)\), while the soliton velocities are related to \(\delta _{4}(t)\). (2) Interactions between the bright two solitons are shown to be elastic, while interactions between the dark two solitons could be elastic or inelastic, which is determined by the values of \(\rho \). (3) Numerical calculation indicates that the bright solitons could not resist the disturbance of small perturbations, while the dark solitons could resist the disturbance of small perturbations.     

Direct observation of dark excitons in individual carbon nanotubes: inhomogeneity in the exchange splitting

We report the direct observation of spin-singlet dark excitons in individual single-walled carbon nanotubes through low-temperature micro-magneto-photoluminescence spectroscopy. A magnetic field (B) applied along the tube axis brightened the dark state, leading to the emergence of a new emission peak. The peak rapidly grew in intensity with increasing B at the expense of the originally dominated bright exciton peak and became dominant at B>3 T. This behavior, universally observed for more than 50 tubes of different chiralities, can be quantitatively modeled by incorporating the Aharonov-Bohm effect and intervalley Coulomb mixing. The directly measured dark-bright splitting values were 1-4 meV for tube diameters 1.0-1.3 nm. Scatter in the splitting value emphasizes the role of the local environment surrounding a nanotube in determining its excitonic fine structure.     

Analysis of characteristic X-ray generation induced by laser plasma electrons accelerated by an electric field

The results of experiments devoted to the study of spectral, spatial, and time characteristics of a spectrally bright point x-ray source based on a vacuum diode with a laser-plasma cathode and a titanium needle anode with a photon energy approximately equal to 4.5 keV are presented. The experimental results revealed a considerable difference between the electron emission from laser plasma in a strong electric field and the explosive electron emission and demonstrated the effectiveness of laser plasma as an electron source. The optimization of the laser radiation power density, the accelerating voltage, and the interelectrode spacing made it possible to create a point x-ray source whose spectral brightness exceeds available sources in the class of small-size pulse x-ray instruments (tubes with explosive cathodes). It has been proved experimentally that the maximum contrast of the characteristic lines of the anode material is attained in the case of an optimal choice of accelerating voltage. The x-ray source has the following parameters: (1) spectral brightness of the K-lines of titanium of the order of 10²¹ photons/cm² s sr keV; (2) emitting region size of 250 mm; and (3) laser pulse duration less than 20 ns.