Development of OLED with high stability and luminance efficiency by co-doping methods for full color displays

We propose co-doping systems in emission layers of red and green organic light-emitting diodes (OLEDs). The luminance-voltage, luminous and power efficiency-voltage characteristics, operational stability, and the energy bands of materials were measured. In red OLED devices, we propose an emitting assist (EA) dopant for better luminance efficiency and power efficiency with pure red emission and improved operational stability. The EA dopant (rubrene) did not emit itself but assisted the energy transfer from a host (Alq) to an emitting dopant (DCJTB). By doping rubrene, the luminance efficiency increased from 1.7 to 4.3 cd/A (from 0.6 to 1.9 lm/W) with chromaticity of (x=0.64, y=0.36) unchanged. An improved lifetime was also observed. In green OLED devices, we introduced hole transporting material (NPB) into an emission layer for better charge injection balance. The green devices with the emitting dopant (C545T) achieved the luminance efficiency of 8.5 cd/A compared with 6.9 cd/A without NPB. We studied the co-doping methods and use of this approach for active-matrix full color display. The power consumption of white emission at 100 cd/m/sup 2/ was reduced by 32%. The effectiveness of these co-doping methods was demonstrated for practical applications.     

白光LED用几种Eu^2＋激活的红色荧光体的性能

本文对固态照明白光LED用Eu^2＋激活硫化钙、Eu^2＋激活的氮化物和氮氧化物三种高效红色荧光体的物理化学和发光特性进行对比和分析。氮（氧）化物红色荧光体的性能稳定。四种材料适合用作InGaN蓝光LED光转换红色荧光体,和YAG：Ce黄粉组合,使制作的白光LED的显色指数Ra大大提高,有利实现LED普通照明。     

Development of high efficiency GaN-based multiquantum-welllight-emitting diodes and their applications

Highly efficient GaInN-GaN multiple quantum-well (MQW) light-emitting diodes (LEDs) were successfully developed by the low-temperature AlN buffer layer method for metal-organic vapor phase epitaxy (MOVPE). The light-emitting layer of the GaInN-GaN MQW drastically enhances the performance of GaN-based LEDs in terms of the efficiency and spectrums. Flip-chip (FC) type MQW LEDs have been newly developed to increase efficiency in extracting light from the GaN-based crystal to the outside. The luminous intensities of FC type blue and green LEDs are typically 6 and 14 cd, respectively, at 20 mA. The output power of the FC-type LEDs was 14 mW at 20 mA, which was approximately two times higher than that of the conventional face-up type blue LEDs. The external quantum efficiency of blue FC-type LEDs was as high as 20% at 20 mA. New multicolor package was developed using these high performance nitride-based LEDs and commercial AlGaInP-based red LEDs, the color range of which is the largest among other flat panel display devices     

High-efficiency white phosphorescent polymer light-emitting devices

White phosphorescent light emission from polymer light-emitting devices (PLEDs) has been demonstrated. To fabricate the white-emitting PLED, blue phosphorescent polymer (BPP) and red phosphorescent polymer (RPP) were used for the emissive layer, and the emission color was tuned by controlling the concentration ratio of BPP to RPP. The external quantum efficiency of the white-emitting PLED, with CIE coordinates of (0.34, 0.36), was 6.0% at luminance of 100 cd/m/sup 2/. To investigate the emission mechanism in the PLED, its photoluminescence spectrum and transient decay were measured. These experimental measurements indicate that direct excitation of the iridium-complex (Ir-complex) units by carrier trapping is a major excitation process for white-emitting PLED. A 3.6-in full-color display based on the white phosphorescent PLED and color filters was demonstrated.     

Enhanced Near-Field Imaging Contrasts of Silver Nanoparticles by Localized Surface Plasmon

Near-field images of Ag nanoparticles are studied using a near-field scanning optical microscopy (NSOM) operating at illumination mode with blue, green, and red probing lights. The obtained far-field intensity contrast between the nanoparticle and background strongly depends on the sizes of nanoparticles and the wavelength of probing light. Experimental NSOM images supported by theoretical 3-D finite-difference time-domain simulation demonstrate that the intensity contrast is enhanced at wavelength close to the localized surface plasmon resonance (LSPR) peak of the nanoparticle. The abilities to distinguish nanoparticles with different LSPR properties on the same substrate can lead to a material-specific NSOM imaging technique.      

Rare-earth-doped GaN: growth, properties, and fabrication of electroluminescent devices

A review is presented of the fabrication, operation, and applications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs emit light due to impact excitation of the rare earth (RE) ions by hot carriers followed by radiative RE relaxation. By appropriately choosing the RE dopant, narrow linewidth emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out by solid-source molecular beam epitaxy, and a plasma N/sub 2/ source. Growth mechanisms and optimization of the GaN layers for RE emission are discussed based on RE concentration, growth temperature, and V/III ratio. The fabrication processes and electrical models for both dc- and ac-biased devices are discussed, along with techniques for multicolor integration. Visible emission at red, green, and blue wavelengths from GaN doped with Eu, Er, and Tm has led to the development of flat-panel display (FPD) devices. The brightness characteristics of thick dielectric EL (TDEL) display devices are reviewed as a function of bias, frequency, and time. High contrast TDEL devices using a black dielectric are presented. The fabrication and operation of FPD prototypes are described. Infrared emission at 1.5 /spl mu/m from GaN:Er ELDs has been applied to optical telecommunications devices. The fabrication of GaN channel waveguides by inductively coupled plasma etching is also reviewed, along with waveguide optical characterization.     

基于电流和双高斯模型的RGB LED光谱仿真与研究

为了探究电流改变对RGB LED芯片光度学、色度学参数产生的影响以及双高斯模型在不同电流下对RGB LED芯片光学特性的预测准确性。结果表明,随着驱动电流IF的增加,红光光谱向长波方向移动,绿光和蓝光光谱产生蓝移,RGB LED芯片的半高宽呈线性增加。不同电流下,双高斯模型拟合得到的光谱与实测光谱接近,红色芯片拟合光谱与实测光谱的相关系数最高为0.993257,绿色为0.994372,蓝色为0.992654,色品坐标(x,y)误差均在3%以内。RGB LED混合高、低色温白光,拟合光谱与实测光谱的相关系数在0.984267以上,拟合色坐标与实测色坐标接近。双高斯模型适用于不同电流下RGB LED混合白光设计,具有一定的理论指导和实践依据。     

基于虚拟仪器的彩色图像单色背景透明化处理

在图片的合成应用中需要对图片进行局部的透明化处理。提出了通过虚拟仪器技术,对具有单色背景的彩色人物图像进行处理的一种算法研究。通过将彩色图像的每个像素点分解成RGB三基色后与提取的特征点比对,对每个像素点灰度值运算构建新的图像掩码集,来重构原图像,完成对原彩色图像背景的透明化处理过程。该方法可以应用与背景颜色较为单一并且与人物图像颜色差异性大的图片处理,效果显著。     

铁路灯光信号颜色的安全理论

信号是通过预先约定好的方式给使用者的信息。铁路信号是给行车人员的命令。本文只谈稳定灯光信号颜色的显示。现行铁路灯光信号显示是用不同颜色灯光或灯光组合给出不同的命令。 目前铁路上使用的信号灯光颜色有红、黄、绿、蓝、白五种，即所谓的五色制。灯光颜色规定的意义，构成显示命令要预先约定好，本文介绍这种规定或约定的根据是以及它与运输安全的关系。     

Spectroscopic study of red light emission in porous silicon

Since bulk silicon does not emit light in the visible part of the spectrum, the discovery of visible luminescence from porous silicon has been quite surprising and has generated significant interest. This material differs from bulk silicon in one important way, in that it consists of interconnected silicon nanostructures, having very large surface to volume ratios. The first emission mechanism proposed involved carrier recombination within quantum size silicon particles, but more recent work has shown that surface emission models may be more likely. The problems with the quantum confinement model will be discussed in view of current data, and an oxygen center luminescence model will be discussed, with supporting experimental data. A direct correlation between the presence of these centers and the red photoluminescence in both as-made and oxidized PSi will be presented     

LED照明灯具在烟草行业节能改造中的应用

LED照明系统带来了一个舒适的照明环境。LED灯无不良眩光、无频闪、显色指数高、照度均匀度高、不同工作环境可应用不同色温以满足工作需要、启动电流小、线路负荷低,固态照明消除了传统照明灯易碎、易爆、有毒等安全隐患;同时LED照明系统节能减排效果显著,在能源日益紧缺的今天,烟厂争做节能改造、绿色环保的实践者!     

Simulating electronic and optical processes in multilayer organic light-emitting devices

A detailed investigation of the device operation of a blue-emitting multilayer organic light-emitting device (OLED) using an electronic device model is presented. In particular, a transient electroluminescence overshoot at turn-on is found to originate from charge and recombination confinement effects at internal interfaces. The location of the emission zone is obtained from the electronic model and its experimental determination exemplified by a sensing layer method. Moreover, the optimization of emission intensity and color is discussed for a red-emitting OLED. The thin-film interference effects are analyzed with help of an optical device model.     

LED照明调光装置设计与实现

采用单片机控制三路D\A转换输出,对LED红、绿、蓝三基色进行调节,实现对半导体照明色彩和亮度宽范围、高精度的调节,同时通过串并转换扫描方式使一套系统可对多个LED分别控制,实现其在高精度控光和控色的基础上可组成任意的静、动态图案或画面。     

LED光谱特性及其在中间视觉下的应用

为了研究中间视觉下LED的光度特性,运用LED光色电综合分析仪测量了不同电流下五种颜色多个LED的光谱,然后计算了不同中间视觉亮度下的光通量,并分析和研究了中间视觉修正系数Rm随电流和亮度的变化。研究表明:电流在12～24mA范围内,同一颜色LED的相对光谱整体变化小于8%,因此在普通照明要求下,可以用平均光谱来描述LED的相对光谱。在中间视觉下,绿、白这两种颜色LED的中间视觉修正系数Rm的对数与亮度的对数存在线性关系,红、黄、蓝LED的Rm的对数与亮度的对数存在二次曲线关系。其中,蓝、绿、白LED的Rm随亮度增大而减小,红、黄LED的Rm随亮度增大而增大。该研究为中间视觉下LED灯具的设计提供了理论基础。     

Red, green, and blue LEDs for white light illumination

The rapid improvement of the white light efficacy achievable with light-emitting diodes (LEDs) opens up new opportunities in the general illumination market. An LED light source made of red, green, and blue LEDs (RGB-LEDs) can provide the unique feature of color variability, allowing the user to select the desired color point of the lamp. The white light color accuracy required in the general illumination market is a challenge for LEDs. The variation in lumen output and wavelength for nominally identical LEDs and the change in these parameters with temperature and time result in an unacceptably high variability in the color point of white light from RGB-LEDs. In this paper, we show that these problems can be overcome with suitable feedback control schemes that can be implemented in a practical LED lamp. We present results of experiment and theoretical modeling that shows the performance that can be achieved with a number of different control schemes     

Light-emitting porous silicon: materials science, properties, anddevice applications

Silicon-based, light-emitting devices (LED's) should find numerous uses in optoelectronics. For example, the integration of silicon LED's with silicon microelectronics could lead to reliable and inexpensive optical displays and optical interconnects. Until recently, however, it had not been possible to obtain efficient room-temperature luminescence from silicon. The demonstration in 1990 that a form of silicon called “porous” can emit bright photoluminescence in the red region of the spectrum triggered worldwide research efforts aimed at establishing the mechanisms for the unexpected luminescence and at fabricating efficient and durable LED's. In less than five years, significant progress has been achieved on both fronts, LED's emitting throughout the visible spectrum have been demonstrated, and the best measured external electroluminescence efficiency has risen from 10^-5% to ~0.01% at room temperature. The photoluminescence efficiency of the best samples is near 10% at room temperature, and light-emitting porous silicon (LEPSi) that luminesces from the blue part of the spectrum to the infrared beyond 1.5 μm has been produced. In this article, we first review why silicon is a poor light emitter and then define porous silicon and its main properties. We then focus on the properties of the three luminescence bands (“red,” “blue,” and “infrared”) and present the results of femtosecond time-resolved optical measurements. Next, we report progress toward the fabrication of LED's and discuss some specific device structures. Finally, we outline what is necessary for commercial LEPSi LED's to become a reality and report on experimental results that suggest the possible integration of LEPSI with standard microelectronic devices     

Polymer thermosetting organic light-emitting devices

We report a systematic study of novel single- and double-layer thermosetting light-emitting devices (LED's) based on triarytamines for hole transport layer and fluorenes for the emitting and electron transport layer. These devices possess high-thermal stability, high-quantum efficiency, and high-bandgap emission (blue and green). We have fabricated dot matrix displays based on analogs of these materials     

荧光粉在高显色白光LED中的应用技术研究

采用蓝光LED芯片作为激发光源,通过封装试验研究了荧光粉发射波段、蓝光芯片波段、白光LED色温和显色指数的关联性。在分析单一组分荧光粉制作的白光LED的基础上,进一步对双组分荧光粉方案进行了试验研究。结果表明当采用绿光荧光粉配合橙黄光荧光粉的双组分方案后,在光效较普通白光LED下降幅度小于15％的情况下,显色指数Ra得到显著提升（86．7）。     

Oxynitride/nitride phosphors for white light-emitting diodes (LEDs)

Oxynitride/nitride phosphors have attracted significant attention recently because they have promising luminescence properties and superior thermal and chemical stabilities which predestinates them for use in white LEDs to generate white light. This paper reports on luminescence spectra of Eu²⁺ or Ce³⁺-activated α-SiAlON, β-SiAlON, and alkaline earth silicon nitride (M₂Si₅N₈, M = Ca, Sr, Ba). A single broad emission band is observed for all samples, and the emission color depends on the type of activators and host lattice: α-SiAlON:Ce³⁺ (blue), α-SiAlON:Eu²⁺ (yellow), β-SiAlON:Eu²⁺ (green), and M₂Si₅N₈:Eu²⁺ (red). The excitation spectrum of these oxynitride/nitride phosphors covers a wide range from ultraviolet to visible light, enabling them to be used for white LEDs when an ultraviolet or blue LED chip is combined.     

远程荧光LED器件影响因素研究

远程荧光技术是传统LED封装散热不良问题的解决方法之一。本文用红色和黄色荧光粉以及光固化树脂,通过光同化方式制备了荧光转换膜,并制备了简单的远程白光LED器件,研究了荧光粉组成、芯片与荧光转换膜的距离及输入电流对远程自光LED器件光学特性的影响,实验结果表明,荧光粉的组成比例对显色指数,色温等都有影响,而荧光转换膜与芯片的距离以及输入电流对器件的光学特性影响不大。本实验还通过添加光扩散剂解决了白光LED芯片发光刺眼问题。研究结果可为新型白光LED的结构设计提供参考。