Light Emitting Diodes as a Rapid Visual Display for Use in Psychological Experiments

In this paper we show how light emitting diodes (LEDs) can be used in conjunction with existing display technologies as a means for achieving ultra-rapid visual stimulus exposure durations. We review existing rapid visual display methods, and show how our apparatus overcomes the limitations inherent with each technique. Our apparatus, the LED tachistoscope, takes advantage of the fast-switching times and high-brightness capabilities of LEDs in order to present stimuli at previously unachievable durations as rapid as 1 ms. The rapid exposure durations are achieved by external LED backlight illumination of images on a liquid crystal display (LCD) after the components of the LCD have stabilized. This ensures that stimulus onset and offset are discrete. Furthermore, the fast-switching of the LEDs enables stimuli to be revealed for very rapid durations. The paper also describes studies in which the LED tachistoscope has already been applied, and offers suggestions for other possible applications. Interestingly, in our studies we show that the human visual system is very adept at extracting information with only very minimal stimulus exposure durations. Such studies have not been possible with existing display equipment. The LED tachistoscope opens up avenues for a variety of psychological and physiological experiments and provides a means for revealing the limits of human visual perception.

Effects of Light-Emitting Diode (LED) Red and Blue Light on the Growth and Photosynthetic Characteristics of <i>Momordica charantia</i>L.

With andromonoecious Momordica charantia L. (bitter gourd) as material, three light qualities (50 μmol·m-2·s-1) including white LED light (WL), blue monochromatic light (B, 465 nm), and red monochromatic light (R, 650 nm) were carried out to investigate their effects on seed germination, physiological and biochemical parameters, sex differentiation and photosynthetic characteristics of bitter gourd. The results showed that compared to the WL treatment, the R treatment significantly promoted seed germination, seedling height elongation and soluble sugar content, the B treatment significantly increased seedling stem diameter, reducing sugar content and soluble protein content, the R and B treatments both significantly reduced sucrose content, but their POD activity showed no significant difference. Compared with the R treatment, the B treatment significantly increased the total female flower number and female flower nod ratio in 30 nods of main stems. The study of photosynthetic characteristics found that the R and B treatments could effectively increase the stomatal conductance (GS) of leaves, significantly improved the net photosynthetic rate (Pn) compared to the WL treatment, and the effect of the B treatment was better. Compared to the R and WL treatments, the B treatment increased the maximum photosynthetic rate (Pmax), apparent quantum efficiency (AQE) and light saturation point (LSP), and reduced the dark respiration rate (Rd) and light compensation point (LCP) of the leaves. Fit light response curves showed that the adaptability and utilization of weak light in bitter gourd were middle or below, but it showed higher adaptability and utilization of strong light. Thus, it suggests that Momordica charantia is a typical sun plan with lower Rd. In summary, it is concluded that blue light has a positive effect on the seed germination, seedling growth, sex differentiation and improving the photosynthetic performance, and this will lay the foundation for artificially regulating optimum photosynthesis using specific LEDs wavelength, and help to elucidate the relationship how light quality influences the sex differentiation of plant.

UV-LED表面消毒辐射场的数学模拟体系的建立及试验验证

为了实现紫外发光二极管(Ultraviolet Light-Emitting Diodes,UV-LED)表面消毒器设计的优化、高效、智能化目的,研究建立了UV-LED表面消毒辐射场的数学模型,并进行了试验验证。根据该数学模型,编写了VBA(Visual Basic for Applications)程序,对辐射场进行了模拟和分析。结果显示,辐射模型的计算值与实测值接近,试验验证了辐射模型的可行性。试验进行了应用举例,当照射距离与灯间距的比值为0.4时,选择最大发光角90°的UV-LED可使辐射场最优化;当照射距离与灯间距的比值为0.8和1.6时,对应的最优选择分别是45°和30°的UV-LED。数学模型和相关计算方法为优化设计紫外线表面消毒设施提供了模拟、优化的有效工具。

OCC系统目标LED阵列解码算法研究

针对强日光环境下OCC(Optical Camera Communication)系统接收端解码困难的问题,提出了基于分段式线性灰度变换的Gradient-Harris解码算法。首先搭建一套OCC实验系统,接收端相机采集原始图像,利用标准相关系数匹配方法提取目标LED阵列区域。其次通过分段式线性灰度变换对目标LED阵列区域进行图像增强,利用Gradient-Harris解码算法进行目标LED阵列的形状提取和状态识别。实验结果表明,应用基于分段式线性灰度变换的Gradient-Harris解码算法,强日光环境下OCC实验系统的平均解码速率为128.08 bit/s,平均误码率为4.38×10^(-4),最大通信距离为55 m。

不同光质配比的LED光源补光对水稻机插秧苗生长发育的影响

以甬优12和扬两优6号作为试验材料,育秧期间采用纯蓝LED光源、纯红LED光源及红蓝光质各50%配比光源补光,以自然光下育秧为对照,研究不同红蓝光质配比LED光源补光对水稻机插秧苗生长发育的影响。结果表明,不同光质配比的LED光源补光对水稻秧苗生长有显著影响。蓝光能够抑制幼苗株高,提高充实度和根冠比,在培育壮苗方面发挥重要作用。红光处理下的水稻幼苗茎和叶鞘显著伸长,秧苗生长进程加快。此外,参试2个品种经红蓝光处理后的幼苗叶龄显著提高。试验结果探明了使用LED补光处理对水稻幼苗形态的影响,为调控水稻工厂化育秧的光环境提供了科学依据。

沿黑体辐射线类太阳光LED调光系统调配及优化

为了使发光二极管(LED)光源光谱在可见光波段更接近太阳光光谱,且相关色温实现沿黑体辐射线连续可调,选取不同峰值波长LED芯片及荧光粉,覆盖可见光波段;采用相应LED芯片激发相应荧光粉,获得多个调光光源并记录色点及相对光谱;根据光谱叠加性原理,混合光源色点位于调光光源在CIE 1931色坐标图中围成的区域内。对四色光源混合调光进行了系统的调配优化,基于脉宽调制(PWM)调光模式,使用LED驱动模块控制各调光LED的光通量,实现了光源沿黑体辐射线色温可连续调节。模拟与实测结果显示,在常用照明色温2700~6500 K时,LED光源的一般显色指数大于98,且各特殊显色指数均大于90。光谱特性与太阳光类似,填补了LED白光中青光波段的凹陷,去除了短波长蓝光危害。

高增益和多路输出均衡的高效LED驱动拓扑研究

驱动多路并联的发光二极管LED(light-emittingdiode)容易导致各路电流不平衡,为了实现各路LED之间的均流并提高电路效率,提出1种具有多路输出能力的高效率LED驱动电源。采用Boost级联串联谐振变换器的结构实现各路LED之间的均流,并获得较高的电压增益;变压器的漏感抑制了开关管导通时的电流上升速度,实现了开关管的ZCS导通;增加了1个无损缓冲电路减缓开关管关断时的电压上升速度,极大地降低了开关损耗;将变压器的励磁电感设计得足够大,使变压器的损耗降低;在实现软开关的同时,仅需1个开关管,从而降低了电路成本并简化了控制。因此,所提方案在实现均流的同时还能够实现较高的效率和电压增益,且成本较低。详细分析了所提方案电路的工作原理和工作特性,并给出了参数设计的具体流程。最后,搭建了1台输入电压为12 V、两路输出功率为7.9 W的样机,证明了所提方案的可行性。

Review of blue perovskite light emitting diodes with optimization strategies for perovskite film and device structure

Perovskite light emitting diodes(PeLEDs)have attracted considerable research attention because of their external quantum efficiency(EQE)of>20%and have potential scope for further improvement.However,compared to red and green PeLEDs,blue PeLEDs have not been extensively investigated,which limits their commercial applications in the fields of luminance and full-color displays.In this review,blue-PeLED-related research is categorized by the composition of perovskite.The main challenges and corresponding optimization strategies for perovskite films are summarized.Next,the novel strategies for the design of device structures of blue PeLEDs are reviewed from the perspective of transport layers and interfacial layers.Accordingly,future directions for blue PeLEDs are discussed.This review can be a guideline for optimizing perovskite film and device structure of blue PeLEDs,thereby enhancing their development and application scope.

Effects of ultrasonic bonding parameters on reliability of flip chip GaN-based light emitting diode

This work applied the ultrasonic bonding to package flip chip GaN-based light emitting diodes （flip chip LEDs） on Si substrates. The effects of ultrasonic bonding parameters on the reliability of flip chip GaN-based LED were investigated. In the sequent aging tests, samples were driven with a constant current of 80 mA for hundreds hours at the room temperature. It was found that the electroluminescence （EL） intensity variation had a large correlation to the ultrasonic power, and then to the bonding temperature and force. A high bonding temperature and ultrasonic power and a proper bonding force improved the EL intensity significantly. It was contributed to a strong atom inter-diffusion forming a stable joint at the bonding interface, The temperature fluctuation in the aging test was the main factor to generate a high inner stress forming delamination at the interface between the chip and Au bump. As a result, delamination had retarded the photons to emit out of the LED packaging and decay its EL intensity.

PEROVSKITE SEMICONDUCTOR OPTOELECTRONIC DEVICES Rational molecular passivation for high-performance perovskite light-emitting diodes

Solution-processed metal halide perovskites (MHPs) have received significant interest for cost-effective, high-performance optoelectronic devices. In addition to the great successes in photovoltaics, their excellent luminescence and charge transport properties also make them promising for light emitting diodes (LEDs). To achieve high-efficiency perovskite LEDs (PeLEDs), extensive efforts have been carried out to enhance radiative recombination rates by confining the electrons and holes. In addition to enhancing radiative recombination rates, it is equally important to decrease the non-radiative recombination for improving the device performance. Passivation of the defects could be an efficient way for reducing the non-radiative recombination.

基于无源均流的谐振式无桥型Boost LED驱动电源

传统Boost功率因数校正变换器的输出电压必须大于输入电压,在一定程度上限制了其在LED驱动电源中的应用。同时,传统LED驱动电源因输入端整流桥的存在而限制了自身效率的进一步提升。基于谐振式Boost功率因数校正变换器拓扑提出了一种无源均流型无桥Boost LED驱动电源,通过引入谐振式电容均流网络,实现了多路均流输出;通过整流桥的去除,进一步提升了系统的效率。最后,搭建了一台效率可达93.64%的140 W实验样机,验证了理论分析的正确性与可行性。

一种新型两开关无电解电容LED驱动电路

LED驱动电源通常需要大电解电容来减少低频电流纹波,电解电容的短寿命是制约LED驱动电源寿命的重要因素,消除电解电容是LED驱动电源长寿命的关键。为此,提出了一种基于反激变换器的两开关无电解电容LED驱动电路拓扑,将辅助功率平衡电路与反激变换器集成,通过2个开关管实现瞬时输入功率与输出功率的平衡,消除电解电容,抑制输出电流低频纹波,实现高功率因数。详细分析了该拓扑的工作原理,并提出了一种适用于该电路拓扑的控制策略。最后搭建了1台30 W的原理样机,实验结果验证了该拓扑的可行性。

Structure and luminescence of Ca_2Si_5N_8:Eu^(2+) phosphor for warm white light-emitting diodes

We have synthesized Ca2Si5N8：Eu^2＋ phosphor through a solid-state reaction and investigated its structural and luminescent properties. Our Rietveld refinement of the crystal structure of Ca1.9Eu0.1Si5N8 reveals that Eu atoms substituting for Ca atoms occupy two crystallographic positions. Between 10 K and 300 K, Ca2Si5N8：Eu^2＋ phosphor shows a broad red emission band centred at -1.97 eV-2.01 eV. The gravity centre of the excitation band is located at 3.0 eV 3.31 eV. The centroid shift of the 5d levels of Eu^2＋ is determined to be -1.17 eV, and the red-shift of the lowest absorption band to be - 0.54 eV due to the crystal field splitting. We have analysed the temperature dependence of PL by using a configuration coordinate model. The Huang-Rhys parameter S = 6.0, the phonon energy hv = 52 meV, and the Stokes shift △S = 0.57 eV are obtained. The emission intensity maximum occurring at -200 K can be explained by a trapping effect. Both photoluminescence （PL） emission intensity and decay time decrease with temperature increasing beyond 200 K due to the non-radiative process.

Performance improvement of blue InGaN light-emitting diodes with a specially designed n-AlGaN hole blocking layer

Blue InGaN light-emitting diodes （LEDs） with a conventional electron blocking layer （EBL）, a common n-A1GaN hole blocking layer （HBL）, and an n-A1GaN HBL with gradual A1 composition are investigated numerically, which involves analyses of the carrier concentration in the active region, energy band diagram, electrostatic field, and internal quantum efficiency （IQE）. The results indicate that LEDs with an n-AIGaN HBL with gradual AI composition exhibit better hole injection efficiency, lower electron leakage, and a smaller electrostatic field in the active region than LEDs with a conven tional p-A1GaN EBL or a common n-A1GaN HBL. Meanwhile, the efficiency droop is alleviated when an n-A1GaN HBL with gradual A1 composition is used.

High-Sensitivity Ozone Sensing Using 280 nm Deep Ultraviolet Light-Emitting Diode for Detection of Natural Hazard Ozone

Recently ozone is one of natural hazards which comes from cars, industry using ozone for sterilization of organic and inorganic materials and for water purification. So, ozone sensing becomes very important, and convenient and accurate ozone sensor is required. A new high sensitivity ozone sensing system using an deep ultra-violet light emitting diode (DUV-LED) operated at the wavelength of 280 nm has been successfully constructed. The fabrication of diode operated at 280 nm is much easier than that of DUV-LED operated at Hg lamp wavelength of 254 nm. The system is compact and possible to sense the ozone concentration less than 0.1 ppm with an accuracy of 0.5% easily with low power DUV-LED of around 200 micro Watts operated at 280 nm without any data processing circuit.

Enhancement in Light Extraction Efficiency of GaN-Based Light-Emitting Diodes Using Double Dielectric Surface Passivation

SiO2Al2O3 double dielectric stack layer was deposited on the surface of the GaN-based light-emitting diode (LED). The double dielectric stack layer enhances both the electrical characteristics and the optical output power of the LED because the first Al2O3 layer plays a role of effectively passivating the p-GaN surface and the second lower index SiO2 layer increases the critical angle of the light emitted from the LED surface. In addition, the effect of the Fresnel reflection is also responsible for the enhancement in output power of the double dielectric passivated LED. The leakage current of the LED passivated with Al2O3 layer was -3.46 × 10-11 A at -5 V, at least two and three orders lower in magnitude compared to that passivated with SiO2 layer (-7.14 × 10-9 A) and that of non-passivated LED (-1.9 × 10-8 A), respectively, which indicates that the Al2O3 layer is very effective in passivating the exposed GaN surface after dry etch and hence reduces nonradiative recombination as well as reabsorption of the emitted light near the etched surface.

紫外发光二极管(UV-LED)技术对食品微生物灭活应用的研究进展

紫外辐照是一种非热杀菌技术,汞蒸气紫外灯是现阶段用于食品卫生处理的主要设备,但受某些因素影响,汞灯的生产使用将逐渐变少,被环保节能的紫外发光二极管(UV-LED)取代是一种不可避免的趋势。本文根据UV-LED发光原理和多波长耦合应用的特点,综述了对微生物灭活的机理、探究了影响灭活效果的因素(波长、紫外剂量和物料特性)、处理食品的灭菌效果以及对部分食品品质的影响,为UV-LED在食品领域的杀菌处理工艺和设备参数优化提供参考。

Double superlattice structure for improving the performance of ultraviolet light-emitting diodes

The novel AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) with double superlattice structure(DSL) are proposed and demonstrated by numerical simulation and experimental verification. The DSL consists of 30-period Mg modulation-doped p-AlGaN/u-GaN superlattice(SL) and 4-period p-AlGaN/p-GaN SL electron blocking layer, which are used to replace the p-type GaN layer and electron blocking layer of conventional UV-LEDs, respectively. Due to the special effects and interfacial stress, the AlGaN/GaN short-period superlattice can reduce the acceptor ionization energy of the ptype regions, thereby increasing the hole concentration. Meanwhile, the multi-barrier electron blocking layers are effective in suppressing electron leakage and improving hole injection. Experimental results show that the enhancements of 22.5%and 37.9% in the output power and external quantum efficiency at 120 m A appear in the device with double superlattice structure.

Design of patterned sapphire substrates for GaN-based light-emitting diodes

A new method for patterned sapphire substrate （PSS） design is developed and proven to be reliable and cost-effective. As progress is made with LEDs＇ luminous efficiency, the pattern units of PSS become more complicated, and the effect of complicated geometrical features is almost impossible to study systematically by experiments only. By employing our new method, the influence of pattern parameters can be systematically studied, and various novel patterns are designed and optimized within a reasonable time span, with great improvement in LEDs＇ light extraction efficiency （LEE）. Clearly, PSS pattern design with such a method deserves particular attention. We foresee that GaN-based LEDs on these newly designed PSSs will achieve more progress in the coming years.