荧光粉配比对大功率白光LED发光特性的影响

利用黄色、红色和黄绿色3种荧光粉混合的方法制备了一系列大功率平面发光LED光源,深入研究了黄色、红色和黄绿色3种荧光粉分别对大功率白光LED光源的发光效率、显色指数以及色温的影响规律。研究结果表明,随着黄色荧光粉含量的增加,其发光效率明显提高,最高可达140 lm/W,而显色指数和色温略有下降。随着红色荧光粉含量的增加,其显色指数明显提高,最高可达85,而发光效率和色温明显降低。随着黄绿色荧光粉含量的增加,其发光效率、显色指数以及色温均不同程度地略有下降,但是其对大功率白光LED的色容差起到很好的调节作用。     

大电流冲击下MEH-PPV对白光LED发光特性的影响

针对用蓝光芯片激发YAG黄色荧光粉实现白光LED的光谱中缺少红色波段成份导致的显色性较差,通过在YAG荧光粉中混合质量分数分别为1%、3%、5%和10%的有机红光材料MEH-PPV,以提高白光LED的显色指数。将制备的白光LED加700mA冲击电流,通过对冲击前后光谱变化的分析结果发现,在大电流冲击下,由于散热不完善,PN结的热阻非常大,导致LED芯片快速老化,并且使有机材料MEH-PPV分解而大量失效;但是对比冲击前后黄光波段的光谱几乎没有变化。这表明,虽然MEH-PPV可以提高器件的显色指数,但是稳定性远不如YAG荧光粉。     

可调色温、显指的前沿白光大功率产品技术分析

白光LED应用在照明领域对其技术参数的要求很高,尤其是室内白光大功率灯具产品对发光效率、色温及显色指数有更高的要求.文章探讨了一种前沿的色温及显色指数可调的技术,通过红光补偿提升显色指数,并通过黄光补偿降低色温,该技术的优势在于显色指数及色温可调的同时,发光效率也有提升.     

大功率LED荧光胶封装工艺对其显色性能的影响

通过大量试验,探索了荧光粉分层封装和荧光粉混合封装的不同荧光胶封装工艺对大功率白光LED显色性能的影响。通过甄选荧光粉、硅胶以及配比,制备出显色指数（CRI）为95的高亮度、低衰减的大功率白光LED。     

大功率LED荧光胶封装工艺对其显色性能的影响

通过大量试验,探索了荧光粉分层封装和荧光粉混合封装的不同荧光胶封装工艺对大功率白光LED显色性能的影响。通过甄选荧光粉、硅胶以及配比,制备出显色指数（CRI）为95的高亮度、低衰减的大功率白光LED。     

高效荧光材料4CzTPN-Ph对LED发光特性的影响

为增强白光发光二极管(LED)的红光成分,通过在Y AG荧光粉中掺杂质量分数分别为1、2、3、7和 11%的高效红色荧光材料4CzTPN-Ph,制备了白光LED,提高 了传统白光 LED的显色指数。分析了4CzTPN-Ph对白光LED参数的影响。结果表明,4C zTPN-Ph可以 被445nm的蓝光激发,掺杂浓度为7%时, 红光峰值最强,同时出现了光谱展宽现象;当掺杂浓度为11%时,显色指数达到87. 3%的最大值。     

低色温高显色性大功率白光LED的制备及其发光特性研究

用GaN基大功率蓝光LED芯片作为激发光源，分别用荧光粉转换法和红光LED补偿法制备了不同相关色温及显色指数的白光LED。对器件的发光特性研究表明，采用监光LED芯片激发单一黄色荧光粉，虽可以获得光通量和发光效率较高的白光LED，但其色温较高，显色性较差；在黄色荧光粉中添加红色荧光粉，由于光谱中红色成分的增加，可降低器件的色温，并提高器件的显色性，但由于目前红色荧光粉的转换效率较低，致使器件的整体发光效率不高；采用蓝光LED芯片激发黄色荧光粉，同时用红光LED进行补偿，通过调整蓝光和红光LED芯片的工作电流以及荧光粉的用量，可获得低色温和高显色性白光LED，而且整体发光效率较高。     

可调色温、显指的前沿白光大功率产品技术分析

白光LED应用在照明领域对其技术参数的要求很高,尤其是室内白光大功率灯具产品对发光效率、色温及显色指数有更高的要求。文章探讨了一种前沿的色温及显色指数可调的技术,通过红光补偿提升显色指数,并通过黄光补偿降低色温,该技术的优势在于显色指数及色温可调的同时,发光效率也有提升。     

低色温高显色性白光LED的研究

文章论述了低色温高显色性白光LED的制备方法及其发展现状与趋势,重点分析了低色温高显色性白光LED的光色电参数．并指出了低色温高显色性白光LED制备技术的难点。同时制备了瓦级大功率白光LED,其显色性高达93,经过1,000小时老化后,色温出现漂移,显色指数仍高于83。     

光谱拟合反演法制备高显色指数白光LED的研究

荧光粉受激发产生的白光LED照明光源存在显色指数较低的问题.对此提出一种利用光谱拟合反演高显指目标光谱的方法,针对已知白光LED计算提高该光源所需补充的单色光LED种类及光谱系数.利用光谱拟合方法分析添加不同波段的光谱对白光LED显指和色温的影响.并通过拟合反演的方法进行补光设计,使用一到两种单色光LED,将冷白光源和中性白光源的显指分别提高至92.3和96.8.实验结果表明,使用红光与蓝绿光、低波长绿光LED补光后,大幅度提高了荧光粉受激发产生的白光LED光源的显色性.     

Luminous efficacy and color rendering index of high power white LEDs packaged by using red phosphor

We packaged a series of high power white LEDs by covering the blue LED chips with yellow phosphor, red phosphor and the two phosphors mixed by appropriate mass ratio,respectively,and discussed the excitation and emission spectrum of yellow phosphor and red phosphor and the characteristics of the LEDs.We found that the luminous efficacy of the white LEDs covered with the two phosphors mixed by appropriate mass ratio was lower than that of the white LEDs covered with yellow phosphor,but the color rendering index was improved observably.     

Luminous efficacy and color rendering index of high power white LEDs packaged by using red phosphor

We packaged a series of high power white LEDs by covering the blue LED chips with yellow phosphor, red phosphor and the two phosphors mixed by appropriate mass ratio, respectively, and discussed the excitation and emission spectrum of yellow phosphor and red phosphor and the characteristics of the LEDs. We found that the luminous efficacy of the white LEDs covered with the two phosphors mixed by appropriate mass ratio was lower than that of the white LEDs covered with yellow phosphor, but the color rendering index was improved observably.     

LiCaPO4:Eu3+材料制备白光LED及其发光特性

采用高温固相法制备了LiCaPO4:Eu3+红色发光材料,研究了Eu3+掺杂浓度、R+或Cl-等对材料发光性质的影响.结果显示,在399 nm近紫外光激发下,材料呈多峰发射,分别由Eu3+的5DO→7FJ(J=0,1,2,3,4)能级跃迁产生,主峰为612 nm;监测612 nm发射峰,所得激发光谱由O2-→Eu3+电...     

Emission from outside of the emission layer in state-of-the-art phosphorescent organic light-emitting diodes

The emission zone profile in an organic light-emitting diode was extracted by fitting the experimentally measured far-field angular electroluminescence spectrum of a purposely designed device. It is based on a thin 10 nm emission layer doped with the red emitting phosphor Ir(MDQ)₂acac. We find strong indications for light emission originating from outside of the emission layer, even though the device has electron and hole blocking layers. These are commonly assumed to completely confine the charge carrier recombination and hence the light emission to the emission layer. Since the calculated internal spectrum of the emission matches the emitter photoluminescence spectrum well, diffusion of the emitter molecules outside of the emission layer is hypothesized.     

Properties of a blue-emitting IR pumped YF3:Yb, Tm diode

A practical blue-light-emitting diode using the IR pumped phosphor YF3:Yb, Tm is described. The emission spectrum of the coated GaAs:Si diode exhibits peaks at 4750, 6450, 7000, 8000, and 9500 Å. Visually, the unfiltered emission appears blue with a purple cast due to the red 6450 Å peak. A luminance as high as 60 fL in the blue has been achieved using reasonable current densities for the pump diode.     

Rare-earth-doped GaN switchable color electroluminescent devices

Switchable color (SC) light emission has been obtained from thin-film electroluminescent devices (ELDs) which use green Er- and red Eu-doped GaN phosphors. These two-electrode SCELDs can switch color through variation of applied bias. Different SCELD structures, which share in common a stacked GaN: Er/GaN: Eu phosphor layer, can be implemented for use with DC or AC operation. A single SCELD can emit green (537/558 nm), red (622 nm), yellow, and orange. For the DC-SCELD, an electrically rectifying GaN/p-Si interface allows polarity-dependent current paths, which induce selective luminescence of red or green phosphor layers. For the AC-SCELD, as the bias frequency is increased, bright red emission from GaN: Eu saturates while green emission from GaN: Er increases and becomes dominant. The AC-SCELD exhibits brightness levels >10 cd/m² and can change chromaticity coordinates by as much as Δx>0.32 and Δy>0.33. Application of these devices to switching between other visible and/or infrared wavelengths is envisioned based on appropriate choice of luminescent dopants in the GaN layers     

YAG:Ce~(3+)玻璃陶瓷白光LED的发光特性

用化学共沉淀法制备掺铈钇铝石榴石(YAG:Ce3+)前驱体,以B2O3-Al2O3-SiO2-Na2O为玻璃基质制作Ce3+掺杂YAG玻璃陶瓷,并封装成玻璃陶瓷白光发光二极管(LED)。改变玻璃陶瓷基片厚度和外形,测量玻璃陶瓷白光LED的光电色参数,并与常规涂敷YAG荧光粉方法制作的白光LED进行对照比较。结果表明,玻璃陶瓷白光LED发射光谱波形与普通白光LED光谱基本一致。玻璃陶瓷基片从0.50mm变化到0.90mm厚时,相关色温(CCT)从4 182 K增加到8862K。0.60mm厚平板玻璃陶瓷基片封装成的白光LED荧光能量转换效率约为20%,中心CCT为6396K,-85°和+85°视角CCT分别为5921K和5898K;而平凸玻璃陶瓷基片封装成的白光LED,-85°和+85°视角CCT变化范围可控制在150K范围内。     

有机荧光材料DCJTB对白光LED发光特性的影响

通过在YAG荧光粉中混合质量分数分别为1％、3％、5％、10％有机材料DCJTB的方法研究白光LED的激发光谱。结果表明,随着DCJTB混合浓度的增加,550-750nm波段的黄光、红光区域有明显的激发波峰,光谱色坐标明显从白光区域（0．2695,0．2435）向红光区域（0．4479,0．2729）移动,但绿光区域光...     

Understanding chromaticity shifts in LED devices through analytical models

This paper demonstrates that chromaticity shifts in light-emitting diode (LED) devices arise from multiple mechanisms that produce chemical changes in the materials used to construct the LED devices. Each chromaticity change is shown to proceed over a finite period of time, and there is a limit on the impact of each shift. For example, chromaticity shifts in LED devices usually start with a fast-acting component that quickly reaches a maximum value, followed by one or more slower acting component(s). This behavior can be modeled analytically with a bounded exponential component to describe the fast-acting component, followed by one or more generalized logistic models. These analytical models contain several key parameters, including the limiting value of each chromaticity shift (A for the upper asymptote and L for the lower asymptote) and the rate of the change k.This approach to chromaticity modeling is demonstrated with analytical models of the chromaticity shifts caused by the irreversible degradation of phosphors. These analytical models provide insights into the kinetic processes responsible for green and red chromaticity shifts caused by phosphor degradation. A green shift is produced by the surface oxidation of the nitride phosphor that changes the emission profile to lower wavelengths. As the surface oxidation reaction proceeds, surface reactants are consumed thereby slowing the reaction rate, and the bulk oxidation processes become more prevalent. A red chromaticity shift can arise from quenching of the green phosphor which shift the emission in the red direction. This paper concludes by discussing the implications of these models for projecting chromaticity for different operational conditions.     

Single-peak excitonic emission of CdSe ultra-thin quantum wells finished with fractional monolayers

Ultra-thin quantum wells (UTQWs) of CdSe grown by atomic layer epitaxy (ALE) present very interesting features, such as intense excitonic luminescence and relatively narrow width. Grown under adequate conditions only a single excitonic peak is exhibited in the photoluminescence (PL) spectrum, indicating the absence of thickness fluctuations. The PL peak of an UTQW grown with the same nominal thickness presents a blue shift if grown at a higher substrate temperature. This energy shift is attributed to changes in composition: instead of a pure CdSe UQTW we obtain a Zn_1?xCd_xSe UTQW with Cd content depending on growth temperature. The fact that even changing the growth temperature only a single excitonic peak is observed is interpreted in terms of a homogeneous mixing of the Cd and Zn atoms at the upper interface. The lack of homogeneity would produce islands and terraces, and then thickness fluctuations that would be clearly evident in the PL spectrum. In order to verify this assertion we have grown UTQWs finished with fractional monolayers, around 0.5 ML of CdSe. We produced UTQWs with 2.5, 3 and 3.5 ML and the result is that all the samples presented a single peak, red shifted with increasing CdSe coverage and monotonic increase in the full-width at half-maximum (FWHM) of the emission. This confirms the homogenization of the CdSe–ZnSe interface.