荧光粉涂覆方式对白光LED光色指标的影响

文章采用TRACEPRO软件建立了三种白光LED的光学模型:(1)芯片直接涂覆荧光粉;(2)芯片涂覆硅胶后涂覆荧光粉层;(3)芯片涂覆荧光粉后涂覆硅胶层.通过改变荧光粉的摩尔浓度或硅胶厚度来考察白光LED的光色指标,如光通量、色温及显色指数的变化.研究结果表明:第一种和第二种涂覆方式中,光色指标随着荧光粉摩尔浓度或硅胶厚度的改变呈规律性变化;第三种涂覆方式中,色温及显色指数的变化趋势不稳定,第三种方式光通量高于前两种,最大值可达到87.31m.三种方式的显色指数在70左右.研究结论为白光LED工艺设计提供参考和依据.     

台湾研制成功量子点白光LED

台湾工业技术研究所已研制成功一种基于量子点的白光发光二极管(LED)。研究人员通过将一种混合有机分子覆盖在多面体ZnSe量子点上形成冠状结构,并采用紫外辐射激励的量子点,从而获得了白光LED。     

基于Ⅱ-Ⅵ族半导体量子点的白光LED的研究进展

作为发光可覆盖整个可见光波段的发光材料,Ⅱ-Ⅵ族半导体量子点自上世纪90年代以来一直是构筑白光发光二极管（LED）的关键材料之一。本文主要介绍基于缺陷态发光、单源二色互补发光、三基色复合发光和光致发光等发光原理的半导体量子点的白光LED,并比较了不同类型器件的特点。凭借发光效率等主要性能参数的优势,基于GaN基蓝紫光与量子点荧光粉组合得到的白光LED将最有可能首先实现商业化应用。而在高清显示技术方面,结合微接触印刷技术的三基色复合白光LED具有潜在应用价值。最后简要介绍在提高白光LED发光效率方面的进展。     

台湾研制成功量子点白光LED

台湾工业技术研究所已研制成功一种基于量子点的白光发光二极管（LED）。研究人员通过将一种混合有机分子覆盖在多面体ZnSe量子点上形成冠状结构，并采用紫外辐射激励的量子点，从而获得了白光LED。     

荧光层形状对大功率白光LED光学性能的影响

为确定荧光层形状对大功率白光LED光学性能的影响,对蓝光LED发光晶片激发黄色荧光粉产生白光的荧光涂布工艺进行了研究。分别通过大面积点胶、晶片表面点胶和保形荧光胶涂布工艺制得白光LED样品,利用积分球和角度测试机对白光LED的光学性能进行测试,结果表明,保形荧光层白光LED的色温、光强分布和发光角度等光学性能优于大面积点胶和晶片表面点胶白光LED的光学性能。     

全自动荧光粉涂覆工艺研究

自行设计并搭建了一套全自动荧光粉涂覆系统。针对涂覆工艺,通过扫描电子显微镜研究真空搅拌除泡处理时间对涂覆质量的影响,结果发现未经真空搅拌除泡处理的荧光粉涂覆层中有直径达140μm的气泡,且涂覆层厚度均匀性较差;经过20和40 s真空搅拌除泡处理后涂覆层中气泡直径和数量都明显减少,涂覆层厚度均匀性也变好;经过60 s真空搅拌除泡处理后涂覆层中无明显气泡,涂覆层厚度均匀性进一步提高至1μm。分别不通过真空搅拌除泡处理和通过60 s真空搅拌除泡处理实现LED器件涂覆,通过LED器件光学参数综合测试仪测试上述两类器件的发光特性,结果发现60 s真空搅拌除泡处理能明显降低LED器件色坐标的离散性。     

无机钙钛矿CsPbX3量子点发光材料及器件的研制

全无机钙钛矿量子点是非常具有发展潜力的发光材料,其中CsPbX3(X为C1、Br和I)因其具有非常窄的发光峰、较好的稳定性以及可以在溶液中制备等优点,受到了研究人员的重点关注.文章在室温下根据过饱和析出原理制备了不同卤族元素配比的全无机钙钛矿量子点,该制备方法不需要惰性气氛保护和热注入,量子点的合成可以在几秒内完成.通过光致发光光谱、吸收光谱、X射线衍射等分析方法研究了不同配比CsPbX3量子点的结构特征和光致发光特性.将CsPbX3量子点涂覆在蓝光发光二极管芯片表面实现了器件的白光发射,并分析了其光谱特征.     

国际视点

<正>技术量子点照亮未来照明随着白炽灯泡时代的迅速衰退,取而代之的是一种可产生高品质白光的高效固态照明设备。白光量子点就是选择的技术之一,其可产生纯白色的光。超小型的硒化镉荧光珠,可将LED发出的蓝光转换为温暖的白光,其光谱类似于白炽灯。对应地,紧凑型荧光灯管和大多数白光LED发出的都     

LED合成光谱光源色度参数的快速计算及应用

为满足色彩还原的需要,白光LED照明光源通常用光谱合成的方法获得连续的宽光谱。各频段的光谱分量与光源最终色度参数的关系以及它们比例的确定通常由实验得出。因而目前光源的设计是一个极其复杂的尝试过程,对实验要求高、周期长、投入大。对LED合成光谱白光照明光源的色参数进行了系统的分析,依据LED光源相关标准测量方法,推导出了LED合成光谱白光光源色度参数的快速计算方法,开发了计算机设计分析软件,并通过了设计过程和产品的使用验证。     

两基色白光LED的配色研究

从色度学原理出发,简述了两基色白光LED的配色原理,确定了可合成白光的两基色的选取范围和两基色的配比范围,计算分析了两基色白光LED的光视效能和一般显色指数。两基色白光LED具有较高的光视效能,但其显色性却较差,主波长为450 nm左右的蓝光LED与主波长572 nm左右的黄绿光混合得到的白光的光视效能值最大,约为400 lm/w,已接近等能纯白点的理论极值,但一般显色指数只有—0.5。主波长为480 nm左右的LED与主波长为580 nm左右的LED混合得到的白光的一般显色指数值最大,仅为16.2。     

发光层厚度对基于CdSSe/ZnS量子点LED性能的影响

采用粒径约为10 nm的CdSSe/ZnS量子点层作为发光层,制备了叠层结构的量子点发光器件,研究了量子点层厚度对其薄膜形貌及量子点发光二极管性能的影响.原子力显微镜测试结果表明:量子点层过厚时,量子点颗粒发生团聚,且随着厚度的降低,团聚现象减弱;当量子点层厚度和量子点粒径相当时(约为10 nm),量子点呈单层排列且团聚现象基本消失;而量子点层厚度低于10 nm时,薄膜出现孔洞缺陷.器件的电流-电压-亮度等测试结果表明:量子点发光二极管中量子点层厚度与器件的光电特性密切相关,量子点层厚度为10 nm的器件光电性能最优,具有最低的启亮电压4.2V,最高的亮度446 cd/m2及最高的电流效率0.2 cd/A.这种通过控制旋涂转速改变量子点层厚度的方法操作简单、重复性好,对QD-LED的研究具有一定应用价值.     

Stable White Light‐Emitting Biocomposite Films

The demonstration of reliable and stable white light‐emitting diodes (LEDs) is one of the main technological challenges of the LED industry. This is usually accomplished by incorporation of light‐emitting rare‐earth elements (REEs) compounds within an external polymeric coating of a blue LED allowing the generation of white light. However, due to both environmental and cost issues, the development of low‐cost REE‐free coatings, which exhibit competitive performance compared to conventional white LED is of great importance. In this work, the formation of an REE‐free white LED coating is demonstrated. This biocomposite material, composed of biological (crystalline nanocellulose and porcine gastric mucin) and organic (light‐emitting dyes) compounds, exhibits excellent optical and mechanical properties as well as resistance to heat, humidity, and UV radiation. The coating is further used to demonstrate a working white LED by incorporating it within a commercial blue LED.     

Improvement of lumen efficiency in white light-emitting diodes with air-gap embedded package

In this paper, white light-emitting diodes (LEDs) with air-gap embedded package were proposed and fabricated by a simple method including pulsed spray coating. The lumen efficiency of air-gap embedded LED was enhanced by 8.8% at driving current of 350 mA, compared to conventional remote phosphor white LED. This improvement was due to the enhanced utilization of blue and yellow rays, which were confirmed by pulse current-dependent correlated color temperature (CCT). The utilization efficiency of blue rays was enhanced by 12.4% due to the embedded air-gap layer. The simulation results performed by Monte-Carlo ray tracing method agreed with our experiments, which showed enhancement in lumen efficiency and similar CCT. Finally, the electric field intensity versus different thickness for air-gap and no air-gap embedded white LED was calculated to check the incident blue rays trapped in phosphor layer.     

Optoelectronic properties of heteronanostructures with combined layers of In(Ga)As/GaAs quantum wells and dots

The effect of the incorporation of an InGaAs quantum well into structures with InAs/GaAs quantum dots grown by gas-phase epitaxy on their optoelectronic properties is analyzed in the mode with increased growth-interruption time. It is established that the quantum-dot energy spectrum is weakly sensitive to variations in the thickness and composition of the double InGaAs/GaAs coating layer. The deposition of a quantum well onto a layer of quantum dots decreases the emission-barrier effective height in them. The conditions under which the quantum well can be used for protecting the quantum-dot active layer against penetration by defects generated during structure-surface anodic oxidation are determined.     

Tuning the spectrometric properties of white light by surface plasmon effect using Ag nanoparticles in a colour converting light-emitting diode

We report on the spectral tunability of white light by localized surface plasmon (LSP) effect in a colour converting hybrid device made of CdSe/ZnS quantum dots (QDs) integrated on InGaN/GaN blue light-emitting diodes (LEDs). Silver (Ag) nanoparticles (NPs) are mixed with QDs for generating LSP effect. When the plasmon absorption of Ag NPs is synchronized to the QW emission at 448 nm, the NPs selectively absorb the blue light and subsequently enhance the QD emission. Using this energy transfer scheme, the (x, y) chromaticity coordinates of the hybrid white LED was tuned from (0.32, 0.17) to (0.43, 0.26), and thereby generated warm white light emission with correlated colour temperature (CCT) around 1800 K. Moreover, a 47% enhancement in the external quantum efficiency (EQE) was realized.     

Solvent‐Polarity‐Engineered Controllable Synthesis of Highly Fluorescent Cesium Lead Halide Perovskite Quantum Dots and Their Use in White Light‐Emitting Diodes

Cesium lead halide quantum dots (QDs) have tunable photoluminescence that is capable of covering the entire visible spectrum and have high quantum yields, which make them a new fluorescent materials for various applications. Here, the synthesis of CsPbX₃ (X = Cl, Br, I, or mixed Cl/Br and Br/I) QDs by direct ion reactions in ether solvents is reported, and for the first time the synergetic effects of solvent polarity and reaction temperature on the nucleation and growth of QDs are demonstrated. The use of solvent with a low polarity enables controlled growth of QDs, which facilitates the synthesis of high‐quality CsPbX₃ QDs with broadly tunable luminescence, narrow emission width, and high quantum yield. A QD white LED (WLED) is demonstrated by coating the highly fluorescent green‐emissive CsPbBr₃ QDs together with red phosphors on a blue InGaN chip, which presents excellent warm white light emission with a high rendering index of 93.2 and color temperature of 5447 K, suggesting the potential applications of highly fluorescent cesium lead halide perovskite QDs as an alternative color converter in the fabrication of WLEDs.     

白光LED的实现及荧光粉材料的选取

主要介绍了目前主流白光LED的封装方法,简述了各种方法的原理及优缺点。重点介绍了蓝光芯片与黄光荧光粉混合实现白光LED的机制。通过测试芯片发射谱、不同荧光粉材料的激发和发射谱,重点研究了蓝色芯片与黄色荧光粉材料的光谱匹配性,讨论了荧光粉材料的选取对器件的电学、光学性能的影响。     

Efficient larger size white quantum dots light emitting diodes using blade coating at ambient conditions

Here, we propose a facile strategy to realize all-solution-processed highly efficient full-color-enabling white emitting quantum dot light-emitting diodes (QLEDs) at ambient conditions by using low-cost blade coating technique, which was also compatible with the roll to roll fabrication process for large size production. Firstly, by using red quantum dots (QDs) as the representative to optimize the QDs films by blade coating, the QDs films exhibit excellent morphology and well-ordered self-assembly structure. Then, the trichromatic white QLEDs based on mixed red, green and blue quantum dots were obtained with Commission Internationale De I'Eclairage (CIE) coordinates ranging from (0.42, 0.41) to (0.31, 0.33) within the white region of CIE 1931 when driving voltage vary from 5 v to 8 v. The device enjoys excellent optoelectronic performance including a maximum luminance of 11,465 cd/m², a maximum current efficiency (η_A) of 9.2 cd/A and an external quantum efficiency (EQE) of 3.7%. In addition, 3 × 8 cm² white QLEDs with bright and homogenous light emission fabricated by blade coating are demonstrated. Our strategy for fabricating large-area white QLEDs indicate promising applications in the low-cost solid-state lighting and flat-panel displays.