蓝光激发红色荧光粉的研究进展及其在白光LED中的应用

蓝光LED芯片激发黄色荧光粉是目前白光LED的主要实现方式,引入红色荧光粉对调整白光LED的显色指数及色温有重要意义。重点介绍和评述了可被蓝光激发且具有宽发射带的硫化物、氮化物、铝酸盐等几种体系红色荧光粉的发光性质、最新研究成果及在白光LED中的应用。对比发现,氮化物荧光粉可被从近紫外到可见绿光有效激发,随基质组成的不同,可发出峰值波长为600～650nm的红色荧光,且由于其优良的化学稳定性、热稳定性成为最有前途的一类红色荧光粉。采用两种以上的荧光粉代替单一黄色荧光粉,有利于调整白光LED的色温,提高显色指数。     

One-step synthesis of yellow-emitting carbogenic dots toward white light-emitting diodes

We report herein the synthesis of carbogenic dots (CDs) by a one-step pyrolysis from N-acetylcysteine. The as-prepared CDs show excellent dispersibility with particle sizes in the range of 3–5 nm. Under stimulation with blue light, the CDs emit broad yellow fluorescence, which is still rarely reported by now. The optical properties were throughly investigated, and we found the CDs exhibit stable fluorescence, high quantum yield, and pH dependence. Moreover, an economical approach for constructing white light-emitting diodes (LEDs) was developed by combining the yellow-emitting CDs with blue GaN-based LED chips. The white LEDs exhibit warm white light with the color coordinates of (0.34, 0.35), very close to the coordinates of balanced white-light emission (0.33, 0.33). These results suggest that the CDs can be a promising candidate as yellow-emitting phosphor for white LEDs.     

Novel quantum dots: Water-based CdTeSe/ZnS and YAG hybrid phosphor for white light-emitting diodes

Novel water-based core/shell CdTeSe/ZnS quantum dots (QDs) were synthesized by aqueous method. The CdTeSe/ZnS QDs were investigated by high resolution transmission electron microscopy, energy dispersive spectrometry, UV–vis absorption spectra, and photoluminescence spectrum. The as-prepared QDs capped with ZnS shell were spherical in shape with an excellent quantum yield of 16% and emitted bright yellow light. In addition, the CdTeSe/ZnS QDs can be excited by blue or near-UV region, which is an advantage over wavelength converters for white light-emitting diodes (LEDs). White LEDs based on CdTeSe/ZnS QDs, commercially known as Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce), and hybrid phosphor of CdTeSe/ZnS QDs and YAG:Ce, were fabricated. The luminescent properties of the resultant white LEDs were evaluated. The higher red-component in the emission spectrum from CdTeSe/ZnS QDs increased the color rendering index (CRI) value of the commercial YAG:Ce-based white LEDs, and the hybrid phosphor-based white LED had CIE-1993 color coordinate, color temperature, and CRI values of (0.3125, 0.2806), 7108 K and 83.3, respectively.     

Enhancement of Fluorescence Emission for Tricolor Quantum Dots Assembled in Polysiloxane toward Solar Spectrum‐Simulated White Light‐Emitting Devices

Commercial white light‐emitting diodes (LEDs) have the undesirable characteristics of blue‐rich emission and low color rendering index (CRI), while the constituent quantum dots (QDs) suffer from aggregation‐induced fluorescence quenching and poor stability. Herein, a strategy is developed to assemble tricolor QDs into a polysiloxane matrix using a polymer‐mediated hybrid approach whereby the hybrid composite exhibits a significant enhancement of aggregation‐dispersed emission, outstanding photostability, high thermal stability, and outstanding fluorescence recovery. Using the as‐prepared hybrid fluorescent materials, the fabricated LEDs exhibit solar spectrum‐simulated emission with adjustable Commission Internationale de L'Eclairage coordinates, correlated color temperature, and a recorded CRI of 97. Furthermore, they present no ultraviolet emission and weak blue emission, thus indicating an ideal healthy and high‐CRI white LED lighting source.     

大功率白光发光二极管光源的制作(英文)

采用GaN基蓝色发光芯片为激发源,结合黄色硅酸盐系列荧光粉封装成大功率白光发光二极管(W-LEDs).利用24颗大功率5W白光发光二极管制作了两种不同连接方式的W-LEDs路灯:2并12串,和4并6串.设计了相应的驱动电路,对这两种不同连接方式的大功率W-LEDs路灯的光电特性及其在照明光源中的应用条件作了深入地研究和对比,测试了它们的伏安特性,发光效率以及功效,结果表明2并12串连接方式的W-LEDs路灯具有更加稳定的伏安特性,更高的照度以及更高的功效.与高压钠灯和荧光灯的特性相比较,W-LEDs路灯作为绿色环保光源灯,具有更高的显色指数,更加环保,节能.     

Fabrication of white light-emitting diodes based on UV light-emitting diodes with conjugated polymers-(CdSe/ZnS) quantum dots as hybrid phosphors

White light-emitting diodes (LEDs) were fabricated using GaN-based 380-nm UV LEDs precoated with the composite of blue-emitting polymer (poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-co-(2-methoxy-5-{2-ethylhexyloxy)-1 ,4-phenylene)]), yellow green-emitting polymer (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)]), and 605-nm red-emitting quantum dots (QDs). CdSe cores were obtained by solvothermal route using CdO, Se precursors and ZnS shells were synthesized by using diethylzinc, and hexamethyldisilathiane precursors. The optical properties of CdSe/ZnS QDs were characterized by UV-visible and photoluminescence (PL) spectra. The structural data and composition of the QDs were transmission electron microscopy (TEM), and EDX technique. The quantum yield and size of the QDs were 58.7% and about 6.7 nm, respectively. Three-band white light was generated by hybridizing blue (430 nm), green (535 nm), and red (605 nm) emission. The color-rendering index (CRI) of the device was extremely improved by introducing the QDs. The CIE-1931 chromaticity coordinate, color temperature, and CRI of a white LED at 20 mA were (0.379, 0.368), 3969 K, and 90, respectively.     

Synthesis and luminescence properties of Sr2SiO4: Eu3+, Dy3+ phosphors by the sol-gel method

The Sr2SiO4:Eu3+, Dy3+ phosphors for white light emitting diodes (LEDs) were synthesized by the sol-gel method. The microstructure and luminescent properties of the obtained Sr2SiO4:Eu3+, Dy3+ particles were well characterized. The results demonstrate that the Sr2SiO4:Eu3+, Dy3+ particles, which have spherical morphology, emitted an intensive white light emission under excitation at 386 nm. The phosphors show three emission peaks: the blue emission at 486 nm corresponding to the 4F(9/2)-6H(15/2) transition of Dy3+, the yellow emission at 575 nm corresponding to the 4F(9/2)-6H(13/2) transition of Dy3+, and the red emission at 615 nm corresponding to the 5D0-7F2 transition of Eu3+. At the same time, the effect of Eu3+ concentration on the emission intensities of Sr2SiO4:Eu3+, Dy3+ was investigated in detail. The phosphors used for white LEDs were obtained by combining near ultraviolet (NUV) light (386 nm) with Sr2SiO4:0.04Dy3+, 0.01Eu3+ phosphors with the characteristic of Commission Internationale de l'Eclairage (CIE) chromaticity coordinate (x, y) of (0.33, 0.34), and color temperature Tc of 5,603 K. In addition, the effect of the charge compensators (Li+, Na+, and K+ ions) on the photoluminescence (PL) emission intensities were studied.     

One‐Step Synthesis of Silica‐Coated Carbon Dots with Controllable Solid‐State Fluorescence for White Light‐Emitting Diodes

Carbon dots (CDots)‐based solid‐state luminescent materials have important applications in light‐emitting devices owing to their outstanding optical properties. However, it still remains a challenge to develop multiple‐color‐emissive solid‐state CDots, due to the serious self‐quenching of the CDots in the aggregation or solid state. Herein, a one‐step synthesis of multiple‐color‐emissive solid‐state silica‐coated CDots (silica/CDots) composites by controlling CDots loading fraction and composite morphology to realize the adjustment of emitting color is reported. The emission of resultant silica/CDots composites shifts from blue to orange with the photoluminescence quantum yields of 57.9%, 34.3%, and 32.7% for blue, yellow, and orange emitting, respectively. Furthermore, the yellow emitting silica/CDots composites exhibit an excellent fluorescence thermal stability, and further have been applied to fabricate white‐light‐emitting devices with a high color rendering index of above 80.     

高光效、大功率LEDs/LDs用Ce:YAG透明陶瓷

Ce:YAG透明陶瓷可与蓝光LEDs/LDs复合, 用于大功率白光LEDs/LDs。本研究通过调整Ce:YAG透明陶瓷的厚度和Ce³⁺的掺杂浓度, 将组装器件的发射光谱和色坐标从冷白区调整到暖白区。以高纯(≥99.99%)商业粉体α-Al₂O₃、Y₂O₃、CeO₂为原料, 采用固相反应法制备了(Ce_xY_1-x)₃Al₅O₁₂ (x=0.0005、0.0010、0.0030、0.0050、0.0070和0.0100)透明陶瓷。陶瓷素坯在1750 ℃真空烧结20 h(真空度5.0×10^-5 Pa), 之后在马弗炉中退火1450 ℃×10 h。不同掺杂浓度Ce:YAG陶瓷(厚度分别为0.2、0.4、1.0 mm)在800 nm处的直线透过率均大于79%。Ce:YAG荧光陶瓷的热导率随着测试温度和掺杂浓度的增加而降低。采用有限元方法模拟不同厚度的Ce:YAG陶瓷和LED组装的热分布, 比较了三种封装方式的热分布。将Ce:YAG荧光陶瓷与LEDs/LDs复合, 制备出色坐标分别为(0.3319, 0.3827)和(0.3298, 0.3272)的白光, 发光效率分别为122.4和201.5 lm/W。将Ce:YAG荧光陶瓷和10、50 W商用蓝光LED芯片组合成熟灯具, 可用于商业用途。Ce:YAG透明陶瓷在大功率照明和显示的彩色转换材料应用领域极具潜力。     

Structural and optical characteristics of InN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition

The structural and electrical properties of InN/GaN multiple quantum wells, which were grown by metalorganic chemical vapor deposition, were characterized by transmission electron microscopy (TEM) and electroluminescence measurements. From the TEM micrographs, it was shown that the well layer was grown like a quantum dot. The well layer is expected to be the nano-size structures in the InN multiple quantum well layers. The multi-photon confocal laser scanning microscopy was used to investigate the optical properties of the light emitting diode (LED) structures with InN active layers. It was found that the two-photon excitation was possible in InN system. The pit density was measured by using the far-field optical technique. In the varied current conditions, the blue LED with the InN multiple quantum well structures did not have the wavelength shift. With this result, we can expect that the white LEDs with the InN multiple quantum well structures do not show the color temperature changes with the variations of applied currents.     

Silicon-based oxynitride and nitride phosphors for white LEDs—A review

As a novel class of inorganic phosphors, oxynitride and nitride luminescent materials have received considerable attention because of their potential applications in solid-state lightings and displays. In this review we focus on recent developments in the preparation, crystal structure, luminescence and applications of silicon-based oxynitride and nitride phosphors for white light-emitting diodes (LEDs). The structures of silicon-based oxynitrides and nitrides (i.e., nitridosilicates, nitridoaluminosilicates, oxonitridosilicates, oxonitridoaluminosilicates, and sialons) are generally built up of networks of crosslinking SiN₄ tetrahedra. This is anticipated to significantly lower the excited state of the 5d electrons of doped rare-earth elements due to large crystal-field splitting and a strong nephelauxetic effect. This enables the silicon-based oxynitride and nitride phosphors to have a broad excitation band extending from the ultraviolet to visible-light range, and thus strongly absorb blue-to-green light. The structural versatility of oxynitride and nitride phosphors makes it possible to attain all the emission colors of blue, green, yellow, and red; thus, they are suitable for use in white LEDs. This novel class of phosphors has demonstrated its superior suitability for use in white LEDs and can be used in bichromatic or multichromatic LEDs with excellent properties of high luminous efficacy, high chromatic stability, a wide range of white light with adjustable correlated color temperatures (CCTs), and brilliant color-rendering properties.     

Silicon-based oxynitride and nitride phosphors for white LEDs—A review

As a novel class of inorganic phosphors, oxynitride and nitride luminescent materials have received considerable attention because of their potential applications in solid-state lightings and displays. In this review we focus on recent developments in the preparation, crystal structure, luminescence and applications of silicon-based oxynitride and nitride phosphors for white light-emitting diodes (LEDs). The structures of silicon-based oxynitrides and nitrides (i.e., nitridosilicates, nitridoaluminosilicates, oxonitridosilicates, oxonitridoaluminosilicates, and sialons) are generally built up of networks of crosslinking SiN₄ tetrahedra. This is anticipated to significantly lower the excited state of the 5d electrons of doped rare-earth elements due to large crystal-field splitting and a strong nephelauxetic effect. This enables the silicon-based oxynitride and nitride phosphors to have a broad excitation band extending from the ultraviolet to visible-light range, and thus strongly absorb blue-to-green light. The structural versatility of oxynitride and nitride phosphors makes it possible to attain all the emission colors of blue, green, yellow, and red; thus, they are suitable for use in white LEDs. This novel class of phosphors has demonstrated its superior suitability for use in white LEDs and can be used in bichromatic or multichromatic LEDs with excellent properties of high luminous efficacy, high chromatic stability, a wide range of white light with adjustable correlated color temperatures (CCTs), and brilliant color-rendering properties.     

橙黄光玻璃陶瓷的光固化成型与无压烧结

传统“荧光粉+有机硅脂”荧光转换体的热导率低, 且物理化学稳定性差, 不能应用于高功率白光LED领域。全无机荧光块体材料可以规避有机封装, 具有更高的热导率, 但这类材料面临着成本高且极难实现立体结构的问题。本工作基于非晶态纳米二氧化硅, 得到一种包含(Gd,Y)AG:Ce荧光粉、可在紫外光下固化的浆料, 并通过光固化成型、空气排脂、无压烧结, 制备了一种(Gd,Y)AG:Ce荧光粉-石英玻璃复合材料。该荧光玻璃陶瓷在蓝光激发下发射峰值位于575 nm的宽带橙黄光, 且内量子效率大于90%。研究结果表明, 在致密化烧结过程中, (Gd,Y)AG:Ce荧光粉与石英玻璃之间的界面反应非常微弱, 因此荧光粉能够完好地嵌入到石英玻璃中。该全无机荧光转换体可以用于封装相关色温小于4500 K、显色指数大于75和流明效率为74 lm·W^-1的高功率暖白光LED。所构建的激光照明器件的饱和激光功率密度可达2.84 W·mm^-2, 此时光通量为180 lm。此外, 所提出的制备方法与3D打印兼容, 可以批量化制造出具有复杂立体结构的荧光转换体。该技术有望推动高功率白光LED朝着个性化和模块化发展。     

Ce、Cr∶YAG微晶玻璃的制备及光谱性能研究

目前白光LED在红光波段发射较弱,导致其显色指数偏低,在白光LED用Ce∶YAG微晶玻璃中掺入Cr3+来增强红光波段的发射,从而提高显色指数。通过X射线衍射、荧光光度计、电光源参数测试对样品的晶相、光谱性能及荧光寿命进行了表征。研究了Cr3+对Ce∶YAG微晶玻璃发光性能的影响,并对其增红机理进行了初步的探讨。结果表明基质玻璃在1400℃热处理可析出纯的YAG晶相;Ce∶YAG和Ce、Cr∶YAG微晶玻璃在460nm激发下,在480～650nm产生有效发射,发射光谱中心波长位于530nm;由于Ce3+(2E)-Cr3+(4T)之间的非辐射能量传递,Ce、Cr∶YAG微晶玻璃在688、692和705nm处有红色发射峰,能有效地提高白光LED的显色性能。     

The thermal stability performances of the color rendering index of white light emitting diodes with the red quantum dots encapsulation

Red phosphors are the traditional material used to improve the color rendering index (CRI) of white light emitting diode (WLEDs). In this paper, red quantum dots (QDs) were fabricated and coated on the blue LED chip to replace the red phosphors. By comparing the thermal performances of the CRI for the two WLEDs, we found that WLEDs with the encapsulation of yellow phosphors and red QDs exhibited higher CRI and lower sensitivity to temperature than those with the encapsulation of yellow and red phosphors. The CRI of WLEDs with yellow phosphors and red QDs was 90.9, and its range ability was only 0.3 when the environment temperature changed from 25 °C to 100 °C, while the CRI of WLEDs with yellow and red phosphors was as low as 81.8, and the change of CRI was 2.2 during the same temperature variation.     

Fabrication of silica glass containing yellow oxynitride phosphor by the sol–gel process

We have prepared silica glass by the sol–gel method and studied its ability to disperse the Ca-α-SiAlON:Eu²⁺ phosphor for application in white light emitting diodes (LEDs). The emission color generated by irradiating doped glass with a blue LED at 450 nm depended on the concentration of SiAlON and the glass thickness, resulting in nearly white light. The luminescence efficiency of 1-mm-thick glass depended on the SiAlON concentration, and was highest at 4 wt% SiAlON.     

用于白光LED稀土Eu掺杂SiAlON基荧光粉的发光性能

SiAlON基荧光粉因其优异的化学和物理稳定性,成为近年来发光领域的一个研究热点,尤其在LED等领域,受到研究者的热切关注。稀土掺杂SiAlON基荧光粉体有望成为新一代照明光源。由于缺乏青色光发射,往往会造成显色性能不足。本研究通过传统高温固相法合成了β-Si₅AlON₇:Eu荧光粉,采用X射线衍射仪(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)等研究了其结构、形貌、元素和价态。通过光谱仪表征了样品的激发光谱以及发射光谱的波长范围并测试了热猝灭性能,发现激发波长覆盖紫外至蓝色光区域,并且发射光谱显示出典型的Eu²⁺跃迁的宽谱。在300℃下,样品的发射光强度依然可达到室温强度的40%左右,热激活活化能(E_a)达到了3.7 eV,相比较商用YAG:Ce³⁺(YAG)荧光粉,热稳定性有一定的提升。在与蓝色芯片复合后成功制备了高显色(显色指数R_a=87)的白色发光LED,对应的色温也达到了暖白光范围(CCT=4501K)。本研究实现了SiAlON基青色...     

Fabrication of silica glass containing yellow oxynitride phosphor by the sol–gel process

Abstract

We have prepared silica glass by the sol–gel method and studied its ability to disperse the Ca-α-SiAlON:Eu²⁺ phosphor for application in white light emitting diodes (LEDs). The emission color generated by irradiating doped glass with a blue LED at 450 nm depended on the concentration of SiAlON and the glass thickness, resulting in nearly white light. The luminescence efficiency of 1-mm-thick glass depended on the SiAlON concentration, and was highest at 4 wt% SiAlON.     

Synthesis of Carbon Dots with Multiple Color Emission by Controlled Graphitization and Surface Functionalization

Multiple‐color‐emissive carbon dots (CDots) have potential applications in various fields such as bioimaging, light‐emitting devices, and photocatalysis. The majority of the current CDots to date exhibit excitation‐wavelength‐dependent emissions with their maximum emission limited at the blue‐light region. Here, a synthesis of multiple‐color‐emission CDots by controlled graphitization and surface function is reported. The CDots are synthesized through controlled thermal pyrolysis of citric acid and urea. By regulating the thermal‐pyrolysis temperature and ratio of reactants, the maximum emission of the resulting CDots gradually shifts from blue to red light, covering the entire light spectrum. Specifically, the emission position of the CDots can be tuned from 430 to 630 nm through controlling the extent of graphitization and the amount of surface functional groups, ? COOH. The relative photoluminescence quantum yields of the CDots with blue, green, and red emission reach up to 52.6%, 35.1%, and 12.9%, respectively. Furthermore, it is demonstrated that the CDots can be uniformly dispersed into epoxy resins and be fabricated as transparent CDots/epoxy composites for multiple‐color‐ and white‐light‐emitting devices. This research opens a door for developing low‐cost CDots as alternative phosphors for light‐emitting devices.     

Facile plasma-induced fabrication of fluorescent carbon dots toward high-performance white LEDs

In this study, we report a facile plasma-induced method to fabricate photoluminescent carbon dots (CDs) using acrylamide as the precursor in few minutes. The Fourier transform infrared spectra, UV–Vis absorption spectra, photoluminescence, fluorescent lifetime, and transmission electron microscopy of the as-prepared CDs were investigated thoroughly. The CDs have a narrow size distribution of 3–4 nm and exhibit strong blue fluorescence with quantum yield of ~6 %. More importantly, we explored the CDs as color converters along with CdTe quantum dots to generate white light-emitting diodes (LEDs) using a UV-LED chip as the excitation light source. Compared with the conventional YAG:Ce phosphor-based white LEDs, this resulted LED emitted white light with a higher color rendering index up to 87, which may find their potential in optoelectronic device.