High Color-Rendering Index and Stable White Light-Emitting Diodes Based on Highly Luminescent Quantum Dots

Solid-phase color converter-based quantum dots (QDs) white light-emitting diodes (WLEDs) have become promising next-generation solid-state light sources. However, the development of these WLEDs’ production still suffers from constraints involving insufficient color-rendering index (CRI), low color stability, and short operation lifetimes. Here, thick-shell Cd_0.05Zn_0.95S/CdSe/Cd_xZn_1–xS spherical quantum wells are developed with good color tunability from green to red regions and high photoluminescence quantum yield (up to 88% for green wavelengths). QDs with five emission colors are used to fabricate a series of WLEDs, which possess a good correlated color temperature tunability from warm (3210 K) to cool (22 000K) white light, and a high CRI Ra (>90). Specifically, the neutral white light device with Commission Internationale de l´Eclairage (CIE, International Commission on illumination) of (0.36, 0.36) and the standard white light device with CIE of (0.33, 0.33) achieve a CRI Ra up to 95.8 and 95.11, respectively, they also exhibit long operating life and great color stability. These results indicate that the improvement of the performance and stability of the WLED based on thick-shell spherical quantum wells is remarkable progress in the commercialization of QD-based solid-state lighting.     

Warm-white light-emitting diodes integrated with colloidal quantum dots for high luminous efficacy and color rendering

Warm-white LEDs (WLEDs) with high spectral quality and efficiency are required for lighting applications, but current experimental performances are limited. We report on nanocrystal quantum dot (NQD) hybridized WLEDs with high performance that exhibit a high luminous efficacy of optical radiation exceeding 350lm/W(opt) and a high color rendering index close to 90 at a low correlated color temperature <3000K. These spectrally engineered WLEDs are obtained using a combination of CdSe/ZnS core/shell NQD nanophosphors integrated on blue InGaN/GaN LEDs.     

Cesium lead halide perovskite quantum dot-based warm white light-emitting diodes with high color rendering index

White light-emitting diodes (WLEDs) were fabricated by employing a combination of a commercial yellow emission Ce³⁺-doped Y₃Al₅O₁₂ (YAG:Ce)-based phosphor and all-inorganic perovskite quantum dots pumped with blue LED chip. Perovskite quantum dot solution was used as the color conversion layer with liquid-type structure. Red-emitting materials based on cesium lead halide (CsPb(X)₃) perovskite quantum dots were introduced to generate WLEDs with high efficacy and high color rendering index through compensating the red emission of the YAG:Ce phosphor-based commercialized WLEDs. The experimental results suggested that the luminous efficiency and color rendering index of the as-prepared WLED device could reach up to 84.7 lm/W and 89, respectively. The characteristics of those devices including correlated color temperature (CCT), color rendering index (CRI), and color coordinates were observed under different forward currents. The as-fabricated warm WLEDs showed excellent color stability against the increasing current, while the color coordinates shifted slightly from (0.3837, 0.3635) at 20 mA to (0.3772, 0.3592) at 120 mA and color temperature tuned from 3803 to 3953 K.     

植物照明用荧光粉转换白光二极管的研究

LED具有效率高、体积小、功耗低、寿命长等优点,并且因其具有可轻易实现宽幅光谱调控的特性,在植物照明领域崭露头角。植物照明用LED分为两大类,一类是单色光LED,另一类是白光LED,其中植物照明用白光LED可与单色LED混合或者单独使用从而实现植物补光照明。植物封装用白光LED大部分采用蓝光LED芯片或紫外LED芯片和荧光粉组合实现,即荧光粉转换型白光LED,但是光谱集中于可见光偏蓝,对植物进行光合作用的效率不明显。植物对于光的吸收不是全波段的而是有选择性的,基于植物光合作用吸收光谱的特殊性,将白光LED光谱的显色性能作为评判其光谱是否适合植物生长所需的光质的标准,其平均显色指数Ra,特殊显色指数R9(饱和红光),R12(饱和蓝光)被考虑选择为植物照明用白光LED的主要性能评价参数。为设计出植物进行生长发育所需要的、性能良好的能应用于植物照明领域的白光LED,选用常见商用YAGG为绿色颜色转换材料,选用(Sr, Ca)AlSiN₃为红色颜色转换材料,并用传统高温固相法制备了系列光谱可调的(Sr, Ca)AlSiN₃荧光粉,并进行了光谱性能分析。通过将搭建好的LED结构模型导入光学仿真软件并分别引入绿色荧光粉颗粒、红色荧光粉颗粒以及蓝光芯片的特性参数,在Lighttools中分别建立了单蓝光LED芯片(450 nm)和双蓝光LED芯片(450+470 nm)激发(Sr, Ca)AlSiN₃和YAGG荧光粉组合,实现了白光LED的光学仿真模型,研究了两种激发模式下仿真得到的不同色温白光LED的光谱功率分布及其显色性能。用蓝光LED芯片、(Sr, Ca)AlSiN₃以及YAGG荧光粉组合进行了单芯片和双芯片显色性能差异的封装验证。通过将Sr_0.8Ca_0.12AlSiN₃∶0.08Eu2+和YAGG荧光粉的混合物点涂在双蓝光LED芯片上进行了白光LED的封装制备,获得了Ra=91.2,R9=96.1,R12=78.9,光谱辐射光效LER=126 lm·W-1的高效高显色白光LED其含有植物生长所需要的蓝光和红光。     

CaAlSiN_3∶Eu~(2+)荧光粉掺杂PC透光罩的制备及其在植物灯中的应用

为了实现传统白光LED光源与植物照明用光源之间的快速转换,采用高温熔融造粒的方式制备了不同质量分数CaAlSiN_3∶Eu~(2+)(CASN∶Eu~(2+))掺杂的荧光聚碳酸酯(PC)透光罩,并进行了结构和光学分析。制备了荧光PC透光罩配备的T8型LED灯管,测试了其EL光谱、相关光学性质以及对于生菜的种植效果。结果表明,CASN∶Eu~(2+)荧光粉在掺杂过程中性质稳定,该灯管随着配备的透光罩的荧光粉掺杂浓度的提高,相对应的WLED的色坐标从(0.3272,0.3467)变化到(0.3895,0.3824),色温从5757K下降到3807K,显色指数从70.3上升到77.6,但光效略有减弱。配备了荧光粉质量分数为4‰透光罩的T8型白光LED灯管的光质更适合生菜生长。     

White light emission from blue and near ultraviolet light-emitting diodes precoated with a Sr3SiO5:Ce3+,Li+ phosphor

White-light-emitting diodes (WLEDs) were fabricated by combining a yellow Sr3SiO5:Ce3+, Li+ phosphor with a blue light-emitting diode (LED) (460 nm chip) or a near ultraviolet (n-UV) LED (405 nm chip), respectively. Color temperature (Tc) of Sr3SiO5:Ce3+, Li+-based WLEDs could be tuned from 6500 to 100,000 K (blue LED pumping) and from 4900 to 50,000 K (n-UV LED pumping) without mixing with other phosphors. The blue LED-pumped WLED showed excellent white light (luminous efficiency=31.7 lm/W, Tc=6857 K) at 20 mA. This WLED showed a stable color coordinates property against an increase of the forward current. An n-UV LED-pumped WLED also showed bright white light (25.0 lm/W, 5784 K) at 20 mA.     

基于量子点荧光粉白光LED的发光特性和稳定性研究

基于量子点荧光粉白光发光二极管（WLED）是由蓝色GaN芯片和发红光及绿光的CdSe／CdS／ZnS量子点（QDs）组成。因为CdSe量子点的发射波长可在510~620nm之间调节,导致了其色坐标和色差的可变。采用的CdSe量子点是在制备无机前驱体和非配位溶剂的基础上通过合成方法得到的。实验证实温暖和寒冷白光辐射是由于色温在40009000K区间变化;不同的偏置电压导致了颜色坐标的变化,增加工作时间在90min内对白光发射的稳定性进行分析得到稳定光谱。     

Silica encapsulated ZnO quantum dot-phosphor nanocomposites:Sol-gel preparation and white light-emitting device application

ZnO quantum dots(QDs) as an eco-friendly and low-cost material has bright fluorescence, which makes it promising material for healthy lighting and displaying. However, the low fluorescence efficiency and poor stability of ZnO QDs impede their applications in lighting application. In this work, silica encapsulated ZnO QD-phosphors nanocomposites(ZSPN) have been prepared through a sol-gel synthesis process, where yellow-emitting ZnO QDs and blue-emitting BaMgAl_(10) O_(17):Eu~(2+) are employed as the luminescence cores and silica as link between two luminescence materials. Tunable photoluminescence of ZSPN and the white light emission have been achieved through changing mass ratio of both of ZnO QDs and commercial phosphors. The PLQY of the ZSPN can reach 63.7% and they can maintain high luminous intensity even the ambient temperature up to 110?C and after 35 h of UV irradiation. In addition, they can keep stable for 40 days. By coating the ZSPN phosphors onto a ultraviolet chip, WLEDs with luminous efficiency of 73.6 lm/W and the color coordinate, correlated color temperature, and color rendering index can reach(0.32, 0.34), 5580 K, and 87, respectively,indicating the bright prospect of the ZSPN phosphors used in healthy lighting.     

Characteristic white light emission via down-conversion SrGdAlO4:Dy3+ nanophosphor

An efficient and cost-effective technique, solution combustion synthesis was used to synthesize Dy³⁺ doped SrGdAlO₄ nanophosphor utilizing urea as a suitable fuel. The tetragonal phase and nano-crystallinity of the synthesized phosphor belonging to I4/mmm space group was confirmed by powder X-ray diffraction (PXRD) and transmission electron microscope (TEM) technique respectively. Various crystal structure parameters and refined atomic positions of host matrix and SrGd_0.95Dy_0.05AlO₄ nanophosphor were determined by Rietveld refinement. The two intense bands i.e. blue and yellow bands were observed in photoluminescence emission spectrum recorded at 352 nm excitation wavelength, associated to transitions ⁴F_9/2 → ⁶H_15/2 (484 nm) and ⁴F_9/2 → ⁶H_13/2 (575 nm) respectively. Photometric characterizations revealed the emission of white color by the synthesized nanophosphor proving its wide applications in WLEDs (white light emitting diodes). Band gap values calculated using diffuse reflectance spectra (DRS) were found to vary in the range of 5.50 eV–5.59 eV for host and doped lattice system. Keeping in mind, the concentration quenching phenomenon, SrGd_0.95Dy_0.05AlO₄ was considered as optimized nanophosphor for WLEDs.     

Structural,morphological and optoelectronic aspects of YAlO3:Dy3+ doped nanocrystalline materials for NUV energized WLEDs

Cost-effective urea assisted solution combustion (SC) synthetic method was employed to prepare a series of doped YAlO₃:xDy³⁺ (0.01–0.08 mol) phosphors. The resulting powdered samples were comprehensively examined through various structural as well as optical measurements. Rietveld refinement studies concluded that prepared nanomaterials structured into the orthorhombic system having Pbnm (62) space group. Energy dispersive spectral (EDS) analysis was executed to observe the relative proportions of constituent elements in all doped nanophosphors. Transmission electron microscopy (TEM) micrograph indicated the presence of agglomerated particles with the average size in the nano range. Photoluminescence excitation (PLE) spectra showed that the designated phosphors could be excited by near ultraviolet (NUV) energized lighting sources. The strongest emission centred at 576 nm, corresponding to electric dipole (⁴F_9/2 → ⁶H_13/2) transition of Dy(III) ion. Furthermore, characteristics photometric parameters viz. correlated color temperature (CCT), chromaticity coordinates (x and y), and color purity (%) were figure out with the aid of PL data, which strongly endorsed their usage in NUV energized WLEDs applications.     

Warm-white light-emitting diodes integrated with colloidal quantum dots for high luminous efficacy and color rendering: comment

This is a comment on a previous Letter [Opt. Lett.35, 3372 (2010)]. The chromaticity coordinates of nanocrystal quantum dot (NQD)-integrated WLED1, WLED2, and WLED3 are out of the range of the chromaticity tolerance quadrangles of white light sources. So these NQD WLEDs do not satisfy the requirements recommended for general lighting with solid-state lighting products to ensure high-quality white light. Furthermore, correlated color temperatures of WLED2 and WLED3 should be 2682 and 2527 K, respectively, according to the chromaticity coordinates of WLED2 and WLED3 at 12 mA, not 2781 and 2390 K. The NQD-integrated WLED1 and WLED2 located in tolerance quadrangles are simulated by the changing spectral power of green-, yellow-, and orange-emitting NQDs. The simulation results are presented.     

唐代苏同家族墓天王俑彩绘的光谱分析

天王俑是中原地区的达官贵人墓葬的镇墓俑,是唐墓葬冥器中重要的一种神煞俑。为探究天王俑彩绘颜料的组成元素以及彩绘工艺,使用X射线荧光光谱分析了陕西省咸阳市渭城区苏同家族墓KTJ-2019-019M2、 KTJ-2019-019M3坑出土的天王俑彩绘区域的元素组成。分析结果表明陶俑表面金色贴片主要为金箔(Au);红色颜料的组成元素则是Hg、 S以及少量的Pb、 P;蓝色颜料和绿色颜料的组成元素均为Cu,白色颜料的组成元素为P、 S、 Pb。使用拉曼光谱对彩绘颜料层的鉴定物相,使用拉曼光谱分析技术对彩绘层分析结果确定了红色颜料的主要组成物相为朱砂(HgS)和铅丹(Pb₃O₄)的混合颜料;蓝色颜料的主要组成物相为石青;绿色颜料的主要组成物相为石绿;白色颜料的组成物相可能为铅白。进一步使用XRF面扫描技术分析了天王俑的彩绘工艺,解析金、红、蓝、绿色区域的组成元素位置,发现陶块样品中的M₂-1金色陶块、 M₃-1白色陶块、 M₃-2红色陶块、 M₃-3蓝色陶块、 M<...     

Origin of the discrepancy between photoluminescence brightness of TAG:Ce and electroluminescence brightness of TAG:Ce-based white LED expected from phosphor brightness

A yellow-emitting Tb(3)Al(5)O(12):Ce(3+) (TAG:Ce) phosphor was coated on blue light-emitting diodes (LEDs) to obtain white LEDs (WLEDs). Since TAG:Ce showed 90% of the brightness of Y(3)Al(5)O(12):Ce(3+) (YAG:Ce), it was expected that TAG:Ce-based WLEDs showed 90% of brightness of YAG:Ce-based ones. However, the TAG:Ce-based WLED showed 74% of the brightness of YAG:Ce-based one. Considering the density and size of the phosphors, the higher density and larger size of TAG:Ce induced a great deal of sedimentation of TAG:Ce particles in an epoxy resin. It is believed that this is one of main reasons for the reduced optical power of the TAG:Ce-based WLED compared to that of the WLED expected from the brightness of TAG:Ce.     

Electronic structure and luminescence characteristics of rare earth free self-activated Ca2Sb2O7 blue emitting phosphor

Over the past few years, extensive research has been focused on the development of rare-earth-free phosphors to achieve energy-efficient and cost-effective WLEDs with high luminous efficiencies for solid-state lighting applications. Herein, we report a novel rare-earth-free self-activated blue phosphor Ca₂Sb₂O₇, synthesized by solid-state reaction method. The electronic structure and bandgap of the material were determined by the density functional theory (DFT + U) method using Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. The prepared phosphor could be effectively excited in the range 280–370 nm resulting in a broad blue emission band, owing to the Sb⁵⁺ → O²⁻ transition in the (SbO₆)^7- group. The CIE chromaticity coordinates were found to be (0.144, 0.097) indicating intense blue emission with high color purity of 89%. Also, the prepared phosphor has good thermal stability and an internal quantum efficiency of 24%. All these results indicate that self-activated Ca₂Sb₂O₇ could be a potential blue phosphor for lighting and display devices.     

TiO2微粒对远程荧光粉膜及白光发光二极管器件光色性能的影响

利用热压法将TiO₂微粒掺入至YAG:Ce荧光粉和硅树脂中制备出远程荧光粉膜并封装成白光发光二极管(LED)器件, 通过荧光粉相对亮度仪、双积分球测试系统和可见光光谱分析系统对样品的光色性能及机理进行了研究. 结果表明: TiO₂的散射效应能够显著提高蓝光的利用率和黄光的透射强度, 白光LED器件的光通量在TiO₂浓度为0.966 g/cm³ 时达到最高值415.28 lm(@300 mA, 9.3 V), 提高了8.15%, 相关色温从冷白6900 K逐渐变化至暖白3832 K. TiO₂的掺入不仅提高了远程荧光粉膜的发射强度和白光LED器件的光通量, 同时能调控其相关色温.     

Improvement of electroluminescent property of blue LED coated with highly luminescent yellow-emitting phosphors

White light-emitting diodes (WLEDs) were fabricated by combining InGaN-based blue light-emitting diodes (LEDs) with highly luminescent Tb₃Al₅O₁₂:Ce³⁺ (TAG:Ce), Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce), and Sr₃SiO₅:Eu²⁺ (SS:Eu). The TAG:Ce-based WLED showed a color rendering index (R _a ) of 79 and a luminous efficiency (η _L ) of 34.1 lm/W at 20 mA. The YAG:Ce-based WLED and the SS:Eu-based WLED showed low R _a values of 75 and 57 but high luminous efficiency values of 38.9 and 41.3 lm/W at 20 mA, respectively. When a mixture of YAG:Ce and SS:Eu was coated on a blue LED and the resultant WLED operated at 20 mA, the WLED showed a highly bright white light similar to daylight (η _L =40.9 lm/W, color temperature T _c =5,716 K, and R _a =76). Moreover, the WLED showed stable color coordinates against a considerable variation of applied current.     

不同观察者锥细胞响应的同色异谱性能差异测试分析

为了研究不同年龄色觉正常观察者在不同观察条件下的锥细胞光谱响应差异,在CIELAB颜色空间选择了均匀分布的9个不同色调的颜色,组织27～35名观察者开展了两种不同光源照度和两种不同观察视场的四种观察条件下,基于显示色-打印色的颜色匹配实验。通过配色实验采集到不同观察者匹配颜色的光谱数据,与9个目标色的光谱数据计算、比较,以匹配的9个颜色最小平均CIEDE2000色差值出现的概率大小作为评价标准,检验CIE1931,CIE1964,CIE2006,Sarkar(S1～S8)共11种颜色匹配函数的表现,研究不同观察者锥细胞响应的同色异谱性。结果表明在四种不同实验条件下,表现最好的配色函数依次是CIE2006,S6,表现最差的是S1和S2。不同观察者的锥细胞响应同色异谱性差异较大,年龄因素对观察者的锥细胞响应的影响也较为明显。(λ)通道的光谱响应差异是造成不同观察者存在同色异谱现象的主要原因,大多数观察者的差异性主要集中在(λ)通道的峰值波长响应,峰值波长的位移对颜色匹配的结果影响不大。实验结果可为进一步划分不同观察者的颜色匹配函数,研究不同观察者的同色异谱性提供数据支持和理论依据。     

Sr9R2−xEuxW4O24 (R=Gd and Y) red phosphor for near-UV and blue InGaN-based white LEDs

Eu³⁺-activated phosphors, Sr₉R_2?xEu_xW₄O₂₄ (R=Gd and Y ), were prepared by the conventional solid-state reaction method and their photoluminescent properties were studied. The phosphors show intense red emission under 395 and 465 nm light excitation, which is matched with the light-emitting wavelength of a near-UV-emitting and a blue-emitting InGaN chips, respectively. Bright red-light-emitting diodes (LEDs) and white-light-emitting diodes (WLEDs) were fabricated by coating Sr₉Y _0.4Eu_1.6W₄O₂₄ phosphor onto ～395 nm-emitting InGaN chips and ～460 nm blue-emitting InGaN chips, respectively. The good performances of the LEDs demonstrate that the tungstates are suitable for application of near-UV and blue InGaN-based WLEDs.     

A potential red emitting K4Ca(PO4)2: Eu3+ phosphor for white light emitting diodes

Europium (III) ions doped red phosphors K₄Ca(PO₄)₂ were prepared first time by high temperature solid state reaction method. The prepared phosphors structure was examined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analyses. The thermal properties of the synthesized phosphor were investigated by differential scanning calorimetry (DSC) analysis. Photoluminescence (PL) spectra of K₄Ca(PO₄)₂:Eu³⁺ phosphors have shown strong red emission at 618 nm (⁵D₀→⁷F₂) with near UV an excitation wavelength of λ_exc=394 nm (⁷F₀→⁵L₆). In addition, the decay curves and CIE color coordinate measurements are also carried out. Hence, emission and excitation characterization of synthesized phosphors shows that the phosphors may be a promising red component for the application in the white light emitting diodes (WLEDs).     

基于Internet的远程电脑测配色系统

研发了一种基于Internet的远程电脑测配色系统。它能够实现远程测色和配色,具有多种配色模型,能够对来自不同行业的光谱数据以及光谱图像进行处理和分析。介绍了配色系统的部分设计。采用B/S和C/S相结合的构架实现了配色用户和配色服务商在互联网上的远程互动。介绍了有关的配色算法和远程配色系统的搭建过程以及相关程序编写方案。