Synthesis of novel Dy activated phosphate phosphors for NUV excited LED

The new trivalent dysprosium activated X₆AlP₅O₂₀ (where X=Sr, Ba, Ca and Mg) phosphors were prepared by the combustion method. The prepared phosphors are characterized by XRD, photoluminescence and SEM techniques. Excited by 350 nm near-ultraviolet (NUV) light, the phosphors show an efficient blue and yellow band emissions, which originates from the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ion, respectively. The excitation spectra of the phosphors are broadband extending from 340 to 400 nm, which are characteristics of NUV excited LED. The effect of the Dy³⁺ concentration on the luminescence properties of X₆AlP₅O₂₀:Dy³⁺ (where X=Sr, Ba, Ca and Mg) phosphors is studied. Ca₆AlP₅O₂₀ phosphors show strong PL emission intensity around 25 times more as compared to Ba₆AlP₅O₂₀, Sr₆AlP₅O₂₀ and Mg₆AlP₅O₂₀ phosphors. The investigated prepared phosphors are suitable for a NUV excited LED.     

Photoluminescence of (Ba1−xEux)Si6N8O (0.005≤x≤0.2) phosphors

Eu²⁺-doped BaSi₆N₈O phosphors (Ba_1−xEu_xSi₆N₈O, 0.005≤x≤0.2) were synthesized by gas-pressure sintering of the powder mixture of BaCO₃, Si₃N₄, and Eu₂O₃ at 1750 °C under 0.5 MPa N₂. The fired powder consists of a major BaSi₆N₈O phase and a trace amount of impurity phases. The structural result of the BaSi₆N₈O powder, refined by the Rietveld method, agrees well with that of single crystals. A wide blue luminescence band peaking at about 500 nm is observed in BaSi₆N₈O:Eu²⁺, upon excitation with the ultraviolet light of 310 nm. Although Eu is covalently bonded to six nearest neighbor nitrogen atoms, the luminescence of Eu²⁺ is not significantly redshifted but shows a very narrow excitation spectrum at high energies. The origin of the short-wavelength luminescence is mainly ascribed to a small crystal-field splitting as a result of extremely long distances between europium and nitrogen ligands in BaSi₆N₈O:Eu²⁺.     

Studies in crystal structure and luminescence properties of Eu-doped metal tungstate phosphors for white LEDs

The correlation between the crystal structure and luminescent properties of Eu³⁺-doped metal tungstate phosphors for white LEDs was investigated. Red-emitting A_4−3x(WO₄)₂:Eu_x³⁺ (A=Li, Na, K) and B_(4−3x)/2(WO₄)₂:Eu_x³⁺ (B=Mg, Ca, Sr) phosphors were synthesized by solid-state reactions. The findings confirmed that these phosphors exhibited a strong absorption in the near UV to green range, due to the intra-configurational 4f-4f electron transition of Eu³⁺ ions. The high doping concentration of Eu³⁺ enhanced the absorption of near UV light and red emission without any detectable concentration quenching. Based on the results of a Rietveld refinement, it was attributed to the unique crystal structure. In the crystal structure of the Eu³⁺-doped metal tungstate phosphor, the critical energy transfer distance is larger than 5 Å so that exchange interactions between Eu³⁺ ions would occur with difficulty, even at a high doping concentration. The energy transfer between Eu³⁺ ions, which causes a decrease in red emission with increasing concentration of Eu³⁺, appears to be due to electric multi-polar interactions. In addition, the Eu-O distance in the host lattice affected the shape of emission spectrum by splitting of emission peak at the ⁵D₀→⁷F₂ transition of Eu³⁺.     

Synthesis and luminescence of Eu-doped alkaline-earth apatites for application in white LED

A series of Eu²⁺-doped alkaline-earth apatites (alkaline-earth=Ca, Sr and Ba) were synthesized by a solid state reaction method with excess chlorides, and the effect of the used excess chlorides on the luminescent property of the synthesized products was discussed. Photoluminescence measurements showed that Eu²⁺-doped calcium apatite exhibited intensely blue wide-band emission peaking at 457 nm under near UV excitation among the Eu²⁺-doped Ca, Sr and Ba apatites. Blue and white LEDs were successfully fabricated by pre-coating the calcium apatite phosphors onto ∼395 nm-emitting InGaN chips. The CIE coordinates, color temperature, luminous efficacy and rendering index value of the fabricated white LED are (0.3432, 0.3234), 4969 K, 8 lm/W and 80, respectively. The results indicate that the Eu²⁺-activated calcium apatite phosphor is a promising candidate as a blue component for fabrication of near UV-based white LEDs.     

蓝色荧光粉Sr2B5O9Cl:Eu2+发光特性的研究

采用高温固相法合成了近紫外光激发的蓝色荧光粉Sr₂B₅O₉Cl:Eu²⁺,研究了SrCl₂ ·6H₂O用量和Eu²⁺浓度对其结构和发光性能的影响.随着Eu²⁺浓度的增加,其结构无明显变化,发光强度先增强后减弱,当其浓度为8mol%时,荧光粉的发光强度最大;当用Ca取代Sr时,荧光粉的发射峰从425 nm红移到453 nm. 适当过量 关键词： 氯硼酸盐 蓝色荧光粉 LED     

白光LED用硅氮基荧光粉材料研究进展

随着白光LED技术的迅速发展,传统YAG∶Ce3+荧光粉由于低显色性、高色温等因素制约而难以满足发展需求。利用近紫外芯片激发三基色荧光粉成为获得白光LED的一种有效途径,因而发展高性能三基色荧光粉具有重要意义,尤其红光发光材料更是当务之急。硅氮基化合物包含由SiN₄四面体构成的网络结构,具有很高的化学稳定性和热稳定性。该类荧光粉因其结构的多样性,且在紫外-蓝光区具有高的吸收效率,因而随着基质和激活离子的改变,发射光谱可覆盖整个可见光区域,并具有较高的光转换效率和光色稳定性,对温度和驱动电流的变化不敏感等优点,因而此类研究对白光LED的发展具有深远的影响。综述了近年来硅氮基荧光粉制备方法及研究的最新进展,系统地归纳总结了硅氮基荧光粉的晶体结构及发光性能等特性,并分析了目前国际上对该材料的研究动态及应用情况。     

Solid-solution red phosphors for white LEDs

Solid solutions of Eu³⁺-doped metal tungstate and molybdate phosphors were synthesized by solid-state reactions. The crystal structure of the solid-solution phosphors was determined to be tetragonal with a space group of I4₁/c. The red-emitting solid-solution phosphors exhibited a broad absorption band in the range 220-340 nm and sharp excitation peaks in the near UV to green region. The emission intensities of the solid-solution phosphors were enhanced due to the stiff lattices, as a result of the ordered distribution of cations and anions according to differences in ionic size. The increase in the energy transfer is discussed in terms of metal-ligand distances, ionization potential of Mo and the relatively large overlap between the excitation and emission spectra. Such solid-solution phosphors with a bright red emission intensity, relatively short decay time and appropriate color chromaticity have potential for use as red-emitting materials for white LEDs.     

白光LED用Ca3Si3O9：Dy3+荧光粉的制备及其发光性能

采用溶胶-凝胶法制备了可用于白光LED的新型Ca₃Si₃O₉:Dy³⁺荧光粉, 通过对样品的X 射线衍射谱及光致发光光谱的测试和表征, 研究了Ca₃Si₃O₉:Dy³⁺的物相结构和发光性能. 结果显示, Ca₃Si₃O₉:Dy³⁺的发射光谱是由位于483 nm和577 nm处的主峰构成的双峰谱线, 激发光谱为多峰宽谱, 谱峰位于290–480 nm范围内. Dy³⁺掺杂浓度对Ca₃Si₃O₉:Dy³⁺发光性能有明显的影响, 随着Dy³⁺浓度的增大, Ca₃Si₃O₉:Dy³⁺的发光强度和黄、蓝光发射强度比 (Y/B) 均呈现先增大后减小的规律, 最大发光强度值对应的Dy³⁺浓度为1 mol%. 电荷补偿剂Li⁺能提高Ca₃Si₃O₉:Dy³⁺的发光强度, 特别当Li⁺浓度为2–4 mol%时, 荧光粉的蓝光发射强度显著增大. 关键词： 白光LED 溶胶-凝胶法 3Si₃O₉：Dy³⁺')" href="#">Ca₃Si₃O₉：Dy³⁺ 发光特性     

Ca1−xMo1−ySiyO4:Eux: A novel red phosphor for white light emitting diodes

Single phase of Ca_1−xMo_1−ySi_yO₄:Eu_x³⁺ (0.18?x?0.26, 0?y?0.04) was synthesized by solid-state method. The photoluminescence investigation indicated that Ca_1−xMoO₄:Eu_x³⁺ (0.18?x?0.26) could be effectively excited by 393 and 464 nm, and it exhibited an intense red emission at 615 nm. The introduction of Si⁴⁺ ions did not change the position of the peaks but strongly enhanced the emission intensity of Eu³⁺ under 393 and 464 nm excitations and showed very good color purity. The emission intensity of optimal Ca_0.8Mo_0.98Si_0.02O₄:Eu_0.2³⁺ sample (excited by 393 nm) was about 5.5 times higher than that of the phosphor Y₂O₂S:0.05Eu³⁺. So this phosphor could be nicely suitable for the application of the UV LED chips.     

一种基于RGB三基色LED的白光光源

数字光源处理(DLP)投影技术是投影显示的一个重要分支,基于发光二极管(LED)照明技术的DLP投影显示技术则是目前DLP技术的一个重要发展方向。根据DLP投影显示技术的需要,对一种新型的LED混光光源进行了优化设计和仿真计算,得到了一种适合于为DLP微型投影机提供照明的LED混光光源。该混光光源可以提高LED光源的DLP微型投影机的光通量。     

远程荧光体白光发光二极管的发光性能

研究了高色温和低色温两种球冠状远程荧光粉白光LED在不同电流、不同热沉温度下的发光性能差异.结果表明:在大电流下,LED有源层内由于量子限制斯塔克效应使其峰值波长向短波方向移动,偏离了高色温荧光粉的最佳激发波长,更加接近低色温荧光粉的最佳激发波长.高色温LED的相关色温随电流增加呈上升趋势,低色温LED的相关色温随电流增加呈下降趋势,与它们的量子效率变化引起的色坐标漂移有很大关系.两种LED量子效率和发光效能随热沉温度的升高均呈略微增大的趋势;其中,高色温LED的量子效率和发光效能随电流的增大而减小,而低色温LED的量子效率和发光效能则随电流的增大而升高;高色温LED发光性质较低色温LED好,但色特性的稳定程度不如低色温LED.     

白光LED远程荧光粉技术研究进展与展望

远程荧光粉技术通过将荧光粉与芯片分离,降低了荧光粉的工作环境温度,提升了荧光粉的稳定性,改善了白光LED的照明品质和光效,同时有望降低LED眩晕度,提供大面积平板光源,在未来照明与显示应用中具有重要意义。远程荧光粉技术的白光LED将向多功能化、高性能化和智能化方向发展。本文将综述白光LED远程荧光粉技术的研究进展,主要介绍其封装工艺的优化、评价参数的构建和分析,以及相关荧光材料的发展现状。     

A survey of phosphors novel for thermography

With regard to phosphor thermometry, seven luminescent ceramic materials were synthesised and characterised, namely CaMoO₄:Eu³⁺, CaTiO₃:Pr³⁺, LaPO₄:Eu³⁺, LaVO₄:Eu³⁺, LiAl₅O₈:Fe³⁺, TiMg₂O₄:Mn⁴⁺ and ZnGa₂O₄:Mn²⁺. In this context, emission spectra and temperature lifetime characteristics are presented. Thus, a survey of phosphors novel for thermography is given in order to encourage further studies and more detailed characterisations of the respective materials.     

一种新的用于直下式LCD背光源的LED

传统的薄膜晶体管液晶显示器作为一种被动发光器件,本身不会发光,必须依靠背光源提供照明。在背光照明用到的光源中,LED最具竞争力。在分析LED性能的基础上,设计了一种用于大尺寸直下式背光源的LED,新设计的LED结构简单,性能优良。通过设计26英寸背光源验证了新的LED。模拟结果表明,新的LED可以满足大尺寸LCD背光源对亮度均匀性和颜色均匀性的要求。     

大功率LED筒灯散热封装设计与分析

设计了一种大功率白光LED照明灯具的封装结构,通过有限元计算,分析其稳态工作下的温度场分布,并通过温度测试实验表明,器件上测试点温度76.0℃,散热器外壳温度71.0℃,误差分别为2.6%和2.3%,理论计算与实验结果基本吻合。在此基础上,结合灯具各构件的温度场分布与传热学原理,提出了一种新的散热封装结构,为大功率LED的散热优化方案提供了有效依据。     

Optimization of a GaN-based irregular multiple quantum well structure for a dichromatic white LED

GaN-based irregular multiple quantum well(IMQW) structures assembled two different types of QWs emitting complementary wavelengths for dichromatic white light-emitting diodes(LEDs) are optimized in order to obtain near white light emissions.The hole distributions and spontaneous emission spectra of the IMQW structures are analysed in detail by fully considering the effects of strain,well-coupling,valence band-mixing and polarization effect through employing a newly developed theoretical model from the k · p theory.Several structure parameters such as well material component,well width,layout of the wells and the thickness of barrier between different types of QWs are employed to analyse how these parameters together with the polarization effect influence the electronic and the optical properties of IMQW structure.Numerical results show that uniform hole distributions in different types of QWs are obtained when the number of the QWs emitting blue light is two,the number of the QWs emitting yellow light is one and the barrier between different types of QWs is 8nm in thickness.The near white light emission is realized using GaN-based IMQW structure with appropriate design parameters and injection level.     

Preparation and luminescent properties of (Ca1-x,Srx)S:Eu red-emitting phosphor for white LED

The (Ca_1−x,Sr_x)S:Eu²⁺ red-emitting phosphors were prepared by using sulfide and sulfate in CO-reductive atmosphere, respectively, and their luminescent properties have been investigated. The XRD data showed that the doping of divalent Europium ion (Eu²⁺) enlarges the lattice parameters, and Sr/Ca ratio not only affects the lattice parameters, but also influences the emission peak. The excitation and emission spectra indicated that this phosphor can be effectively excited by visible light from 430 to 500 nm, and exhibits a satisfactory red performance. The annealing treatment process was also discussed in detail. Compared with the commercial afterglow sulfide phosphor, the present synthesized phosphor has higher emission efficiency and is a favorable choice for white light-emitting diode (LED). The white LED implanted by present phosphor shows desirable luminescence and chromaticity properties.     

荧光粉比例对白光LED特性的影响

用黄色和橙色硅酸盐荧光粉制备了白光LED,调整黄粉和橙粉的比例得到不同的色温.对样品进行光学测试,发现黄粉与橙粉的比例小于7时,黄光部分的峰值约590 nm,比例大于7时,黄光部分的峰值约570 nm;显色指数和流明效率都是随色温的增大先上升后下降,5521 K时达到最优值,这是由于低色温时,荧光粉的浓度大导致不能有效...     

基于空封技术的白光数码管寿命的研究

在实验数据的基础上,分析了空封白光数码管光通量性能低于传统白光数码管的原因,提出了有针对性地提高光通量的一些初步设想.对空封白光数码管进行了温度老化实验,老化温度分别为80℃和100℃.在80℃老化实验中,700h时的光通量随时间缓慢降低,但到700多小时后在某个时刻突然急剧降低.通过对实验数据的分析,解释了空封白光数...     

一种基于视觉评价的白光LED显色指数改进算法

现行的CIE显色指数对白光LED的评价结果存在与视觉感知不符的问题,需要新的显色指数计算方法或对CIE显色指数进行改进。提出了一种基于视觉实验改进的计算白光LED显色指数的新方法。通过色块样本的光谱反射比与光源相对光谱功率分布之间的关系,改进了显色指数计算公式,得到改进后的显色指数。把CIE显色指数与改进后的显色指数分别与视觉评价结果进行对比,证实了改进后的显色指数更符合视觉评价结果。