【作者】 姚山山；

【导师】 严有为；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2011， 博士

【摘要】 白光发光二极管(White Light Emitting Diode,简称WLED)是继白炽灯、荧光灯和高压气体放电灯之后的第四代光源。由于具有节能、高效、绿色环保和寿命长等优点,WLED代表了未来照明产业的发展方向,得到了世界各国特别是发达国家的重点关注和加速研发。从WLED实现技术来看,单芯片LED搭配无机发光材料(即荧光粉)的组合方式相对于多芯片直接组合方式具有显色性好、设计简单及成本低等优势,是目前固态照明技术发展的主流。因此,开展新型、稳定、高效LED荧光粉的研制,对于WLED技术的发展具有重要的意义。硅酸盐荧光粉是近年来发展起来的一类能够较好满足WLED要求的新型无机发光材料。但是,硅酸盐荧光粉的基质成分、晶体结构、电子能带结构、激活剂匹配以及制备工艺与发光性能之间的关系等目前尚无系统深入的研究,而且该类荧光粉目前均采用高温固相法合成,存在能耗大、成本高、合成产物纯度低、颗粒粒径分布不均等不足。为此,本文采用溶液燃烧合成(Solution Combustion Synthesis,简称SCS)技术合成WLED硅酸盐荧光粉,并研究合成材料的晶体结构、基质电子能带结构及发光性能。通过系统研究,取得如下主要成果。采用SCS技术制备了Ba2MgSi2O7:Eu2+蓝绿色荧光粉。产物纯净,结晶完好,颗粒分布均匀。该荧光粉的激发光谱为宽激发带,能被紫外(Ultraviolet, UV)LED芯片有效激发。在353 nm的UV光激发下样品的发射峰波长为498 nm,归属于Eu2+的4f65d1→4f7(8S7/2)宽带允许跃迁,色度坐标(x,y)=(0.14,0.41)。研究了Ba1.95(Mg1-y, Zny)Si2O7:Eu0.052+系列荧光粉的发光性能。结果表明,Zn2+的掺杂明显提高了Ba2MgSi2O7:Eu2+在UV光区域的发光性能；随着y值的增加,导致基质的晶体场增强和电子云膨胀效应的发生,致使Eu2+发射主峰红移5 nm。采用正交实验法研究了Ba2ZnSi2O7:Eu2+荧光粉的发光特性。研究结果表明,在1000℃煅烧3 h,助熔剂H3BO3的加入量为0.06 mol,激活剂Eu2+为0.05 mol时,所制备的荧光粉发光性能最佳。激活剂Eu2+在荧光粉基质中浓度猝灭为0.05 mol,浓度猝灭机理为电子偶极-电子偶极相互作用。该荧光粉能被UV-LED有效激发,色度坐标为(x,y)=(0.16,0.45)。为了与SCS法进行对比分析,采用优选原料,通过Sol-gel法在还原气氛下制备了Ba2ZnSi2O7:Eu2+荧光粉。制备产物的发射峰与SCS相比,其发射峰蓝移3 nm,归因于发光离子受纳米尺寸效应使得晶体内部键之间震动频率升高,引起发射峰“蓝移”。同时,以NaOH为矿化剂,通过水热一步法制备了Eu掺杂Ba2ZnSi2O7荧光粉。结果表明,样品中Eu仍以Eu3+存在,荧光光谱与Eu3+光谱特征完全相符。其发射光谱主峰位于614 nm,属于晶格中占据非对称中心格位Eu3+的5D0→7F2的电偶极跃迁特征线性发射。经还原处理后,样品中Eu3+被全部还原成Eu2+,发射波长位于501 nm,归属于Eu2+的4f65d1→4f7宽带允许跃迁。SCS法与Sol-gel法,水热法制备的Ba2ZnSi2O7:Eu2+荧光粉经光谱测试表明,SCS法制备Ba2ZnSi2O7:Eu2+荧光粉发光性能更优,激发峰和发射峰强度都高于Sol-gel法和水热法。研究了基质阳离子Ba/Zn比值对硅酸盐荧光粉的晶体结构和发光性能的影响。采用溶液燃烧合成法制备了Ba/Zn比值分别为1：2和1：1的BaZn2Si2O7: Eu2+和BaZnSiO4: Eu2+荧光粉。结果表明,在BaZn2Si2O7:Eu2+荧光粉发射峰单一位于522 nm,呈Gaussian对称分布。但是在BaZnSiO4:Eu2+出现了403 nm和505 nm的发射峰。对505 nm发射峰进行Gaussian曲线拟合,得到了492和512 nm两个明显的发射峰。其中403,492和512 nm发射峰分别为Eu2+占据六配位(Ba(3))和九配位(Ba(2)和Ba(1))的Ba2+格位跃迁产生的。为了更好的理解Eu2+掺杂黄长石结构A2DSi2O7(A=Ba, Sr, Ca; D=Mg, Zn)的发光性质,分别对Ba2MgSi2O7、Ba2ZnSi2O7、Sr2ZnSi2O7、Ca2ZnSi2O7的硅酸盐基质晶体的电子能带结构进行了基于第一性原理的密度泛函理论的模拟计算。结果表明,黄长石结构硅酸盐晶体的价带顶主要由02p轨道组成,同时过渡金属元素轨道Zn3d轨道有显著贡献；其导带底则主要出Si的(3s+3p)轨道和基质晶体结构中的碱土金属元素轨道如Ca3d、Sr4d和Ba5d轨道构成。因此当稀土激活剂离子Eu2+占据黄长石晶体结构中碱土金属离子的晶格晶位时,由于其基质晶体能带结构不同,引起其发光特性不同。采用SCS法制备了新型硅钙钡石型BaCa2Si309:Eu2+蓝色荧光粉。结果表明,该荧光粉的激发波长是由260 nm-450 nm的宽激发带组成,能被UV-LED有效激发。在356nmUV光激发下,发射峰位于445 nm,归属于Eu2+的4f65d1→4f7跃迁,色度坐标为(x,y)=(0.16,0.11)。研究了系列锌黄长石结构M2ZnSi207:Eu3+(M=Ca, Sr, Ba)红色荧光粉的发光性能。结果表明,三种荧光粉的激发和发射光谱峰形状和位置基本没有改变。三种荧光粉的激发光谱中都存在320,362,383,394,416和465 nm的激发峰,分别对应于Eu3+的7F0→3H4,7F0→5D4,7F1→5F4,7F0→5L6,7F1→5L6和7F0→5D2的电子跃迁。发射光谱中都存在579,591,614,652,703nm的发射峰,分别对应于Eu3+的5D0→7Fo,5D0→7F1,5D0→7F2,5D0→7F3,5D0→7F4的跃迁。同时也证明了Eu3+的f-f跃迁基本不随基质的不同而改变。由于单斜晶系Ba2ZnSi207的晶体对称性在系列锌黄长石结构中最低,Eu3+占据Ba2+的晶格晶位时,5D0→7F2(电偶极跃迁)与5D0→7F1(磁偶极跃迁)的比值最大。合成的三种荧光粉都可以被395 nm UV和465 nm蓝光有效激发,发射614 nm的红光。激发波长与UV-LED和Blue LED芯片发光相符合,是潜在的WLED用红色荧光粉。更多还原

【Abstract】 White light emitting diode (WLED) is believed to be the fourth generation of lamp-house after incandescent lamp, fluorescent lamp and discharge light and there are the futures of illumination. WLED represents the future direction of development of the lighting industry due to its attravive advantages of energy consumption saving, high-efficiency, environmental and lifetime long-lasting aspects, which has been focus of attention and speed up research and development in around the world especially developed countries. From the realization point of view with WLED technology, the single-chip LED with inorganic luminescent materials (phosphors) of the combination relative of the multi-chip direct combination with good color, simple design and low cost advantages, which is the mainstream development of solid-state lighting. Therefore, it is a great significance to make novel, stable and efficient development of LED phosphors for WLED technology.Silicate phosphor is a class developed in recent years to meet the requirements of the new WLED inorganic luminescent materials. However, there is no systematic study the current matrix of silicate phosphor composition, crystal structure, electronic band structure, activating agent and synthesis method matching between luminescent properties. The solid-state reaction process has been used intensively for silicates phosphors, but this approach is the need for high-temperature and long-time calcinations. The unreacted phases appeared easily which reduced greatly its luminescent brightness and intensities characteristic. In the present works, the silicates phosphors synthesized by the solution combustion synthesis (SCS) method and researched the crystal structure, electronic structures and luminescence properties of synthetic materials. The main results obtained are as follows.The Ba2MgSi2O7:Eu2+ blue-green phosphors were synthesized by combustion synthesis method and its luminescent properties were also investigated. The results of XRD and SEM analysis show the sample is nonophasic and well-crystallized. The excitation wavelength of these phosphors can be effectively excited by UV-LED chip. The emission wavelength lies at 498 nm upon excited by 353 nm UV light. The Commission International de l’Eclairage (CIE) of the optimized sample was calculated (x, y)=(0.14, 0.41).The luminescent properties of Ba1.95(Mg1-y, Zny)Si2O7:Eu0.052+ phosphors were researched. The results shown that the introduction of Zn2+ into Ba2MgSi2O7:Eu2+ effectively increased its emission with UV excitation. In addition, the emission spectra presented an emission position red shift of up to 5 nm with increasing y value, which due to the crystal field enhancing and electron cloud expansion effect.The hardystonite phosphor Ba2ZnSi2O7:Eu2+ researched by the orthogonal design method. The results shown that the postannealed temperature at 1000℃for 3 h, the quantity of flux H3BO3 was 0.06 mol and the activator ions of Eu2+ was 0.05 mol could get the optimized phosphors. The critical quenching concentration of Eu2+ in Ba2ZnSi2O7: Eu2+ phosphor is about 0.05. The corresponding concentration quenching mechanism is verified to be a dipole-dipole interaction. The excitation wavelength of these phosphors can be effectively excited by UV-LED chip. The CIE of the Ba1.95ZnSi2O7:Eu0.052+was calculated (x, y)=(0.16,0.45).The Ba2ZnSi2O7:Eu2+ phosphors have also been prepared by a modified Sol-gel method in the reducing atmosphere. A blue-green emission with a peak at 500 nm is observed, which show the Eu2+ typical emission. Compared with the products of combustion synthesis, its emission peak blue-shift 3 nm, mainly due to activators in nano-size effect makes the vibration frequency between the bonds internal the crystal increases. At the same time, NaOH used as mineralizer to prepare Ba2ZnSi2O7:Eu phosphors by hydrothermal method. The results indicate that, the sample emission prominent peak locates at 614 nm, being attribute to 5Do→7F2 electric-dipole transitions of Eu3+ ions lie in non-centrosysmetrical sites. After the sample is reduced in the reducing atmosphere, a blue-green emission with a peak at 501 nm is observed, which shows the Eu3+ ions has been completely reduced to Eu2+ Comparison analysis of the Ba2ZnSi2O7: Eu2+ phosphor fabricated by SCS method, Sol-gel method and hydrothermal method respectively indicates that the phosphors can be excited by UV irradiation. However, the combustion method to prepare Ba2ZnSi2O7:Eu2+ phosphor powders have more uniform leading to the better performance. The luminescent intensity is higher than the Sol-gel and hydrothermal method. The process of combustion synthesis method is simple and more energy-saving.Morever, the crystal structure and luminescent property of silicates phosphors are considerable influenced by Ba/Zn ratio. The green-emitting phosphors of the BaZn2Si2O7: Eu2+ and BaZnSiO4:Eu2+ was prepared by SCS method. The emission of BaZn2Si2O7: Eu2+ phosphor showed one Gaussian symmetric peak at 522 nm. But in the structure of BaZnSiO4:Eu2+ phosphor, Eu2+ ions occupy three different lattice sites by substitution for Ba2+. Eu2+ions on Ba(1) and Ba(2) sites gave emissions at about 512 nm and 492 nm, while Eu2+ ions on Ba(3) sites showed an emission band at 403 nm.To further understand the photoluminescence properties of the melilites phosphors, the electronic band structures calculation were performed on Ba2MgSi2O7, Ba2ZnSi2O7, Sr2ZnSi2O7 and Ca2ZnSi2O7 by the first principle of density functional theory. The calculated results shown that the valence band top of these melilites silicate crystals was mainly composed of the O2p orbitals, also the transition-metal-element orbitals such as Zn3d orbitals contributed significantly to the valence band top and contracted the band gap. The low conduction band contained the Si3s and Si3p orbitals, also included the alkaline-metallic element orbitals such as the Ca3d, Sr4d and Ba5d orbitals. So, the rare earth activator Eu2+ ions occupy the alkaline earth metal ions in the melilite crystal structure, the host crystal band structure caused the different luminescence characteristics.A blue emitting phosphor BaCa2Si3O9:Eu2+ was prepared by the combustion synthesis method. The excitation spectrum is a broad extending from 260 to 450 nm, which matches the emission of UV-LED. The emission spectrum shows a single intensive band centered at 445 nm, which corresponds to the 4f65d1→4f7 transition of Eu2+. The CIE of the sample was calculated (x, y)= (0.16,0.11).Luminescent properties of hardystonite M2ZnSi2O7: Eu3+ (M=Ca, Sr, Ba) red phosphors have been systematically studied. The results showed that the excitation and emission spectra of phosphors did not change the shape and positions. The excitation peaks of these phosphors about 320, 362,383,394, 416 and 465 nm are assigned to correspond to 7F0→3H4,7F0→5D4,7F1→5F4,7F0→5L6,7F1→5L6 and 7F0←5D2 transitions of Eu3+, respectively. The spectrum exhibits five emission peaks at 579,591,614,652 and 703nm. These five emission peaks can be attributed to the 5D0→7F0,5D0→7F1,5D0→7F2, 5D0→7F3,5D0→7F4 transitions of Eu3+. These results show that the f-f transitions of Eu3+ basically dose not change with the different hosts. When the activator of Eu3+ codoped Ba2+, the ratio of the 5D0→7F2 (electric dipole transition) and 5D0→7F1 (magnetic dipole transition) is maximum. The experiment results show that the monoclinic Ba2ZnSi2O7 have the lowest crystal symmetry in the melilite structure. These phosphors have main excitation peaks located at 394 and 465 nm, which match the emission of UV and blue-LED, respectively. Thus, these luminescent materials could be used as red phosphors for WLED.更多还原