【作者】 宋秀峰；

【导师】 傅仁利；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2010， 博士

【摘要】 白光LED由于具有高效、节能、环保、绿色照明、长寿命等优点而受到人们广泛的关注,被预言将取代传统的照明光源-白炽灯、荧光灯等,成为第四代照明光源。目前技术上最成熟的白光LED的制备技术是荧光粉涂覆的光转换法。其中荧光粉对白光LED性能起着至关重要的作用。因此探求新型的可被紫外光或蓝光芯片激发的白光LED用荧光粉成为目前白光LED研究工作的热点硅基氮氧化物由SiX₄ （X = O,N）四面体形成的网络组成,具有很高的化学和热稳定性。富氮的晶体场环境引起较大的电子云重排效应（nephelauxetic effect）和能级劈裂使发光中心(Eu²⁺、Ce³⁺等)的5d能级重心降低。稀土离子掺杂的硅基氮氧化物荧光粉的激发带覆盖紫外光和蓝光区,正好与近紫外和蓝光LED芯片的发射光匹配。氮氧化物荧光粉可调制出蓝、绿、黄和红等各种不同波长的发射光谱,可满足白光LED的各种需求。硅基氮氧化物荧光粉因具有优良的荧光性能,被视为新型的制备白光LED理想的发光材料,吸引越来越多的人的关注。本文以氮氧化物MSi₂O₂N₂（M=Ca,Sr,Ba）为基质,研究稀土离子掺杂MSi₂O₂N₂（M=Ca,Sr,Ba）荧光粉的制备方法,光谱特性和光谱调控等内容,主要的研究工作如下几个方面:1.采用传统的固相反应法和以硅酸盐为先驱体的两步法制备MSi₂O₂N₂:Eu²⁺（M=Ca,Sr,Ba）荧光粉,研究制备工艺参数对MSi₂O₂N₂的物相组成和荧光性能的影响。固相反应合成的产物含有杂相且发光强度低。采用以硅酸盐为先驱体的两步法制备的样品杂相含量低,发光强度可提高1.5倍。2.系统地研究Eu²⁺或Ce³⁺离子掺杂的MSi₂O₂N₂（M=Ca,Sr,Ba）荧光性能。MSi₂O₂N₂:Eu²⁺ （M=Ca,Sr,Ba）的激发光谱覆盖250-500nm的紫外-可见光区,可与蓝光LED芯片匹配制备白光LED。发射光谱峰值分别位于560nm、535nm和490nm,是由Eu²⁺的4f65d→4f7跃迁造成的。MSi₂O₂N₂:Ce³⁺（M=Ca,Sr,Ba）激发光谱覆盖250-370nm的紫外光区,发射光谱峰值分别位于390nm、395nm和396nm。随着激活离子浓度的增加,发射光谱出现“红移”和浓度猝灭现象。3.研究共掺离子对MSi₂O₂N₂:Eu²⁺（M=Ca,Sr,Ba）的荧光性能的影响,共掺Mn²⁺,Ce³⁺和Dy³⁺可提高MSi₂O₂N₂:Eu²⁺（M=Ca,Sr,Ba）的发光强度。发现Ce³⁺-Eu²⁺之间存在能量传递,计算了Ce³⁺-Eu²⁺之间存在能量转换效率以及临界传输距离,发现Ce³⁺-Eu²⁺之间的能量传递的主要机制是电偶极-电偶极之间的相互作用。4.系统地研究了CaSi₂O₂N₂-SrSi₂O₂N₂-BaSi₂O₂N₂体系的互溶性以及Eu²⁺离子在基质中的发射光谱的可调性。CaSi₂O₂N₂与SrSi₂O₂N₂具有相同的晶体结构,可形成连续固溶体,Eu²⁺的发射光谱连续可调;SrSi₂O₂N₂与BaSi₂O₂N₂和CaSi₂O₂N₂与BaSi₂O₂N₂之间晶体结构各不相同,只能在某些成分范围内形成固溶体,Eu²⁺的发射光谱只能在某些范围内进行调制。更多还原

【Abstract】 White light-emitting diodes （LEDs） have drawn much attention owing to their excellent properties, such as high luminous efficiency, low power consumption, environment friendly, reliability, long life and so on. White LEDs show high potential for replacement of conventional lighting like incandescent and fluorescent lamps, and are considered as the fourth generation solid-state lighting. Today, commercial white LEDs are phosphor-converted-LEDs, which connect a blue LED chip and the phosphor. The phosphor plays an important role in white LEDs for improving the color rendering index and luminescence efficiency. So it is necessary to develop new phosphors for white LEDs.Silicon-based （oxy）nitrides are generally built up of networks of crosslinking Si（O,N）4 tetrahedra. The excited state of the 5d electrons of rare-earth elements is significantly lowered to low energy due to large crystal-field splitting and a strong nephelauxetic effect as a result of a high degree of crosslinking Si（O,N）4 tetrahedra in the structure of silicon-based （oxy）nitrides. This enables silicon-based （oxy）nitride to be excited efficiently by UV or blue-light irradiation. The structural versatility of （oxy）nitride phosphors makes it possible to attain all the emission colors of blue, green, yellow, and red; thus, they are suitable for using in white LEDs. This novel class of phosphors has been seemingly the most promising materials nowadays because of their high thermal and chemical stability and excellent photoluminescence properties. In present work, a systematic research was carried out on the processing methods, luminescence properties, spectral tuning of the rare earth doped MSi₂O₂N₂（M=Ca,Sr,Ba）. The main work contents and achievements can be summarized as the following:1, MSi₂O₂N₂:Eu²⁺（M=Ca,Sr,Ba） phosphors were prepared through a conventional solid state reaction method and a two step method with M2SiO4 as a precursor. The effect of formation processing on phase type and luminescence properties of samples was investigated. Low firing temperature leads to the sample including impurities and low luminescence intensity. Due to forming low content of the intermediate phase, the sample by the two step method shows luminescence intensity 1.5 times higher than that by the conventional method.2, Luminescence properties of Eu²⁺ or Ce3+ doped MSi₂O₂N₂（M=Ca,Sr,Ba） were systematically investigated. The excitation bands of MSi₂O₂N₂:Eu²⁺ （M=Ca,Sr,Ba） cover the spectral region from UV to the visible part（250-500nm）, the emission spectra show a single intense board emission band centered at 560nm,535nm and 490nm for M=Ca, Sr, Ba, respectively, which is ascribed to the allowed 4f65d→4f7 transitions of Eu²⁺. The excitation spectra of MSi₂O₂N₂:Ce3+（M=Ca,Sr,Ba） cover a broad band from 250 to 370nm. The emission bands of MSi₂O₂N₂:Ce³⁺ center at 390,395 and 396nm for M=Ca, Sr, Ba, respectively. With increasing the concentration of Eu²⁺or Ce³⁺, red-shift and concentration quenching of emission spectra were observed.3, The effect of co-activator (Mn²⁺, Ce³⁺, and Dy³⁺) on the luminescence behavior of Eu²⁺ activated MSi₂O₂N₂（M=Ca,Sr,Ba） phosphor was discussed in detail. The emission intensities of Eu²⁺ can be enhanced by co-doping with Mn²⁺, Ce³⁺, and Dy³⁺ in MSi₂O₂N₂（M=Ca,Sr,Ba）. There is an energy transfer between Ce³⁺ and Eu²⁺. The calculations of the efficiency of energy transfer from Ce³⁺ to Eu²⁺ and the critical distance between Ce³⁺ and Eu²⁺ suggest resonance-type energy transfer mechanism from Ce³⁺ to Eu²⁺ is due to dipole-dipole interactions.4, The intersolubility in the CaSi₂O₂N₂-SrSi₂O₂N₂-BaSi₂O₂N₂ system and the tenability of the emission of Eu²⁺ in these hosts were systematically investigated. Well solid solution can be formed throughout the whole composition range between CaSi₂O₂N₂ and SrSi₂O₂N₂, which have the same crystal structure, and therefore the emission of Eu²⁺ in these hosts can be continuously tuned. In the SrSi₂O₂N₂-BaSi₂O₂N₂ and CaSi₂O₂N₂-BaSi₂O₂N₂ system, solid solution can only be formed in some particular composition range due to different crystal structures. Therefore, the emission of Eu²⁺ in these hosts can only be tuned in composition ranges under which solid solution is formed.更多还原