利用非等价取代调控优化荧光材料的发光性能

发布时间：2019-02-25 18:55

【摘要】：近年来,随着不可再生能源的不断消耗,能源危机已经成为举世瞩目的焦点。白光LED照明技术以其效率高、寿命长的特点逐渐成为照明显示领域的主流,为缓解能源危机做出了重要的贡献。因此,用于白光LED的荧光粉也越来越成为科研工作者研究的热点,包括传统的硅酸盐、铝酸盐荧光粉。本论文主要研究了 KMg_4(P0_4)_3:Ce~(3+),Tb~(3+)和 Ca_~(2+)xLa_(8-x)(Si0_4)_60~(2-)x:Eu~(2+)两种绿色荧光粉的晶体结构和发光性能,并考察了其在白光LED领域的应用价值。重点是非等价取代对荧光粉发光性能的影响。本论文分为四章:第一章为绪论,介绍了人类照明发展的历史、白光LED技术、荧光粉的发光机理以及常用荧光粉。根据上述原理提出了本论文的实验思路。第二章介绍了 KMg_4(P04)_3:Ce~(3+),Tb~(3+)荧光粉的制备和能量传递机理。同时,作为一个非等价取代的例子,本章深入地导论了 Ce~(3+)、Tb~(3+)在KMg_4(PO_4)_3晶格中的占据位。通过对KMg_4(PO_4)_3的晶体结构进行细致深入的分析,又结合XRD和EPR的测试结果,证明了 Ce~(3+)、Tb~(3+)均取代K~+的位置,同时为了平衡非等价取代时多余的正电荷,会有O~(2-)进入到KMg_4(P04)_3晶格的管道中。实验还发现Ce~(3+)可以很大程度上提高Tb~(3+)的发光强度。激发光谱、发射光谱以及荧光寿命曲线都证明了 Ce~(3+)和Tb~(3+)之间能量传递的存在。计算结果显示在该荧光粉中能量传递的效率高达95%以上。通过理论分析,发现能量传递的机理是偶极-四极相互作用。第三章介绍了 Ca_~(2+)xLa_(8-x)(Si0_4)_6O_(2-0.5x):yEu~(2+)荧光粉的相关研究成果,包括合成方法、晶体结构、发光性质及其晶格中Eu~(3+)离子的还原机理。我们通过增加晶体中Ca_~(2+)离子的比例、减少La~(3+)离子的比例,成功使Eu~(3+)还原为Eu~(2+),从而大大增强荧光粉的绿光发射,峰值位于510nm。我们认为由于Ca_~(2+)取代La~(3+)是不等价取代,使晶格中的O~(2-)离子数减少,从而降低Eu~(3+)被还原的难度。XANES测试结果表明随着x值增大,荧光粉中Eu~(2+)离子的数目确实增多了。Rietveld精修结果显示所得Ca_~(2+)xLa_(8-x)(Si0_4)_6O_(2-0.5x)(x=0、1、2)晶体均属于六方晶系,空间群为P6/3m(176),且随着x值增大,晶体中氧离子的量减少。EPR数据也证明了 Ca_~(2+)离子取代La~(3+)离子后,晶体中氧空位增多。这些结果都证明了我们提出的Eu~(3+)的还原机理。另外,我们还以Ca6La4(SiO_4)_6:0.04Eu~(2+)作为绿粉,配合365nm近紫外LED芯片和商用的蓝粉、红粉,成功地制得了显色性良好的白光LED灯,这表明Ca_6La_4(SiO_4)_6:0.04Eu~(2+)绿色荧光粉具有商用于白光LED领域的应用潜力。第四章对论文做出了总结,指出了研究工作中不足的地方,为进一步的研究提出了一些可行的意见。
[Abstract]:In recent years, with the constant consumption of non-renewable energy, energy crisis has become the focus of worldwide attention. White LED lighting technology has become the mainstream of lighting display field because of its high efficiency and long life. It has made an important contribution to alleviate the energy crisis. Therefore, the phosphor used in white LED is becoming more and more popular, including traditional silicate and aluminate phosphor. In this thesis, the crystal structure and luminescence properties of two kinds of green phosphors (KMg_4 (P0 / 4) _ 3, Tb~ (3) and Ca_~ (2) xLa_ (8) (Si0_4) _ (602 -) ~ (2 -) ~ (2 -) EU ~ (2) have been studied. The value of its application in the field of white light LED was also investigated. The effect of non-equivalent substitution on the luminescent properties of phosphors was studied. This paper is divided into four chapters: the first chapter is the introduction, introduces the history of human lighting development, white LED technology, phosphor luminescence mechanism and common phosphors. According to the above-mentioned principles, the experimental ideas of this paper are put forward. In chapter 2, the preparation and energy transfer mechanism of KMg_4 (P04) _ 3 and Tb~ (3) phosphors are introduced. At the same time, as an example of non-equivalent substitution, this chapter gives an in-depth introduction to the occupation of Ce~ (3) and Tb~ (3) in KMg_4 (PO_4) _ 3 lattices. By analyzing the crystal structure of KMg_4 (PO_4) _ 3 in detail and combining with the test results of XRD and EPR, it is proved that Ce~ (3) and Tb~ (3) replace the position of K ~, and that Ce~ (3) and Tb~ (3) take the place of K ~. At the same time, in order to balance the excess positive charge when the substitution is not equivalent, O2-will enter into the pipe of KMg_4 (P04) 3 lattice. It is also found that Ce~ (3) can greatly improve the luminescence intensity of Tb~ (3). Excitation spectra, emission spectra and fluorescence lifetime curves all prove the existence of energy transfer between Ce~ (3) and Tb~ (3). The calculated results show that the efficiency of energy transfer in the phosphor is over 95%. Through theoretical analysis, it is found that the mechanism of energy transfer is dipole-quadrupole interaction. In chapter 3, the related research results of Ca_~ (2) xLa_ (8 x) (Si0_4) _ 6O _ (2): yEu~ (2) phosphor are introduced, including the synthesis method, crystal structure, and so on. Luminescence properties and reduction mechanism of Eu~ (3) ion in lattice. By increasing the ratio of Ca_~ (2) ions in crystals and decreasing the proportion of La~ (3) ions, we have successfully reduced Eu~ (3) to Eu~ (2), thus greatly enhancing the green emission of phosphors with a peak value of 510 nm. We think that the substitution of Ca_~ (2) for La~ (3) is not equivalent, which reduces the number of O2-ions in the lattice, thus reducing the difficulty of reducing Eu~ (3). The XANES test results show that with the increase of x value, the number of O2-ions in the lattice decreases. The number of Eu~ (2) ions in phosphor did increase. Rietveld refined results showed that Ca_~ (2) xLa_ (8) (Si0_4) _ 6O _ (2) (x, 0. 5x) (x 0, 1, 2) crystals all belong to hexagonal system. The amount of oxygen ions in the crystals decreases with the increase of x value. It is also proved by EPR data that the oxygen vacancies in the crystals increase with the substitution of Ca_~ (2) ions for La~ (3) ions. All these results prove the reduction mechanism of Eu~ (3) proposed by us. In addition, we also used Ca6La4 (SiO_4) 6? 0.04 EU2 as green powder, combined with 365nm near ultraviolet LED chip and commercial blue powder and red powder, and successfully prepared white LED lamp with good chromaticity. The results show that Ca_6La_4 (SiO_4) 6? 0.04 EU2 green phosphor has the potential of commercial application in the field of white LED. The fourth chapter summarizes the paper, points out the deficiencies in the research work, and puts forward some feasible suggestions for further research.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ422

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