【作者】 李勇；

【导师】 尹民； 张慰萍；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2009， 博士

【摘要】 本论文由三章组成,第一章介绍了稀土发光材料的研究背景;第二章是关于稀土离子掺杂(Ce³⁺,Tb³⁺,Eu³⁺)的Ln₂Si₂O₇（Ln=Lu,Gd,Y）的制备和发光性质研究;第三章是关于稀土离子掺杂的GdOCl材料的制备和上转换发光的研究。第一章首先给出稀土发光材料的研究热点,然后着重讨论了发光的基本原理和三价稀土离子的发光特性,并介绍了制备发光材料的几种方法。在论文的第二章中,首先介绍了稀土硅酸盐发光材料的研究进展;然后详细讨论了Ce³⁺,Tb³⁺,Eu³⁺掺杂的Lu₂Si₂O₇、Y₂Si₂O₇、Gd₂Si₂O₇的制备、表征和发光性质。利用溶胶凝胶法制备稀土离子(Ce³⁺,Tb³⁺,Eu³⁺)掺杂的Lu₂Si₂O₇、Y₂Si₂O₇、Gd₂Si₂O₇纳米粉末,然后用多种手段表征了Ln₂Si₂O₇的物相和结构,对样品的合成温度和掺杂离子的浓度对结构的影响也进行了研究。结果表明,在1100℃合成温度下,Lu₂Si₂O₇成β相,在1000℃合成温度下成α相。而且掺杂浓度对合成产物的结构也有影响,Lu₂Si₂O₇的β相在掺杂浓度较高时转变成了α相。但是类似的掺杂离子的浓度影响产物结构的现象并没有在Y₂Si₂O₇、Gd₂Si₂O₇粉末的制备中看到。1000℃合成温度下,Y₂Si₂O₇、Gd₂Si₂O₇均成α相。稀土离子(Ce³⁺,Tb³⁺,Eu³⁺)掺杂的Lu₂Si₂O₇、Y₂Si₂O₇、Gd₂Si₂O₇纳米粉末在室温下的激发和发射谱利用同步辐射光源的设备测得。光谱分析表明:Ce³⁺,Tb³⁺离子掺杂的各种基质样品的激发谱均观察到了基质吸收,各自的4f-5d跃迁吸收带。掺Eu³⁺的样品中除了有基质吸收还观察到4f-4f组态内跃迁吸收和电荷迁移态Eu³⁺.O^2-吸收。还进行了Gd₂Si₂O₇:Eu³⁺发光动力学研究,发现衰减时间随着Eu³⁺浓度的增大而缩短,随样品合成温度的上升而增大。Ce³⁺到Tb³⁺的能量传递在Ce³⁺,Tb³⁺双掺的各种基质样品中存在。在Ce³⁺,Tb³⁺双掺的Gd₂Si₂O₇基质样品中除了Ce³⁺到Tb³⁺的能量传递之外还观察到了Gd³⁺→Tb³⁺,Gd³⁺→Ce³⁺和Tb³⁺→Ce³⁺的能量传递。Tb³⁺→Ce³⁺的能量传递是通过Gd³⁺离子来进行的。第三章研究了各种稀土离子掺杂的GdOCl粉末的上转换发光,首先介绍了上转换发光的应用,研究历史和研究进展,然后讨论了各种上转换发光基质和发光离子,讨论了上转换发光的影响因素。利用固相法制备了稀土离子掺杂的GdOCl粉末,用X-射线衍射,扫描电镜和拉曼光谱对其结构和形貌进行了表征。结果表明,粉末呈片状,粒径大约为1um,厚度约为250nm。拉曼光谱分析表明GdOCl基质的声子截止频率小于510cm^-1。研究了Er³⁺掺杂的GdOCl粉末在980nm和514.5nm激发下的上转换光谱。在980nm激发下,观察到绿色和红色上转换可见光。上转换发光峰的强度随激发功率的关系表明上转换过程是双光子过程。另外观察到了红绿光强度的比值随掺杂浓度的增加而增大的现象。在514.5nm激发下,在GdOCl:Er样品中观察到了蓝色上转换,通过对上转换发光的激发光功率和Er³⁺离子浓度的依赖关系的研究,分析了具体的上转换发光机制。激发态吸收和能量传递是可能的上转换机制。Yb³⁺的掺杂能增强GdOCl:Er³⁺的上转换的发光强度,而且观察到红光绿光强度的比值随Yb³⁺掺杂浓度的升高而增加的现象,分析了具体的上转换发光机制。另外观察到了在980nm激发下的Tm³⁺-Yb³⁺,Ho³⁺-Yb³⁺,Tb³⁺-Yb³⁺,Pr³⁺-Yb³⁺的各种上转换发光,并分析了其中的上转换机制。更多还原

【Abstract】 This dissertation consists of three chapters. Chapter 1 introduces the background of rare earth luminescent materials. Chapter 2 deals with the preparation, characterization and luminescent properties of Ln₂Si₂O₇ （Ln=Lu,Gd,Y,） powders doped with rare earth ions (Ce³⁺,Tb³⁺,Eu³⁺). And upconversion in rare earth ions doped GdOCl powders is presented in Chapter 3.In chapter 1, an introduction of rare earth luminescent materials is given at first. Then the basic principles of luminescence and properties of rare-earth ions are stated. At last, several preparation methods of rare earth doped luminescent compounds are presented.In chapter 2, the recent research progress of rare earth doped silicate were given, then preparation, characterization and luminescent properties of the rare earth ions (Ce³⁺,Tb³⁺,Eu³⁺) doped in Lu₂Si₂O₇、Y₂Si₂O₇、Gd₂Si₂O₇ samples are presentedThe rare earth ions (Ce³⁺,Tb³⁺,Eu³⁺) doped in Lu₂Si₂O₇、Y₂Si₂O₇、Gd₂Si₂O₇ nanocrystals were prepared by sol-gel method. And their structural properties were studied by X-ray diffraction （XRD）, and thermal-gravimetry analysis and differential thermal analysis （TG-DTA）. The effects of different concentrations and synthetic temperature on the structure of the nanopowders were studied. According to the XRD patterns, the lutetium pyrosilicate （Lu₂Si₂O₇） crystallized in the two structural types depend on synthetic temperature and doping concentration. The samples sintered at 1100°C with low doping concentration crystallized in typicalβ-Lu₂Si₂O₇ structure with partcle size about 40nm, while the samples sintered at 1100°C with high concentration or sintered at 1000°C crystallized inα-Lu₂Si₂O₇ structure. Gd₂Si₂O₇ and Y₂Si₂O₇ sintered at 1000°C crystallized in a structure, and the doping concentration had no effects in structure. The excitation and emission spectra of Ln₂Si₂O₇ （Ln=Lu,Gd,Y,） powders doped with rare earth ions (Ce³⁺,Tb³⁺,Eu³⁺) at room temperature by using synchrotron radiation as the excitation source. The typical components of Ce³⁺, Tb³⁺ and Eu³⁺ excitation and emission spectra appear. The host absorption and the f-d transition bands all exist in the excitation spectra of Ce³⁺ and/or Tb³⁺ doped samples. And the excitation spectra of Eu³⁺ doped samples consist of the host absorption, charge transfer band of Eu³⁺-O^2- and the f-f transition bands. The fluorescence decay times of Gd₂Si₂O₇:Eu³⁺ were analyzed. A distinct decreasing of lifetime with increasing Eu³⁺ contents was observed, and the luminescence lifetimes of samples increased with increasing synthesis temperatures.The energy transfer from Ce³⁺ to Tb³⁺ were all observed in Ce³⁺ and Tb³⁺ co-doped samples. The reverse energy transfer phenomenon of Tb³⁺ to Ce³⁺ via Gd³⁺ sublattice in Gd₂Si_O7 sample was also observed. There were another energy transfer such as Gd³⁺→Tb³⁺, Gd³⁺→Ce³⁺ in Ce³⁺,Tb³⁺ co-doped Gd₂Si₂O₇ system.In chapter 3, the upconversion in rare earth ions doped GdOCl powders were investigated. An introduction about upconversion phenomenon, its application, history and research progress were given firstly, and then chosen of matix, doping ions and the influence of upconversion efficiency were discussed.The rare earth doped GdOCl powders were prepared by solid state reaction. The structural properties of GdOCl powders were studied by XRD, scanning electron microscope （SEM） and Raman spectroscopy. XRD and SEM show that the samples sintered at 1000°C crystallized in typical GdOCl structure with particle size about 1um. Raman spectra show that the phonon cutoff of GdOCl is smaller than 510cm^-1.The upconversion luminescence properties of Er³⁺ doped GdOCl powders with exicitation of 980nm and 514.5nm were investigated, respectively. Under 980nm laser excitation, green and red upconversion were observed in GdOCl:Er samples. Laser power dependence on upconverted emissions confirmed that two-photon absorption upconversion process was involved for the green and red upconversion emissions. The effect of doping concentrations was also discussed. The enhancement of the ratio of red intensity to green intensity with the increasing of Er³⁺ was observed and analyzed. Under 514.5nm laser excitation, blue upconversion was observed in GdOCl:Er³⁺ samples. Laser power and doping concentration dependence of the upconversion were studied to understand the upconversion mechanisms. Excited state absorption and energy-transfer processes are the possible mechanisms of the visible emissions.Yb³⁺ codoping enhanced the upconversion emission intensities of Er³⁺ doped GdOCl powders. The enhancement of the ratio of red intensity to green intensity with the increasing of Yb³⁺ was observed and upconversion mechanisms were analyzed. The upconversion of Tm³⁺-Yb³⁺, Ho³⁺-Yb³⁺, Tb³⁺-Yb³⁺, Pr³⁺-Yb³⁺ co-doped GdOCl powders under 980nm excitation were also observed, and their upconversion mechanisms were also analyzed, respectively.更多还原