Synthesis and Luminescence Properties of Rare Earth Fluorides and Metal Tungstate Nano-/Micromaterials

在现代化学和材料科学中，纳米/微米材料的尺寸和形貌控制引起了学术界的广泛关注，如何合理控制材料的定向生长，调节其组成、形貌、尺寸以及维度，进而更好的理解晶体生长的复杂现象、揭示其潜在的基本理论和原理并最终实现按照人们的设计合成功能材料具有十分重要的意义。本论文在稀土氟化物和钨酸盐纳米/微米材料的设计合成、形貌控制、形成机制以及发光性质等方面进行了一些探索性的研究。 发展了一种简单、整体、没有模板、环境友好的水热方法合成系列稀土氟化物。用有机添加剂柠檬酸钠(Na3C6H5O7•2H2O)作为配位剂和形貌控制剂，通过改变氟源(NaF, NH4F或NaBF4)和最初溶液的pH值，得到了具有不同成分、晶体结构、尺寸和形貌的稀土氟化物，包括二元氟化物LnF3 (Ln = La-Lu)和三元氟化物NaREF4 (RE = Y, Yb, Lu)；首次研究了具有各种晶体结构和形貌的含镱(Yb)和镥(Lu)的二元和三元氟化物的可控合成；对各种产物可能的形成机理进行了合理、系统的讨论；并对各种基质中Eu3+, Tb3+掺杂的下转换和Yb3+/Er3+, Yb3+/Ym3+共掺杂的上转换发光性质进行了详细的研究。由于具有优良的荧光性质和可控的形貌和尺寸，这些发光材料可能在光显示、光发射二级管(LEDs)、固体激光器等领域有着潜在的应用价值。这些研究结论不仅丰富了稀土氟化物化学的内容，而且探索了纳米/微米材料的晶体生长规律和形成机理。 采用超声化学途径合成了CaWO4, CaWO4:Eu3+和CaWO4:Tb3+亚微米尺寸的球形荧光粒子，详细讨论了合成材料的结构、形成机理、光致发光、阴极射线发光性质以及能量传递现象，为其它钨酸盐的合成提供了新的思路。In modern chemistry and materials science, the precisely architectural manipulation of nano- and microcrystals with well-defined morphologies and accurately tunable sizes has drawn extensively attention. One of the challenging and urgent task in this area is how to rationally control the orientation growth of materials and manipulate their compositions, morphologies, sizes as well as dimensionality, consequently achieving a better understanding of the observed complex phenomena of crystal growth, revealing the underlying fundamental theories and principles and realizing the design of functional materials. In this dissertation, valuable explorations have been carried out on the new synthetic strategies to rare earth fluorides and metal tungstate nano-/micromaterials as well as controlled morphologies, formation mechanisms and luminescence properties. The main contents can be summarized as follows: A facile, general, template-free and environmentally friendly hydrothermal methodology has been developed to prepare the whole rare earth fluorides nano- and microcrystals. Organic additive trisodium citrate plays double roles of coordination ligand and shape modifier in determining the morphologies of the final products. Through the precise tuning several critical parameters including F- sources (NaF, NH4F, NaBF4), pH value in the initial solution and the choice of organic additives, the rare earth fluorides with various compositions, crystal structures, uniform sizes and morphologies have been obtained easily, including binary fluorides LnF3 (Ln = La-Lu), and ternary NaREF4 (RE = Y, Yb, Lu). More importantly, for the first time, the controllable synthesis of ytterbium (or lutetium) fluoride compounds with diverse crystal phase and morphologies have been reported. The possible formation mechanisms for products with various architectures have been presented systematically. The photoluminescence properties of Eu3+, Tb3+-doped DC and Yb3+/Er3+, Yb3+/Ym3+ -codoped UC NaREF4 or REF3 have also been investigated in detail. Due to their unique luminescence properties and controlled morphology and size, these phosphors may find potential applications in the fields of color displays, light-emitting diodes (LEDs), and solid-state lasers. These results not only enrich the contents of lanthanide fluorides chemistry but also provide fundamental insights into the crystal growth and formation mechanism of nano/microscale materials. A facile and effective sonochemical method has been illustrated to fabricate CaWO4, CaWO4:Eu3+and CaWO4:Tb3+ submicron spherical phosphor particles. The structure, formation mechanism, and luminescence properties for as-prepared samples were investigated in detail. This novel and efficient pathway could open new opportunities for further investigating the novel properties of tungstate materials