多元体系超大尺寸稀土层状化合物单层纳米片的高效剥离与功能化

Two dimensional nanophosphors of high quality play an important role in the miniaturization and intelligentization of opto-electronic components. This project focuses on the synthesis of ultra-large single crystals of Y/(Gd,Tb)/Eu complex layered rare earth hydroxide (LRH) via controlled processing, the efficient exfoliation of LRH single crystals into ultra-large unilamellar nanosheets, and the functionalization of the nanosheets via the constrcution of oriented fluorescent films of novel structural features. Ultra-large (＞30μm) LRH single crystals will be obtained by hydrothermal synthesis, which are then efficiently delaminated into unilamellar nanosheets with a lateral size of ＞10μm and a thickness of ~1nm via hydrothermal anion exchange, intercalation, and inter-layer expansion. Highly stable transparent suspensions containing the ultra-large nanosheets will also be prepared. "Rare-earth oxide/silica-sphere array" complex fluorescent films with a high [111] orientation, a rare-earth oxide layer thickness of ＜100nm, and a spherically curved surface will be constructed with the ultra-large nanosheets and silica monospheres as building blocks. Luminescent properties of the films will be optimized by taking advantages of the [111] crystallographic orientation, the spherically curved surface, and the efficient energy transfer from Gd3+(Tb3+) to Eu3+. Photoluminescent performances of the films are expected to be modulated by the photonic crystal structure, and the underlying mechanism will also be clarified. Highly fluorescent films of excellent transparency, which show luminescence stronger than both the surface-smooth films and the powder form, will be finally obtained. This project may provide new concepts for the design of efficient phosphors and luminescent films.

二维纳米荧光材料的高品质化对光电元器件微型化、智能化的发展至关重要。本项目针对Y/(Gd,Tb)/Eu多元体系超大尺寸稀土层状化合物（LRH）单晶颗粒的可控合成、超大尺寸LRH单层纳米片的高效剥离与功能化展开系统研究。采用水热法合成出Y/(Gd,Tb)/Eu多元体系超大尺寸（＞30μm）LRH单晶颗粒，通过水热离子交换、插层柱撑高效剥离出边长尺寸＞10μm、厚度~1nm的LRH单层纳米片，并获得稳定分散于介质中的纳米片溶胶。以超大尺寸纳米片为构筑单元制备出具有高度[111]取向、稀土氧化物层厚度＜100nm、表面呈球形曲面状的"稀土氧化物/二氧化硅球阵列"复合透明荧光膜。利用结晶取向、球形曲面与"Gd3+(Tb3+)→Eu3+"的有效能量传递优化荧光性能，利用光子晶体结构调制荧光发射、明确作用机制，获得荧光性能优于表面平整取向膜与相应粉体的高品质透明荧光膜，为荧光材料提供新的设计思路。

以NH4NO3作为矿化剂，利用高温水热首次合成出边长尺寸50-300微米（通常5微米以下）的Y/Eu二元系和Y/Tb/Eu、Y/Gd/Eu、Y/Gd/Dy多元体系超大尺寸稀土层状化合物（LRH）单晶颗粒，并明确了结晶机制。发现提高水热温度和添加矿化剂NH4NO3促进LRH晶粒长大。采用水热离子交换实现了LRH层间硝酸根与含长碳链的十二烷基磺酸根（DS-）和油酸根（oleate）大尺寸有机阴离子的完全置换，并将柱撑产物分散于甲酰胺和甲苯中，高效剥离出边长尺寸达60微米（一般500nm以下）、厚度2nm以下的单晶LRH纳米片，并获得稳定分散于介质中的纳米片溶胶。基于水热离子交换的动力学过程，首次提出了大尺寸LRH有机阴离子交换的蠕动模式。以超大尺寸纳米片为构筑单元制备出具有高度[111]取向、厚度100nm左右的Y/Eu二元系和Y/Tb/Eu、Y/Gd/Eu、Y/Gd/Dy多元体系致密稀土氧化物，发现了“Gd3+(Tb3+)→Eu3+(Dy3+)”的能量传递、并分析传递效率和机理。利用结晶取向和“Gd3+(Tb3+)→Eu3+(Dy3+)”的有效能量传递显著提高了荧光膜的发光强度。以二氧化硅球阵列为模板、以大尺寸纳米片为构筑单元成功制备出表面呈球形曲面状的复合透明荧光膜，利用球形曲面进一步增强了荧光强度。利用不同稀土离子的共掺杂实现了荧光膜的调色功能。

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