基于能量传递改善氟硅酸盐荧光粉热稳定性的发光动力学机理

Searching for phosphors with high thermal stability under the near UV excitation is the key to further broaden the applications of white LEDs. In view of the existing problems of the thermal stability, and based on our previous findings, the goal of this project is intended to improve the thermal stability of the fluosilicate phosphors with apatite-structure to satisfy the requirements of different white LEDs by utilizing the energy transfer in Ce3+-Tb3+ system, and then forming solid solutions via ionic substitution to further optimize the local surroundings of the activators, the energy difference between the lowest 5d level of Ce3+ and the 5D4 level of Tb3+ as well as regulate the distribution of the activators. Using the spectral technology and luminescent dynamics, we will systematically analyze the change tendency of the thermal stability of the phosphors with the compositions of the solid solutions, the lowest 5d level of Ce3+ as well as the distribution of the activators, and then establish a reasonable energy transfer rate equation to elucidate the luminescent dynamics mechanism underlying the improved thermal stability due to energy transfer. Our results will provide theoretical guidance for designing and synthesizing novel rare earth ion doped luminescent materials with high thermal stability under the near UV excitation.

探索适于近紫外激发且热稳定性优异的荧光粉是进一步拓宽白光LED应用领域的关键。本项目针对荧光粉的热稳定性问题，在前期工作的基础上，选取具有磷灰石结构的氟硅酸盐为基础材料，利用Ce3+-Tb3+体系的能量传递实现材料热稳定性的提高。通过离子取代形成固溶体的方式，优化Ce3+的局域晶格环境,调节Ce3+5d能级与Tb3+5D4能级的相对位置，调控激活离子的格位分布，从而获得满足白光LED器件需求的荧光粉。利用光谱技术手段和发光动力学原理，重点分析荧光粉的热稳定性随固溶体组分、Ce3+5d能级高度、激活离子格位分布的变化规律，并建立合理的能量传递速率方程，阐明基于能量传递提高热稳定性的发光动力学机理。本项目的研究成果对于开发和设计适于近紫外激发且热稳定性优异的新型白光LED用荧光粉具有指导意义。

发光材料的热稳定性是评价其是否能真正应用于LED领域的关键参数之一。本项目围绕研究计划内容与预期目标，利用离子取代形成固溶体的方式对氟硅酸盐基质进行改造，实现了对材料激发峰位的调控及热稳定性的提高，并成功制备了适于近紫外激发且发光性能优异的白光LED用荧光粉。研究了材料的组分、结构、激活离子的格位分布与发光性能的关系，揭示了Ce3+-Tb3+体系内的能量传递过程提高材料热稳定性的物理机理。取得的成果包括：（1）采用高温固相法，合成了Ba2Gd3(SiO4)3F: Ce3+, Tb3+、Sr2La3(SiO4)3Cl: Ce3+, Tb3+、Ca3Gd2Si6O18:Ce3+, Tb3+等发光材料，实现对掺杂离子局域晶格环境的调控，并利用光谱手段研究研究材料的发光性能，明确了Ce3+-Tb3+体系内存在的能量传递过程提高材料热稳定性的相关机理。（2）采用高温固相法合成了具有石榴石结构的Ca2LaZr2Ga2.8Al0.2O12: Cr3+, Yb3+、Gd3Al2Ga3O12: Cr3+及具有类钙钛矿结构的Mg4Ta2O9:Cr3+宽带近红外荧光粉，研究了Cr3+-Yb3+体系内与Ce3+-Tb3+体系相似的能量快传递过程对材料热稳定性的影响。本项目的研究成果为基于固溶体理论及能量传递机理的无机发光材料的研发、材料热稳定性的改善及相关发光机理的研究提供实验和理论基础。