“全掺杂”多级核壳上转换发光材料的构筑与发光调控机理研究

Rare earth doped upconversion luminescent materials have show great applications in the fields of lighting display, bioimaging, medical diagnosis and treatment. However, the optimum doping concentration of luminescent center is generally less than 3 mol%, which limits the luminescent efficiency to a low level. Based on this problem, this project mainly focuses on the controllable synthesis and luminescent properties of "fully doped" multistage core-shell upconversion luminescent materials. By epitaxy coating different active shell layers on the surface of upconversion particles, the surface quenching effect can be suppressed, and the "fully doped" of the rare earth ions is realized. In addition, the infrared light absorption rate can be improved by sensitization between different rare earth ions, thereby improving the luminescent efficiency. At the same time, the controllable preparation of "fully doped" upconversion particles with multistage core-shell, yolk and hollow structure is studied by introducing SiO2 inert core and combined with chemical etching method. The luminescence efficiency is further improved by changing the spatial structure. Finally, the crystal model is constructed by quantum chemical calculation method, and the fluorescence quenching mechanism and the luminescence efficiency enhancement mechanism of upconversion particles with different shell and cavity structures is systematically studied. The relationship between the microstructure and luminescence properties is studied in detail, which provides an important theoretical basis and scientific experimental basis for the development of new high-efficiency upconversion luminescent materials.

稀土掺杂上转换发光材料在照明显示、生物成像和医学诊断与治疗等领域展现着巨大的应用前景。但目前已报道的上转换材料中，发光中心的最佳掺杂浓度普遍低于3mol%，导致上转换发光效率一直被限制在较低水平。基于该问题，本项目拟以“全掺杂”多级核壳上转换发光材料的可控制备与发光性能研究为主，通过在上转换粒子表面外延包覆不同组成的活性壳层，一方面抑制表面猝灭效应实现稀土离子“全掺杂”，另一方面利用敏化作用提高红外光吸收率，进而提高发光效率。同时，通过引入SiO2惰性核并结合化学刻蚀法，可控制备多级核壳、蛋黄和中空结构“全掺杂”上转换粒子，利用空间结构的改变调控入射光的利用率进一步提高发光效率。最后，利用量子化学计算方法构建晶体模型，系统研究不同壳层组成和腔体结构上转换粒子的荧光猝灭抑制机理和发光效率增强机制，揭示微观结构与发光性能的构-效关系，为开发新型高效上转换发光材料提供重要理论基础和科学实验依据。

稀土掺杂上转换发光材料在照明显示、生物成像和医学诊断与治疗等领域具有巨大的应用前景，但是浓度猝灭效应导致的发光效率偏低仍是制约其广泛实际应用的关键科学问题。因此，本项目以NaErF4为内核构筑了一系列“全掺杂”核壳上转换发光体系（NaErF4@NaYF4，NaErF4@SiO2，NaErF4@NaYF4:Yb3+），系统探究了惰性和活性外延壳层晶体结构、组成、厚度对上转换发光性能的影响规律。研究表明，外延壳层可以有效阻断内核发光中心到表面猝灭位点的能量损失路径，抑制表面荧光猝灭效应，提高上转换发光性能。同时，通过引入敏化剂等改变壳层组成和晶体结构可以增强激发光的吸收并调节发射光的颜色。另外，通过引入SiO2惰性内核，成功构筑了一系列SiO2@Gd2O3:Yb3+,Ln3+(Ln=Er, Tm, Ho)和SiO2@Gd2O3:RE3+(RE=Tb, Dy, Eu)核壳微球发光体系，与体相材料相比，核壳微球由于有效降低了入射光的散射并改善了结构缺陷，展现了更优异的发光性能。同时，通过改变壳层中稀土离子的种类和掺杂浓度，利用不同稀土离子间的能量传递行为有效增强了发光强度并实现了多色发光。最后，通过深入分析并对比不同核壳发光材料中的能量传递路径和激发光利用率，明晰了表面猝灭抑制机理、能量传递机理和发光增强机制，揭示了微观结构与发光性能的构-效关系。此外，本项目还开展了荧光探针在真实水体和生物体中金属离子等组分检测的应用研究，展现了优异的灵敏度和选择性。上述研究结果表明构筑全掺杂核壳材料是提高发光性能一个有效策略，为新型高效上转换发光材料的开发和应用提供了重要理论基础和科学实验依据。