Abstract A variety of α-NaYF4@YOF composites with diverse morphologies and particles sizes have been fabricated via an easy-to-operate approach. First of all, the YB(OH)4CO3 precursor was obtained by a urea-based homogeneous precipitation route. Subsequently, the uniform and well-dispersed β-NaYF4 microcrystals with a variety of crystal shapes were synthesized by a simple hydrothermal process. The morphology and particle size of the β-NaYF4 samples can be adjusted in a controlled manner by simply tuning the reaction temperature and time, feeding molar ratio of precursor/NaF, or total amount of the reactants. Finally, the β-NaYF4 microcrystals converted to α-NaYF4@YOF composites which inherited the morphology and dispersity of the hydrothermal products after an annealing process in air. Upon UV or NIR excitation, the as-synthesized lanthanide ions Ln3+ (Eu3+, Tb3+, Yb3+/Er3+, Yb3+/Ho3+) doped α-NaYF4@YOF samples show the intense characteristic down-conversion (DC) or up-conversion (UC) multicolor emissions. Moreover, the calcination process not only broadens the excitation range but also improves the emission efficiency of the phosphors due to the enhanced crystallintiy and formation of YOF shell. The as-synthesized Ln3+-doped luminescent materials may find potential applications in fields of color displays, optoelectronic devices, and light-emitting diodes (LEDs).

中文翻译：

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多形貌NaYF4@YOF复合微晶的可控合成及发光性能

摘要 通过易于操作的方法制备了多种具有不同形态和粒径的 α-NaYF4@YOF 复合材料。首先，YB(OH)4CO3 前驱体是通过尿素基均相沉淀路线获得的。随后，通过简单的水热法合成了具有多种晶形的均匀且分散良好的β-NaYF4微晶。β-NaYF4 样品的形态和粒径可以通过简单地调整反应温度和时间、前体/NaF 的进料摩尔比或反应物的总量以可控的方式进行调整。最后，β-NaYF4微晶转化为α-NaYF4@YOF复合材料，其在空气中退火后继承了水热产物的形态和分散性。在紫外或近红外激发下，合成的镧系元素离子 Ln3+ (Eu3+, Tb3+, Yb3+/Er3+, Yb3+/Ho3+) 掺杂的 α-NaYF4@YOF 样品显示出强烈的特征下转换 (DC) 或上转换 (UC) 多色发射。此外，煅烧过程不仅拓宽了激发范围，而且由于增强的结晶度和 YOF 壳的形成而提高了荧光粉的发射效率。合成的 Ln3+ 掺杂发光材料可能在彩色显示器、光电器件和发光二极管 (LED) 领域有潜在的应用。煅烧过程不仅拓宽了激发范围，而且由于增强的结晶度和 YOF 壳的形成而提高了荧光粉的发射效率。合成的 Ln3+ 掺杂发光材料可能在彩色显示器、光电器件和发光二极管 (LED) 领域有潜在的应用。煅烧过程不仅拓宽了激发范围，而且由于增强的结晶度和 YOF 壳的形成而提高了荧光粉的发射效率。合成的 Ln3+ 掺杂发光材料可能在彩色显示器、光电器件和发光二极管 (LED) 领域有潜在的应用。