We developed a procedure to prepare luminescent LiYF₄:Yb/LiYF₄ and LiYF₄:Yb,Er/LiYF₄ core/shell nanocrystals with a size of approximately 40 nm revealing luminescence decay times of the dopant ions that approach those of high-quality laser crystals of LiYF₄:Yb (Yb:YLF) and LiYF₄:Yb,Er (Yb,Er:YLF) with identical doping concentrations. As the luminescence decay times of Yb³⁺ and Er³⁺ are known to be very sensitive to the presence of quenchers, the long decay times of the core/shell nanocrystals indicate a very low number of defects in the core particles and at the core/shell interfaces. This improvement in the performance was achieved by introducing two important modifications in the commonly used oleic acid based synthesis. First, the shell was prepared via a newly developed method characterized by a very low nucleation rate for particles of pure LiYF₄ shell material. Second, anhydrous acetates were used as precursors and additional drying steps were applied to reduce the incorporation of OH⁻ in the crystal lattice, known to quench the emission of Yb³⁺ ions. Excitation power density (P)-dependent absolute measurements of the upconversion luminescence quantum yield (Φ_UC) of LiYF₄:Yb,Er/LiYF₄ core/shell particles reveal a maximum value of 1.25% at P of 180 Wcm⁻². Although lower than the values reported for NaYF₄:18%Yb,2%Er core/shell nanocrystals with comparable sizes, these Φ_UC values are the highest reported so far for LiYF₄:18%Yb,2%Er/LiYF₄ nanocrystals without additional dopants. Further improvements may nevertheless be possible by optimizing the dopant concentrations in the LiYF₄ nanocrystals.

我们开发了一种程序来制备发光LiYF ₄：Yb / LiYF ₄和LiYF ₄：Yb，Er / LiYF ₄核/壳纳米晶体，其尺寸约为40 nm，揭示出掺杂离子的发光衰减时间接近高质量的离子。具有相同掺杂浓度的LiYF ₄：Yb（Yb：YLF）和LiYF ₄：Yb，Er（Yb，Er：YLF）的激光晶体。随着Yb ³⁺和Er ³⁺的发光衰减时间已知对淬灭剂的存在非常敏感，核/壳纳米晶体的长衰变时间表明核颗粒中以及核/壳界面处的缺陷数量非常少。通过在常用的基于油酸的合成中引入两个重要的改进，可以实现性能的提高。首先，壳是通过新开发的方法制备的，其特征在于纯LiYF ₄壳材料颗粒的成核率非常低。第二，无水乙酸盐用作前体和附加的干燥步骤被用于减少OH的掺入^-在晶格中，已知以猝灭Yb组成的发射³⁺离子。励磁功率密度（P）该上转换发光量子产率（的依赖性绝对测量Φ _UC LiYF的）₄：镱，铒/ LiYF ₄芯/壳粒子在揭示的1.25％的最大值P 180 WCM的^-2。虽然比值下报道了NaYF ₄：18％的Yb，2％二核/壳纳米晶体具有相当的大小，这些Φ _UC值的最高迄今为LiYF报道₄：18％的Yb，2％ER / LiYF _4个纳米晶体没有额外的掺杂剂。尽管如此，通过优化LiYF ₄纳米晶体中的掺杂剂浓度，可能会有进一步的改进。