The spatial distribution and concentration of lanthanide activator and sensitizer dopant ions are of key importance for the luminescence color and efficiency of upconverting nanoparticles (UCNPs). Quantifying dopant ion distributions and intermixing, and correlating them with synthesis methods require suitable analytical techniques. Here, X-ray photoelectron spectroscopy depth-profiling with tender X-rays (2000–6000 eV), providing probe depths ideally matched to UCNP sizes, is used to measure the depth-dependent concentration ratios of Er³⁺ to Yb³⁺, [Er³⁺]/[Yb³⁺], in three types of UCNPs prepared using different reagents and synthesis methods. This is combined with data simulations and inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurements of the lanthanide ion concentrations to construct models of the UCNPs’ dopant ion distributions. The UCNP sizes and architectures are chosen to demonstrate the potential of this approach. Core-only UCNPs synthesized with XCl₃·6H₂O precursors (β-phase) exhibit a homogeneous distribution of lanthanide ions, but a slightly surface-enhanced [Er³⁺]/[Yb³⁺] is observed for UCNPs prepared with trifluroacetate precursors (α-phase). Examination of Yb-core@Er-shell UCNPs reveals a co-doped, intermixed region between the single-doped core and shell. The impact of these different dopant ion distributions on the UCNP's optical properties is discussed to highlight their importance for UCNP functionality and the design of efficient UCNPs.

中文翻译：

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NaYF4:Yb3+、Er3+ 上转换纳米粒子中的活化剂和敏化剂离子分布的量化通过深度剖析与温柔的 X 射线光电发射

镧系元素活化剂和敏化剂掺杂离子的空间分布和浓度对于上转换纳米粒子 (UCNPs) 的发光颜色和效率至关重要。量化掺杂剂离子分布和混合，并将它们与合成方法相关联需要合适的分析技术。在这里，X 射线光电子能谱深度剖析与柔和的 X 射线 (2000–6000 eV)，提供与 UCNP 尺寸理想匹配的探针深度，用于测量 Er ³⁺与 Yb ³⁺的深度相关浓度比， [尔³⁺ ]/[Yb ³⁺]，在使用不同试剂和合成方法制备的三种类型的 UCNPs 中。这与数据模拟和镧系元素离子浓度的电感耦合等离子体发射光谱 (ICP-OES) 测量相结合，以构建 UCNP 掺杂剂离子分布的模型。选择 UCNP 大小和架构是为了展示这种方法的潜力。用 XCl ₃ ·6H ₂ O 前体（β 相）合成的纯核 UCNPs 表现出镧系元素离子的均匀分布，但表面略微增强的 [Er ³⁺ ]/[Yb ³⁺] 观察到用三氟乙酸前体（α 相）制备的 UCNP。Yb-core@Er-shell UCNPs 的检查揭示了单掺杂核和壳之间的共掺杂、混合区域。讨论了这些不同掺杂剂离子分布对 UCNP 光学特性的影响，以突出它们对 UCNP 功能和高效 UCNP 设计的重要性。