BAM Federal Institute for Materials Research and Testing, Division 1.10 Biophotonics, Richard-Willstaetter-Str. 11, 12489 Berlin, Germany.
Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, 93040 Regensburg, Germany.
Nanoscale. 2017 Mar 23;9(12):4283-4294. doi: 10.1039/c7nr00092h.
The rational design of brighter upconversion nanoparticles (UCNPs) requires a better understanding of the radiationless deactivation pathways in these materials. Here, we demonstrate the potential of excitation power density (P)-dependent studies of upconversion (UC) luminescence intensities, slope factors, and absolute quantum yields (Φ) of popular β-NaYF:20% Yb,2% Er UCNPs of different surface chemistries in organic solvents, DO, and water as a tool to gain deeper insight into the UC mechanism including population and deactivation pathways particularly of the red emission. Our measurements, covering a P regime of three orders of magnitude, reveal a strong difference of the P-dependence of the ratio of the green and red luminescence bands (I) in water and organic solvents and P-dependent population pathways of the different emissive energy levels of Er. In summary, we provide experimental evidence for three photon processes in UCNPs, particularly for the red emission. Moreover, we demonstrate changes in the excited population dynamics via bi- and triphotonic processes dependent on the environment, surface chemistry, and P, and validate our findings theoretically.
上转换纳米粒子（UCNPs）的合理设计需要更好地了解这些材料中的非辐射猝灭途径。在这里，我们展示了依赖激发功率密度（P）的研究对上转换（UC）发光强度、斜率因子和不同表面化学性质的流行β-NaYF：20% Yb，2% Er UCNPs 在有机溶剂、DO 和水中的绝对量子产率（Φ）的潜力，作为深入了解 UC 机制（包括种群和猝灭途径）的工具，特别是红色发射。我们的测量结果涵盖了三个数量级的 P 范围，揭示了水和有机溶剂中绿光和红光带（I）的 P 依赖性以及 Er 不同发光能级的 P 依赖性种群途径的强烈差异。总之，我们为 UCNPs 中的三光子过程提供了实验证据，特别是对于红色发射。此外，我们通过依赖于环境、表面化学和 P 的双光子和三光子过程证明了激发种群动力学的变化，并从理论上验证了我们的发现。
