Tan Meiling, Monks Melissa-Jane, Huang Dingxin, Meng Yongjun, Chen Xuewen, Zhou Ying, Lim Shuang-Fang, Würth Christian, Resch-Genger Ute, Chen Guanying
MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering & Key Laboratory of Micro-systems and Micro-structures, Ministry of Education, Harbin Institute of Technology, 150001 Harbin, People's Republic of China.
Nanoscale. 2020 May 21;12(19):10592-10599. doi: 10.1039/d0nr02172e. Epub 2020 May 6.
Single particle imaging of upconversion nanoparticles (UCNPs) has typically been realized using hexagonal (β) phase lanthanide-doped sodium yttrium fluoride (NaYF) materials, the upconversion luminescence (UCL) of which saturates at power densities (P) of several hundred W cm under 980 nm near-infrared (NIR) excitation. Cubic (α) phase UCNPs have been mostly neglected because of their commonly observed lower UCL efficiency at comparable P in ensemble level studies. Here, we describe a set of sub-15 nm ytterbium-enriched α-NaYbF:Er@CaF core/shell UCNPs doped with varying Er concentrations (5-25%), studied over a wide P range of ∼8-10 W cm, which emit intense UCL even at a low P of 10 W cm and also saturate at relatively low P. The highest upconversion quantum yield (Φ) and the highest particle brightness were obtained for an Er dopant concentration of 12%, reaching the highest Φ of 0.77% at a saturation power density (P) of 110 W cm. These 12%Er-doped core/shell UCNPs were also the brightest UCNPs among this series under microscopic conditions at high P of ∼10-10 W cm as demonstrated by imaging studies at the single particle level. Our results underline the potential applicability of the described sub-15 nm cubic-phase core/shell UCNPs for ensemble- and single particle-level bioimaging.
上转换纳米颗粒（UCNPs）的单颗粒成像通常使用六方（β）相镧系掺杂的氟化钠钇（NaYF）材料来实现，在980 nm近红外（NIR）激发下，其功率密度（P）为几百W/cm²时，上转换发光（UCL）会达到饱和。立方（α）相UCNPs在整体水平研究中，由于在可比功率密度下通常观察到较低的UCL效率，大多被忽视。在此，我们描述了一组直径小于15 nm、富含镱的α-NaYbF:Er@CaF核壳结构UCNPs，其掺杂了不同浓度（5 - 25%）的铒，在约8 - 10 W/cm²的宽功率范围内进行研究，即使在10 W/cm²的低功率下也能发出强烈的UCL，并且在相对较低的功率下达到饱和。对于12%的铒掺杂浓度，获得了最高的上转换量子产率（Φ）和最高的颗粒亮度，在110 W/cm²的饱和功率密度（P）下达到了0.77%的最高Φ。如单颗粒水平的成像研究所表明的，在约10⁴ - 10⁵ W/cm²的高功率微观条件下，这些12%铒掺杂的核壳UCNPs也是该系列中最亮的UCNPs。我们的结果强调了所描述的直径小于15 nm的立方相核壳UCNPs在整体和单颗粒水平生物成像方面的潜在适用性。
