Optimal Sensitizer Concentration in Single Upconversion Nanocrystals
Optimal Sensitizer Concentration in Single Upconversion Nanocrystals
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DOI：
10.1021/acs.nanolett.6b05331
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发表时间：
2017-05-01
期刊：
影响因子：
10.8
通讯作者：
Jin, Dayong
中科院分区：
文献类型：
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作者：
Ma, Chenshuo;Xu, Xiaoxue;Jin, Dayong
每一个上转换光子晶体（UCNC）通常包含数千个光子敏化剂和数百个光子激活剂，用于将近红外光子上转换为可见光和紫外光。虽然原则上进一步增加敏化剂的浓度将提高吸收效率以产生更亮的纳米晶体，但通常使用20%的Yb 3+离子来避免所谓的“浓度猝灭”效应。在这里，我们报告的浓度猝灭效应不限制敏化剂的浓度和NaYbF4是最明亮的主机矩阵。表面淬灭和大尺寸的NaYbF4纳米晶体是限制这种最佳浓度的唯一因素。因此，我们进一步设计了小模板核之间的NaYbF4的三明治纳米结构，以允许由惰性壳包围的尺寸可调的NaYbF4壳的外延生长，以最大限度地减少表面淬火。结果表明，含有25.2nm三明治结构UCNC的悬浮液比均匀掺杂的UCNC的亮度高1.85倍，并且与类似尺寸的NaYF 4：20%Yb 3+，4%Tm 3 + UCNC相比，每个单一的25.2nm异质UCNC的亮度提高了近3倍。特别地，具有三明治结构的尺寸为13.6和25.2 nm的UCNCs的蓝色发射强度分别是相同尺寸的单片UCNCs的1.36倍和3.78倍。最大化敏化剂浓度将加速更亮和更小的UCNCs作为更有效的生物分子探针或光子能量转换器的发展。
Each single upconversion nanocrystal (UCNC) usually contains thousands of photon sensitizers and hundreds of photon activators to up-convert near-infrared photons into visible and ultraviolet emissions. Though in principle further increasing the sensitizers' concentration will enhance the absorption efficiency to produce brighter nanocrystals, typically 20% of Yb3+ ions has been used to avoid the so-called "concentration quenching" effect. Here we report that the concentration quenching effect does not limit the sensitizer concentration and NaYbF4 is the most bright host matrix. Surface quenching and the large size of NaYbF4 nanocrystals are the only factors limiting this optimal concentration. Therefore, we further designed sandwich nanostructures of NaYbF4 between a small template core to allow an epitaxial growth of the size-tunable NaYbF4 shell enclosed by an inert shell to minimize surface quenching. As a result, the suspension containing 25.2 nm sandwich structure UCNCs is 1.85 times brighter than the homogeneously doped ones, and the brightness of each single 25.2 nrn heterogeneous UCNC is enhanced by nearly 3 times compared to the NaYF4: 20% Yb3+, 4% Tm3+ UCNCs in similar sizes. Particularly, the blue emission intensities of the UCNCs with the sandwich structure in the size of 13.6 and 25.2 nm are 1.36 times and 3.78 times higher than that of the monolithic UCNCs in the similar sizes. Maximizing the sensitizer concentration will accelerate the development of brighter and smaller UCNCs as more efficient biomolecule probes or photon energy converters.