Highly efficient multicolor up-conversion emissions and their mechanisms of monodisperse NaYF4:Yb,Er core and core/shell-structured nanocrystals
Highly efficient multicolor up-conversion emissions and their mechanisms of monodisperse NaYF4:Yb,Er core and core/shell-structured nanocrystals
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单分散NaYF4:Yb,Er核和核/壳结构纳米晶的高效多色上转换发射及其机理
DOI：
10.1021/jp073920d
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发表时间：
2007-09-20
影响因子：
3.7
通讯作者：
Yan, Chun-Hua
中科院分区：
文献类型：
--
作者：
Mai, Hao-Xin;Zhang, Ya-Wen;Yan, Chun-Hua
本文综述了单分散NaYF4：YB，Er核(α和β-NaYF4：YB，Er)和核/壳(α-NaYF4：YB，Er@α-NaYF4和β-NaYF4：YB，Er@α-NaYF4)纳米晶的高效多色上转换(UC)发射及其相关机制，这些纳米晶具有可控的尺寸(α相纳米晶为5-14NRA，β相纳米晶为20-300 nm)、化学成分和表面状态。这些纳米粒子是以三氟乙酸酯为前驱体，在油酸/油胺/十八烯的热溶液中通过独特的延迟成核途径合成的。在980 nm激光(功率密度1.22 W cm(-2))激发下，在980 nm激光(功率密度1.22 W cm(-2))激发下，在所制备的纳米晶(1wt%)的环己烷分散体系中，在肉眼和自然光下可以观察到强烈的多色UC发射(红、黄、绿，无滤光片)。在对β-NaYF4：Yb，Er纳米晶进行成分优化的基础上，得到了绿光与红光的强度比(f(g/r))约为30，为我们所知的最高值。高效的多色UC发射是由受控的微晶尺寸、物相和相关的缺陷状态引起的。β-NaYF4：YB，Er和大的β-NaYF4：YB，Er纳米晶在980 nm的近红外激光激发下表现出正常的双光子UC过程，而小的P-NaYF4：YB，Er纳米晶表现出不寻常的部分三光子过程。成壳可以显着减少表面缺陷和表面配体的影响，从而减少相关的非辐射衰变。结果表明，核/壳结构的α-NaYF4：YB，Er@α-NaYF4和β-NaYF4：YB，Er@α-NaYF4纳米晶的绿光发射强度、fg/r和饱和功率都有很大的提高。合成的NaYF4：Yb，Er核/壳纳米晶具有显著的发光性能，是极具理论意义和实用价值的发光材料。
This paper comprehensively presents the highly efficient multicolor up-conversion (UC) emissions and related mechanisms of monodisperse NaYF4:Yb,Er core (alpha- and beta-NaYF4:Yb,Er) and core/shell (alpha-NaYF4:Yb,Er@alpha-NaYF4 and beta-NaYF4:Yb,Er@alpha-NaYF4) nanocrystals with controlled size (5-14 nra for alpha-phase nanocrystals and 20-300 nm for beta-phase nanocrystals), chemical composition, and surface state. These nanoparticles were synthesized via a unique delayed nucleation pathway using trifluoroacetates as precursors in hot solutions of oleic acid/oleylamine/1-octadecene. With the naked eye and natural light the intense multicolor UC emissions (red, yellow, or green, without filters) can be observed in cyclohexane dispersions of as-prepared nanocrystals (1 wt%) excited by a 980 nm laser source (power density 1.22 W cm(-2)). On the basis of compositional optimization for beta-NaYF4:Yb,Er nanocrystals, the intensity ratio of green to red emission (f(g/r)) reaches ca. 30, the highest value to our knowledge. The highly efficient multicolor UC emissions were aroused from the controlled crystallite size, phase, and associated defect state. beta-NaYF4:Yb,Er and large beta-NaYF4:Yb,Er nanocrystals displayed a normal two-photon UC process excited by a 980 nm NIR laser, while small P-NaYF4:Yb,Er nanocrystals showed an unusual partially three-photon process. Shell formation could remarkably decrease the surface defects and surface ligands influence and thus decrease the associated nonradiative decays. As a result, the core/shell-structured alpha-NaYF4:Yb,Er@alpha-NaYF4 and beta-NaYF4:Yb,Er@alpha-NaYF4 nanocrystals exhibited greatly enhanced green emission intensity,fg/r, and saturation power with respect to their counterparts. The remarkable UC properties of the as-synthesized NaYF4:Yb,Er core and core/shell nanocrystals demonstrate that they are promising UC nanophosphors of adequate theoretical and practical interest.