Luminescence imaging in the second near-infrared (NIR-II) window, particularly within the NIR-IIb (1500–1700 nm) sub-window, has been utilized for both fundamental research and clinical applications due to its exceptional spatiotemporal resolution. Nevertheless, efficient contrast agents designed for NIR-IIb imaging are still scarce. Herein, a multilayered rare-earth nanocrystal (NaYF:Yb,Er,Ce@NaYF:Yb,Nd@NaYF) with strong NIR-IIb luminescence was designed and synthesized. The doping of Ce ions in the core effectively suppresses the upconversion and boosts the downconversion luminescence by populating the Er I level. Additionally, by separating the sensitizer (Nd) and the activator (Er) in different layers, we are able to maximize the light absorption around 800 nm and reduce the cross relaxations between rare-earth elements, which leads to a strong downconversion emission around 1530 nm under 808 nm excitation. After passivation with NaYF shell and phase transfer with highly PEGylated mesoporous silica layer, the nanocomposites with excellent colloidal stability and bright NIR-IIb emission were obtained. With long blood circulation time in vivo, the fabricated nanocomposites enable high resolution and contrast luminescence imaging of the blood vessels and tumors in living mice. Moreover, the rare-earth nanocrystals with superior optical properties also hold great promise for various applications in optical sensing and biomedical imaging.

中文翻译：

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Nd3+ 敏化多层稀土纳米晶体，具有增强的 NIR-IIb 发光能力，用于高分辨率光学成像


第二近红外 (NIR-II) 窗口中的发光成像，特别是 NIR-IIb (1500–1700 nm) 子窗口内的发光成像，由于其卓越的时空分辨率，已被用于基础研究和临床应用。然而，专为 NIR-IIb 成像设计的高效造影剂仍然稀缺。在此，设计并合成了具有强NIR-IIb发光的多层稀土纳米晶体（NaYF:Yb,Er,Ce@NaYF:Yb,Nd@NaYF）。核心中 Ce 离子的掺杂有效地抑制了上转换，并通过填充 Er I 能级来增强下转换发光。此外，通过将敏化剂 (Nd) 和活化剂 (Er) 分离在不同的层中，我们能够最大限度地提高 800 nm 附近的光吸收，并减少稀土元素之间的交叉弛豫，从而在 1530 附近产生强烈的下转换发射nm 在 808 nm 激发下。经过NaYF壳钝化和高度聚乙二醇化介孔二氧化硅层的相转移后，获得了具有优异胶体稳定性和明亮的NIR-IIb发射的纳米复合材料。由于体内血液循环时间长，所制造的纳米复合材料能够对活体小鼠的血管和肿瘤进行高分辨率和对比度的发光成像。此外，具有优异光学性能的稀土纳米晶在光学传感和生物医学成像等领域也具有广阔的应用前景。