一步水热法合成兼具上转换发射增强和双模发射的NaYF4∶Yb3+,RE3+@CDs纳米复合材料

One-Step Synthesis of NaYF4∶Yb3+，RE3+@CDs Nanocomposites with Enhanced Up-Conversion Emission and Dual-Mode Emission

摘要:

稀土离子(RE³⁺)掺杂上转换发射材料因具有优异的光学性能，在生物医学、离子检测、荧光传感和防伪等领域显示出巨大的应用潜力。碳点(CDs)作为一类新型的碳纳米材料，可以与稀土掺杂构建复合材料，通过将不同材料的优势结合，展现出纳米复合材料独特的性质和功能。然而，现有研究制备的复合材料均为大尺寸，限制了其多功能应用，纳米复合材料合成策略亟需进一步的研究和完善。将柠檬酸和尿素制备的CDs添加到NaYF₄∶Yb³⁺,RE³⁺的前驱体溶液中，通过一步水热法制备了NaYF₄∶Yb³⁺,Er³⁺@CDs纳米复合材料，采用XRD、TEM、FT-IR和XPS等表征手段深入研究了CDs对其结构和发射性能的影响。研究发现，CDs成功附着在NaYF₄∶Yb³⁺,RE³⁺表面，NaYF₄∶Yb³⁺,RE³⁺样品是具有立方相的单分散纳米球，CDs的引入未改变纳米复合材料中NaYF₄∶Yb³⁺,RE³⁺的晶型。NaYF₄∶Yb³⁺,RE³⁺@CDs纳米复合材料表现出优异的双模发射性能，分别归因于CDs的下转换发光和RE³⁺掺杂离子的上转换特征发射。同时，CDs的引入使RE³⁺上转换发射增强，其增强机制可能是：（1）通过CDs表面羧基与RE³⁺的强配位，CDs成功钝化了NaYF₄部分表面缺陷；（2）利用CDs吸收激发电子，并将能量转移到RE³⁺的较低能级，形成激发电子的富集。这种发光增强策略对于不同的掺杂离子(NaYF₄∶Yb³⁺,Er³⁺、NaYF₄∶Yb³⁺,Tm³⁺和NaYF₄∶Yb³⁺,Ho³⁺)也同样具有显著的增强效果。本研究结果为进一步改善RE³⁺掺杂上转换发射材料的发光性能提供了一种简单且有效的新合成策略。

Abstract:

Rare earth ions （RE³⁺） doped up-conversion luminescent materials have shown great potential for applications in biomedicine， fluorescence sensing， ion detection， and anti-counterfeiting due to their excellent optical properties. In this paper， we reported a facile synthetic strategy to synthesize NaYF₄∶Yb³⁺，RE³⁺@CDs nanocomposites via hydrothermal synthesis by adding CDs prepared with citric acid and urea as precursors to a precursor solution of NaYF₄∶Yb³⁺，RE³⁺. The successful attachment of CDs on the surface of NaYF4∶Yb³⁺，RE³⁺ was confirmed by XRD， TEM， FT-IR ， XPS and other characterization methods. It was found that the as-prepared NaYF₄∶Yb³⁺，RE³⁺ were uniform monodisperse nanospheres，and the crystal form of NaYF₄ in the nanocomposite is not altered by CDs. Under the excitation of UV light， the prepared NaYF₄∶Yb³⁺，RE³⁺@CDs nanocomposites exhibit excellent dual-mode emission properties attributed to down-conversion emission of CDs and up-conversion characteristic emission of RE³⁺-doped ions， respectively. Meanwhile， the addition of CDs has led to enhanced RE³⁺ up-conversion emission. It may be due to （1） the successful passivation of some surface defects of NaYF₄ due to the strong coordination ability of the COOH on the surface of CDs with RE³⁺ ions； and （2） CDs are used to absorb excited electrons and transfer energy to the lower energy level of RE³⁺， resulting in the enrichment of the excitation electrons. This strategy is also effective for different doping ions （NaYF₄∶Yb³⁺，Er³⁺， NaYF₄∶Yb³⁺，Tm³⁺ and NaYF₄∶Yb³⁺，Ho³⁺）. The results of this study provide a simple and effective new synthesis strategy for further improving property of other RE³⁺-doped up-conversion luminescent materials.