基于上转换发光材料的多功能集成纳米加热器研究

Photothermal conversion nanomaterial (or optical nanoheater) can be widely used in the fields of biomedicine, microfluidic chips, optical data storage, etc. Upconversion nanoparticles have attracted intense interests due to their unique luminescent property of converting infrared long-wavelength excitation radiation into short-wavelength visible light. Hexagonal NaYF4:Yb3+,Er3+ is one of the most efficient upconversion materials, but the quantum efficiency of NaYF4:Yb3+,Er3+ nanoparticles is lower than 1 %. Most absorption energy is released by down-conversion luminescence or phonon emission.If this part of absorption energy can be converted into heat with high efficiency, upconversion nanoparticles can be developed as novel photothermal conversion nanomaterials which can realize real-time bioimaging and remote temperature monitoring simultaneously. In this project, the energy transfer mechanism of NaYF4:Yb3+,Er3+ nanoparticles will be investigated and the main energy releasing channels will be unveiled. Based on the above results, the influences of host composition, Yb3+/Er3+ concentration, the introduction of doping ions,and surface modification will be studied to improve the abosorption rate and photothermal conversion efficiency. In addition, the core/shell structure will be designed and optimized to control the competition between phothothermal conversion and upconversion luminescence processes. These results can provide theoretical and technical guidance for multifunctional integration of photothermal conversion, upconversion luminescence and temperature sensing on the single-compound upconversion nanoparticle platform. This work will open a new way for the multifunctional integration of upconversion nanoparticles and can contribute to the expanding of their application fileds.

光热转换纳米材料（或称光学纳米加热器）在生物医学、微流控芯片和光学存储等领域有着重要应用。以NaYF4:Yb3+, Er3+为代表的上转换纳米颗粒以其独特的发光性质和诱人的应用前景，成为稀土发光材料领域的研究热点。但上转换纳米颗粒的量子效率较低（<1%），大部分吸收能量以下转换发光或声子发射无效用释放，如将这部分能量高效转换为热，则可开发一种新型的光热转换材料，其同时又具备实时荧光成像和远程温度监控功能。本项目拟以NaYF4:Yb3+,Er3+上转换纳米颗粒为研究对象，在阐明其内部能量转移主要途径的基础上，通过组分调整、核壳结构设计和染料分子表面修饰等手段，提高其光热转换效率和光吸收率，调控光热转换和上转换发光之间的竞争关系，在单一化合物纳米颗粒平台上实现光热转换、上转换发光和温度传感多功能高效集成。本课题将为上转换材料的多功能集成及其应用领域的拓展提供新的思路。

上转换纳米颗粒因其独特的发光特性，在生物医学、光伏电池等领域极具应用前景。上转换纳米颗粒的量子效率较低（<1%），大部分吸收能量以下转换发光或声子发射无效用释放，如将这部分能量高效转换为热，则有望在单一上转换纳米颗粒上同时实现上转换发光、温度传感和光热转换多种功能。本项目在系统研究颗粒尺寸、Yb3+浓度、Er3+浓度、以及其它离子掺杂（Ce3+、Dy3+、Ho3+、Nd3+、Tb3+、Tm3+）对上转换纳米颗粒上转换发光、光热转换和温度传感性能影响规律的基础上，在小尺寸NaGdF4:Yb3+, Er3+（~8nm）单一结构纳米颗粒实现了上转换发光、顺磁性能、温度传感和光热转换等多种功能的集成，可在光热治疗的同时实现温度实时监控和成像实时观察，在生物医学领域具有很好的应用前景。并分别通过“发光”核-“发热”壳的核壳结构设计（解决“发光”过程和“发热”过程的竞争）和染料分子表面修饰（提高纳米颗粒的吸收率），实现了上转换发光和光热转换性能的协同增强。. 此外，超小纳米晶的组分可控制备和低的发光效率仍是制约上转换纳米晶实际应用的关键材料学问题。本项目揭示了β-NaYF4基上转换纳米晶的生长机制，开发了纳米晶尺寸与形貌的有效控制技术，特别是发展了超小（约10nm）β-NaYF4基上转换纳米晶的合成工艺路线。首次发现小尺寸β-NaYF4:Yb3+, Ln3+ (Ln=Er, Tm, Ho) 纳米晶随着温度的升高，具有反常的上转换发光强化现象。并且，这一发光热致增强现象呈现尺寸依赖性。指出了这一反常现象可能与纳米材料内部的声子限制效应有关，这一结果为全面理清决定上转换发光输出的关键因素以及进一步优化上转换纳米晶组分和微结构设计提供了重要思路，并基于此新效应发展了上转换纳米材料在温度颜色指示和新型防伪技术领域的应用。. 项目研究成果为上转换纳米晶的高质量合成、发光性能的改善以及应用领域的拓展提供了新的思路。本项目共发表SCI论文10篇，获得授权专利4项。