915nm激发基于局域场及能量传递机制调控增强NaScF4:Yb3+/Er3+纳米晶上转换红光的研究

Hexagonal NaScF4: Yb3+/Er3+ nanocrystal (NC) is an efficient red upconversion (UC) material. Through UC luminescence modulation in this material, it is promising to obtain more effective red UC emission, resulting in the improvement of the penetration depth in biological tissues and the efficiency of photodynamic therapy. However, as far as we know, there are only a few papers in the literature concerning the UC luminescence modulation in hexagonal NaScF4: Yb3+/Er3+ NCs. In this project, we aim to realize UC enhancement or even red UC selective enhancement in hexagonal NaScF4: Yb3+/Er3+ NCs through varying the molar ratio of Na+ and Ln3+ to produce Na+ and F- vacancies or doping transition metal ions, which can decrease the local crystal field symmetry and change the energy transfer mechanism. In addition, since the absorption efficiency of water molecules at 915 nm is about 15.67% of the value at 980 nm, 915 nm is employed as the excitation wavelength to avoid the serious biological tissues overheating caused by 980 nm irradiation and improve the penetration depth in biological tissues. The specific research contents are as follows: explore the influence of the molar ratio of Na+ and Ln3+ changing and transition metal ions doping on the crystalline phase, morphology and size of the NCs; study the UC luminescence and energy transfer mechanism along with the dynamic processes of the prepared materials by luminescence theory and spectroscopy techniques to reveal the reason of UC enhancement. Much more importantly and valuably to be addressed, our proposal is aiming at establishing the physical and experimental basis of biological applications of hexagonal NaScF4: Yb3+/Er3+ NCs with high efficient red UC emission.

六角相NaScF4:Yb3+/Er3+纳米晶是一种高效的上转换红光材料，对其进行荧光调制将有望得到更加高效的红色上转换发光，从而增加在生物组织中的穿透深度、提高光动力治疗的效率，但目前相关的报道却非常之少。在本项目中，将通过调节Na+/Ln3+比例以产生Na+与F-空位或掺杂过渡金属离子的手段，降低晶场对称性并改变能量传递机制，以实现其上转换发光增强甚至是红光选择性增强。另外，为避免980nm激发所引起的生物组织过热现象、增加在生物组织中的探测深度，本项目将选取915nm作为激发波长，水分子在该处的吸收效率仅为980nm处的15.67%。具体研究内容如下：探索Na+/Ln3+比例变化和过渡金属离子掺杂对纳米晶的晶相、形貌及颗粒尺寸的影响；利用发光学原理及光谱技术手段，着重研究材料的发光性质及动力学过程，揭示上转换增强的本质原因。为获得生物适用的高效红光发射NaScF4纳米材料奠定理论基础。

对于上转换材料而言，在其激发光源为近红外光的前提下，如果将发射光的波长调节到650 nm - 680 nm的红光区域，不仅可以增加纳米颗粒在生物组织中的穿透深度，还可以提高光动力治疗的效率。围绕这一研究目标，我们展开了本项目的研究工作，并进行了一定的扩展，取得的一系列研究成果如下：首先，按照本项目的预定计划，采用溶剂热法合成了纯的六角相NaScF4: Yb3+/Er3+纳米颗粒，并通过Mn2+掺杂实现了上转换红光增强，增强倍数约为7.5倍。同时，凭借稳态/瞬态光谱测试手段并结合能量传递及发光学原理，成功地揭示了其上转换发光增强的机理。其次，通过对衰减曲线及稳态方程进行详细地分析，获得了915 nm激发下Er3+: 4F9/2红光能级的布居途径。再次，获得了BaY2O4: Yb3+/Er3+和CaO-Y2O3: Yb3+/Er3+两种高效的红色上转换发光材料，并对其在可见及近红外区的温敏特性进行了细致的分析。另外，我们还详细地研究了LuVO4: 20% Yb3+/2% Er3+中热耦合的Er3+: 2H11/2/4S3/2能级的荧光温敏特性，在所研究的温度范围内其绝对灵敏度可达到0.82% K-1，相对灵敏度可达到1.12% K-1。. 本项目执行期间，共计在Talanta，Inorganic Chemistry，Journal of Alloys and Compounds，Journal of the American Ceramic Society等期刊发表SCI论文21篇，申请国家发明专利1项，培养研究生6名，圆满地完成了本项目的研究任务。