以枝状聚乙烯亚胺(Branched polyethylenimine，B-PEI)为表面活性剂，水和二乙二醇作为溶剂，采用溶剂热法合成出尺寸为45 nm左右的水溶性B-PEI /NaYF4∶Yb3+, Er3+纳米粒子。在室温980 nm光激发下，样品显示出较强的上转换发光。样品表面的B-PEI分子中的氨基可以连接生物分子。细胞毒性实验显示样品具有较低的细胞毒性。以上结果可以为上转换发光纳米粒子在生物医学领域的应用提供有益的参考。

Branched polyethylenimine (B-PEI) coated NaYF4∶Yb3+, Er3+ nanoparticles with size about 45 nm were successfully prepared via a solvothermal method in water and diethylene glycol using B-PEI as surfactant. The strong upconversion luminescence from the sample can be observed under excitation of 980 nm diode laser at room temperature. The amino groups of B-PEI existing on the nanoparticles can be used for attachment of biomolecules. The cell viability experiments show that the samples have lower cell toxicity. The results presented in this study provide a new insight for the upconversion luminescence nanoparticles in the biomedical applications.