利用高温热解法合成了小尺寸、粒径均匀分布的NaYF4∶18%Yb,0.5%Tm纳米晶, 并通过配体交换的方法实现了纳米晶油溶性向水溶性的转变。通过X射线衍射仪、透射电子显微镜和荧光光谱仪对修饰前后的纳米晶进行了结构、形貌和光学性质的表征。实验结果表明：所合成的样品是纯六角相NaYF4(β-NaYF4), 且粒径均匀分布在35 nm左右。在980 nm近红外光激发下, 修饰前后的纳米晶具有强的紫外上转换发射特性, 其Tm3+离子的五光子上转换发光强度强于四光子和三光子上转换发光强度。鉴于这种特殊的光学性质以及小的尺寸, 所合成的水溶性纳米晶在生物医学领域显示出潜在的应用价值。

Uniform NaYF4∶18%Yb,0.5%Tm nanocrystals were synthesized via thermal decomposition method following high temperature, and then a change of the nanocrystals was made from oil-soluble to water-soluble by ligand-exchanged method. X-ray diffraction (XRD) analyses showed that the samples were β-NaYF4 nanocrystals. The TEM images exhibited that the nanocrystals had an average size of 35 nm. Under 980 nm near-infrared laser excitation, the samples showed intense ultraviolet upconversion emission. 5-photon upconversion fluorescence of the Tm3+ ions in the nanocrystals was stronger than 4-photon and 3-photon upconversion fluorescence. Due to special optical properties and small size, the water-soluble nanocrystals would show potential applications in the biomedical field.