高发光效率的亲水性NaYF4：Yb／Er纳米晶的制备

Preparation of Water-soluble NaYF_4∶Yb/Er Nanocrystals Showing High Upconverting Luminescent Efficiency

以不同比例的乙二醇和水作为混合溶剂,稀土氯化物和NaF为反应物,采用简易的溶剂热法一步制备出亲水性的NaYF4∶Yb/Er纳米晶。用透射电子显微镜、X射线粉末衍射、红外吸收以及发光光谱等测试方法对产物的形貌、物相结构、表面配体和荧光性能进行了表征。结果表明,制备的纳米晶形貌比较均一,主要为立方相和六方相的混合相。随着溶剂中含水量由0%增加到50%,纳米晶尺寸变大,六方相NaYF4∶Yb/Er含量增加,纳米晶的发光强度增加;进一步增加含水量时,尽管纳米晶尺寸变大,六方相含量也相应增加,但是其发光强度降低,可能是由于配体减少引起纳米晶表面缺陷增加,导致发光淬灭。

A simple solvothermal method for preparing hydrophilic NaYF4 ： Yb/Er nanocrystals by changing the ratio of water to ethylene glycol was reported, where rare earth chloride and NaF were used as reactants. The morphology, phase structure, surface ligand and luminescence properties of the NaYF4 ： Yb/Er samples were charac- terized by transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectrum and luminescence spectra. The results indicate the prepared NaYF4： Yb/Er nanocrystals have an uniform morphology and are indexed mainly as a mixture of the cubic and hexagonal phases. Both the size and the content of the hexagonal phases, as well as the emission intensity of the NaYF4 ： Yb/Er nanocrystals go up as the water content in the solvent increases from 0% to 50%. When the water content further increases above 50%, though there is still an increase for the size and the hexagonal phases of the NaYF4 ： Yb/Er nanocrystals, the emission intensity decreases. The initial increase in emission intensity can be associated with the increase in relative amount of hexagonal phase. The subsequent decrease in emission intensity is primarily attributed to the increase of surface defects resulting from the decrease of surface ligands, leading to luminescence quenching.