以柠檬酸三钠为螯合剂, 通过控制反应条件, 利用水热法分别合成出立方相 NaYF4∶Eu3+ 球形纳米粒子和六角相 NaYF4∶Eu3+ 六角微米棱柱。利用X 射线粉末衍射(XRD)、场扫描电子显微镜 (SEM)、红外吸收 (FTIR), 以及发光光谱等手段对产物的物相结构、形貌和荧光性能进行了分析。结果显示产物的晶格结构和柠檬酸分子的选择性吸附是晶体形貌可控的主要原因。在395 nm 光激发下, NaYF4∶Eu3+ 样品显示出较强的橙色 (588 nm)和红色(614 nm) 发光, 分别来自于Eu3+ 离子5D0→7F1和5D0→7F2的跃迁。从5D0→7F2与5D0→7F1 跃迁的强度比可以推断在立方相纳米粒子的晶格中 Eu3+ 离子更多地占据反演中心的格位。

NaYF4∶Eu3+ nanoparticles/hexagonal prism are successfully prepared by hydrothermal method using trisodium citrate as chelator. The obtained samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectra and luminescence spectra. The morphology and crystal structure can be well controlled by adjusting the hydrothermal reaction parameters and the molar ratio of Citrate/Ln. The size of NaYF4∶Eu3+ nanoparticles is about 50 nm, and the size of NaYF4∶Eu3+ hexagonal prism is about 1 000 nm×1 500 nm (side length×thickness). The possible formation mechanism of NaYF4∶Eu3+ nanoparticles/hexagonal prism are proposed based on the experimental results. It was found that the morphology of samples is determined by the intrinsic crystal structure and the selective adsorption of citrate. The FT-IR spectra prove the presence of the citrate ligands at the surface of the nanoparticles/hexagonal prism. Therefore, the NaYF4∶Eu3+ nanoparticles can be dispersed in the water. The NaYF4∶Eu3+ samples exhibit strong orange (588 nm) and red (614 nm) emissions under 395 nm excitation, which are assigned to the 5D0→7F2 and 5D0→7F1 transition, respectively. From the intensity ratio of 5D0→7F2 and 5D0→7F1 transitions, it can be concluded that more Eu3+ ions are occupied the sites of inversion centers in the cubic-phase NaYF4∶Eu3+ nanoparticles.