Isobe Ayumu, Takeshita Satoru, Isobe Tetsuhiko
Department of Applied Chemistry, Faculty of Science and Technology, Keio University , 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
Langmuir. 2015 Feb 10;31(5):1811-9. doi: 10.1021/la503652w. Epub 2015 Jan 30.
We synthesized composites of Eu(3+)-doped calcium apatite (CaAp:Eu(3+)) nanoparticles and silica particles via two methods: (i) in situ synthesis of CaAp:Eu(3+) in the presence of silica particles and (ii) electrostatic adsorption of CaAp:Eu(3+) nanoparticles on silica particle surfaces. In both methods, submicrometer spherical silica particles were covered with CaAp:Eu(3+) nanoparticles without forming any impurity phases, as confirmed by X-ray diffractometry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. In method i, part of the silica surface acted as a nucleation site for apatite crystals and silica particles were inhomogeneously covered with CaAp:Eu(3+) nanoparticles. In method ii, positively charged CaAp:Eu(3+) nanoparticles were homogeneously adsorbed on the negatively charged silica surface through electrostatic interactions. The bonds between the silica surface and CaAp:Eu(3+) nanoparticles are strong enough not to break under ultrasonic irradiation, irrespective of the synthetic method used. The composite particles showed red photoluminescence corresponding to 4f → 4f transitions of Eu(3+) under near-UV irradiation. Although the absorption coefficient of the forbidden 4f → 4f transitions of Eu(3+) was small, the red emission was detectable with a commercial fluorescence microscope because the CaAp:Eu(3+) nanoparticles accumulated on the silica particle surfaces.
我们通过两种方法合成了铕（Eu(3+)）掺杂的钙磷灰石（CaAp:Eu(3+)）纳米颗粒与二氧化硅颗粒的复合材料：（i）在二氧化硅颗粒存在的情况下原位合成CaAp:Eu(3+)，以及（ii）将CaAp:Eu(3+)纳米颗粒静电吸附在二氧化硅颗粒表面。通过X射线衍射、傅里叶变换红外光谱和扫描电子显微镜证实，在这两种方法中，亚微米级球形二氧化硅颗粒均被CaAp:Eu(3+)纳米颗粒覆盖，且未形成任何杂质相。在方法（i）中，部分二氧化硅表面充当磷灰石晶体的成核位点，二氧化硅颗粒被CaAp:Eu(3+)纳米颗粒不均匀地覆盖。在方法（ii）中，带正电的CaAp:Eu(3+)纳米颗粒通过静电相互作用均匀地吸附在带负电的二氧化硅表面。无论使用哪种合成方法，二氧化硅表面与CaAp:Eu(3+)纳米颗粒之间的键都足够强，在超声辐照下不会断裂。在近紫外光照射下，复合颗粒呈现出对应于Eu(3+)的4f→4f跃迁的红色光致发光。尽管Eu(3+)的禁戒4f→4f跃迁的吸收系数较小，但由于CaAp:Eu(3+)纳米颗粒聚集在二氧化硅颗粒表面，使用商用荧光显微镜可检测到红色发射。
