title: Composites of Eu(3+)-doped calcium apatite nanoparticles and silica particles: comparative study of two preparation methods.
abstract: 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.
authors.affiliation: Department of Applied Chemistry, Faculty of Science and Technology, Keio University , 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
authors.forename: Ayumu
authors.initials: A
authors.lastname: Isobe
authors.forename: Satoru
authors.initials: S
authors.lastname: Takeshita
authors.forename: Tetsuhiko
authors.initials: T
authors.lastname: Isobe
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D005063:Europium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D049408:Luminescent Agents / Q000737:chemistry*; D008163:Luminescent Measurements; D008856:Microscopy, Fluorescence; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D049408:Luminescent Agents; D005063:Europium; D012822:Silicon Dioxide; D002118:Calcium