Composites of Eu3+-Doped Calcium Apatite Nanoparticles and Silica Particles: Comparative Study of Two Preparation Methods

We synthesized composites of Eu3+-doped calcium apatite (CaAp:Eu3+) nanoparticles and silica particles via two methods: (i) in situ synthesis of CaAp:Eu3+ in the presence of silica particles and (ii) electrostatic adsorption of CaAp:Eu3+ nanoparticles on silica particle surfaces. In both methods, submicrometer spherical silica particles were covered with CaAp:Eu3+ 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:Eu3+ nanoparticles. In method ii, positively charged CaAp:Eu3+ nanoparticles were homogeneously adsorbed on the negatively charged silica surface through electrostatic interactions. The bonds between the silica surface and CaAp:Eu3+ nanoparticles are strong enough not to break under ultrasonic irradiation, irrespective of the synthetic met...