Synthesis of Eu3+-doped core and core/shell nanoparticles and direct spectroscopic identification of dopant sites at the surface and in the interior of the particles.

A variety of redispersible Eu(3+)-doped LaPO(4) nanoparticles have been prepared in a high-boiling coordinating solvent mixture, and the Eu(3+) lattice sites of these materials have been investigated by luminescence line-narrowing measurements. In this spectroscopic method, Eu(3+) ions occupying different lattice sites are selectively excited with a tunable narrow-bandwidth laser system and distinguished by their luminescence spectra ("site-selective spectroscopy"). Depending on the concentration of the dopant, up to three different lattice sites could be identified in the interior of the LaPO(4) nanoparticles. These sites correspond to those known from bulk LaPO(4). In addition, a variety of surface sites is observed, which could be converted completely into bulk sites by overgrowing the nanoparticles with a shell of pure LaPO(4). The surface sites are identical to those obtained by reacting Eu(3+) with the surface of pure LaPO(4) nanoparticles. The spectroscopic properties of Eu(3+)-doped LaPO(4) nanoparticles differ from those of pure EuPO(4) nanoparticles, which were also investigated. Remarkably, the core/shell synthesis investigated in this paper allows one to prepare doped nanoparticles that contain no other dopant sites than those known from the corresponding bulk material.