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

Abstract

A variety of redispersible Eu³⁺-doped LaPO₄ nanoparticles have been prepared in a high-boiling coordinating solvent mixture, and the Eu³⁺ lattice sites of these materials have been investigated by luminescence line-narrowing measurements. In this spectroscopic method, Eu³⁺ 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 LaPO₄ nanoparticles. These sites correspond to those known from bulk LaPO₄. 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 LaPO₄. The surface sites are identical to those obtained by reacting Eu³⁺ with the surface of pure LaPO₄ nanoparticles. The spectroscopic properties of Eu³⁺-doped LaPO₄ nanoparticles differ from those of pure EuPO₄ 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.