Colloidal nanoparticles of Ln3+-doped LaVO4: energy transfer to visible- and near-infrared-emitting lanthanide ions.

Colloidal, organic solvent-soluble Ln3+-doped LaVO4 nanoparticles have been synthesized by a precipitation reaction in the presence of (C18H37O)2PS2- as ligand, that coordinates to the surface of the nanoparticles. The materials are well soluble in chlorinated solvent such as chloroform. Energy transfer of excited vanadate groups has been observed for Ln3+ ions that emit in the visible and the near-infrared (Eu3+, Tm3+, Nd3+, Er3+, Ho3+, Dy3+, Sm3+, Pr3+), thus making it a very generic sensitization mechanism. The LaVO4 nanoparticles have a different crystal structure than bulk LaVO4 ones (xenotime instead of monazite), similar to YVO4 nanoparticles. This xenotime crystal structure results in a more asymmetric crystal field around the Ln3+ ions that is advantageous to their luminescence, for it increases the radiative rate constant, thus reducing quenching processes.