Functionalized luminescent YVO₄:Ln³⁺ nanoparticles

The synthesis and the emission properties of colloidal YVO₄:Ln nanocrystals (8nm in diameter) are investigated, where Ln = Eu, Nd, Yb, Er. The nanoparticles synthesized here are constituted of a (Y,Ln)VO₄ crystalline core and stabilized by a lanthanide-citrate complexing shell. Surface derivatization of the particles can be achieved through the controlled growth of a silicate shell using a functionalized silane, with elimination of the citrate shell. The luminescence of the Eu³⁺ -doped YVO ₄ colloids is studied in details and compared to the bulk material. Chemical treatments are achieved in order to explain the observed differences. Improvement of the emission quantum yield after the transfer of the colloidal particles into D₂O shows that surface OH groups act as efficient quenchers of the Eu³⁺ emission. The growth of a silica shell around the particles decreases the optimum europium concentration, showing that energy transfers within the nanoparticles are limited by the quenching of the excited states of the vanadate ions. Moreover, site selective excitation spectroscopy seems to prove the coexistence of core sites and surface sites for the europium ions. Finally, colloidal nanoparticles exhibit an emission yield of about 25%, which appears already suitable for some applications.