Emission processes in YVO₄:Eu nanoparticles

The luminescence properties of colloidal YVO₄:Eu nanoparticles (8 nm in diameter) are investigated and compared to those of the bulk materials. The emission quantum yield of nanoparticles is improved after the transfer of the colloidal particles into D₂O, showing that surface OH groups act as efficient quenchers of the Eu³⁺ emission. The growth of a silicate shell around the nanoparticles decreases the optimum europium concentration, showing that energy transfers within the nanoparticles are limited by the quenching of the excited states of the vanadate groups. Nanoparticles also exhibit structural distortions directly related to the small size of the particles. No clear evidence is found concerning the influence of these distortions on the energy-transfer processes, since the improvement of the emission properties observed after thermal annealing of both crude and silicated powders seems to result mainly from the elimination of Eu³⁺ and vanadate quenchers from the surface. This latter effect is greatly enhanced in the presence of the silicate shell compared to bare particles.