Luminescent properties of europium-doped (H3O)Y3F10•xH2O nanocrystals

Low-polydispersity europium-doped (H3O)Y3F10 center dot xH(2)O single-crystal nanoparticles can be prepared via a simple reverse microemulsion method. The doping level of the particles can be varied by changing the relative concentration of europium to yttrium in the initial precursor mixture. Doping levels of up to 14 +/- 2 at% can be attained without loss of the host crystal structure. Final europium concentrations, however, fall below those of the precursor solutions, suggesting that europium ions are less readily incorporated into the (H3O)Y3F10 center dot xH(2)O crystal lattice than are yttrium ions. Emission spectra of the doped nanoparticles show sharp well-defined lines, which can be assigned to known europium transitions. The emission intensity increases linearly with increasing europium content. Europium ions within the nanocrystals exhibit excited-state lifetimes of 3-5 ms. These values are an order of magnitude greater than those of free ions in solution, indicating that ion incorporation in the yttrium fluoride matrix efficiently reduces non-radiative energy losses. Finally, data from time-resolved phosphorescence measurements suggests that europium ions within the particles are located in spectroscopically different environments which can be tentatively assigned to surface and core sites.