Single YVO₄:Eu nanoparticle emission spectra using direct Eu³⁺ ion excitation with a sumfrequency 465-nm solid-state laser

We report emission spectrum measurements on single Y_xEu _1-xVO₄ nanoparticles. The inhomogeneous widths of the emission peaks are identical for single nanoparticles and for ensembles of nanoparticles, while being broader than those of the bulk material. This indicates that individual nanoparticles are identical in terms of the distribution of different local Eu³⁺sites due to crystalline defects and confirms their usability as identical, single-particle oxidant biosensors. Moreover, we report a 465 nm solid-state laser based on sum-frequency mixing that provides a compact, efficient solution for direct Eu³⁺ excitation of these nanoparticles. Both these two aspects should broaden the scope of Eu-doped nanoparticle applications.