Atmospheric plasma-assisted modification of nanosized LiYF₄:Eu³⁺ with gold nanoparticles

Both gold and rare-earth doped fluoride nanoparticles have been drawing interest for their possible biological applications, for therapy or for bioimaging. Gold nanoparticles can be used as a heat source for photothermal therapy, absorbing energy through its surface plasmon resonance (SPR) band and converting it to heat, whereas the low phonon energy, long emission lifetimes and sharp emission lines of the fluoride nanoparticles can circumvent several drawbacks of other used materials for bioimaging. In this context, this article proposes a modification of nanosized europium doped-LiYF₄ with gold nanoparticles using a helium atmospheric plasma to reduce Au³⁺ to form the gold nanoparticles. In this article, we successfully synthesized citrate stabilized gold nanoparticles assisted by a helium atmospheric plasma, which showed a broad size distribution between 30 and 109 nm and different shapes, and a SPR band at 544 nm. We also successfully modified LiYF₄:Eu³⁺ with gold nanoparticles with the atmospheric plasma jet, which presented a SPR band at 539 nm and significantly suppressed europium luminescence possibly due to the absorption of the emitted photons of the Eu³⁺ by the gold SPR band.