The first one-pot synthesis of undoped and Eu doped β-NaYF4 nanocrystals and their evaluation as efficient dyes for nanomedicine.

Polygonal-shaped about 75 nm sized and highly crystallized Eu-doped β-NaYF particles were directly prepared under mild conditions using the polyol process. A set of operating parameters were optimized for such a purpose. A conventional heating under reflux for 30 min of a mixture of Y(III) and Eu(III) acetate, ammonium fluoride, sodium hydroxide and oleic acid (OA) dissolved in ethyleneglycol offered a pertinent material processing route if a large excess of NHF and an enough amount of OA were used. Typically, the former parameter provides an exclusive stabilization of the desired β allotropic form, while the latter allows a significant size decrease of the particles. Thanks to their coating by a double OA layer, the produced particles exhibited a hydrophilic surface feature when dispersed in water and when excited under UV light they emitted a very intense red photoluminescence. Additionally, they did not evidence any accurate cytotoxicity when incubated with healthy human foreskin fibroblast (BJH) cells for doses as high as 50 μg·mL and contact time as long as 48 h, highlighting the ability of the prepared particles to be used as efficient down-converter light sources for cell labelling.