Synthesis of biocompatible and luminescent NaGdF₄:Yb,Er@Carbon nanoparticles in water-in-oil microemulsion

Here we present a microemulsion route to prepare core-shell structured NaGdF4:Yb,Er@Carbon nanoparticles, in which a thin layer of hydrophilic carbon was covered on hydrophobic NaGdF4:Yb, Er nanocrystals. The prepared NaGdF4:Yb,Er@Carbon nanoparticles were uniform in a size of 25 nm, water-dispersible, and displayed good biocompatibility and strong upconversion fluorescence. Their potential for use as efficient cell-imaging probes is also demonstrated.