Facile one-pot synthesis of hydrophilic NaYF4:Yb,Er@NaYF4:Yb active-core/active-shell nanoparticles with enhanced upconversion luminescence

• NaYF4:Yb,Er/NaYF4:Yb nanoparticles were prepared by a facile one-pot synthesis strategy.
• They are hydrophilic due to the presence of PVP ligands.
• They exhibit greatly enhanced up-converting luminescence.

We report a facile one-pot synthesis strategy for hydrophilic NaYF4:Yb,Er@NaYF4:Yb active-core/active-shell nanoparticles by two-step injection of ethylene glycol (EG) solution containing different rare earth ions, BF4−, Na+ and Poly(vinylpyrrolidone) (PVP) into EG at 180 °C. NaYF4:Yb,Er@NaYF4:Yb nanoparticles have the size of about 100 nm and cubic-phase structure. The presence of PVP ligands on their surface confers high solubility in water. The aqueous dispersion of these NaYF4:Yb,Er@NaYF4:Yb nanoparticles exhibits greatly enhanced up-converting luminescence, compared with that of NaYF4:Yb,Er core-only nanoparticles and NaYF4:Yb,Er@NaYF4 active-core/inert-shell nanoparticles. Therefore, these hydrophilic NaYF4:Yb,Er@NaYF4:Yb nanoparticles have great superiority as luminescent labeling materials for biological applications.