Water-soluble Yb3+, Tm3+ codoped NaYF4 nanoparticles: Synthesis, characteristics and bioimaging

Water soluble NaYF4 nanocrystals codoped with 20 mol% Yb3+, 0.5 mol% Tm3+ were prepared by a facile solvothermal approach using polyvinylpyrrolidone (PVP) as a surfactant. The upconversion NaYF4 nanocrystals were pure cubic phase with an average size of ∼40 nm. They could be well redispersed in water to form a clearly transparent solution without obvious precipitation. With the excitation of a 980-nm diode laser, the nanocrystal solution presents bright violet and blue upconversion luminescence. These upconversion nanoparticles (UCNPs) were incubated with HeLa cells at 37 °C for 24 h, and bright blue upconversion luminescence were observed from the UCNPs endocytosed into the HeLa cells on a microscope equipped with a 980-nm fiber laser. These results indicated that the UCNPs had potential applications for biological imaging as luminescent probes.

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► Water soluble NaYF4: Yb3+, Tm3+ nanocrystals were prepared by a solvothermal approach.
► The upconversion nanocrystals were pure cubic phase with an average size of ∼40 nm.
► They could be well redispersed in water to form a clearly transparent solution.
► They were used to label HeLa cells with strong upconversion luminescence.