Facile Synthesis and Controllable Emission of Tm3+/Er3+-Doped and -Co-doped α-NaYbF4 Upconversion Nanocrystals

Tm3+, Er3+-doped and -co-doped alpha-NaYbF4 nanoparticles were synthesized via a facile hydrothermal route with oleic acid as the capping agent. Experimental results showed that the doped NaYbF4 nanoparticles possessed a cubic phase with the average size of similar to 13 nm. Upon excitation by a 980 nm laser, the as-synthesized nanoparticles exhibited blue and red upconversion emissions corresponding to the monodoped Tm3+, Er3+ in the cubic-phase NaYbF4, respectively, and intense green and red emissions in the Tm3+/Er3+-co-doped NaYbF4 nanoparticles. Furthermore, the possible energy transfer mechanism among Yb3+/Tm3+/Er3+ in alpha-NaYbF4 nanoparticles was also proposed. The cell toxicity test revealed that the as-synthesized upconversion nanoparticles possessed remarkably low cytotoxicity. All of the advantageous features including facile synthesis, controllable emission, and low cytotoxicity make the upconversion nanoparticles promising for multicolorbioimaging and anti-counterfeiting applications.