Synthesis and characterization of efficient near-infrared upconversion Yb and Tm codoped NaYF4 nanocrystal reporter

Efficient near-infrared (NIR) upconversion Yb and Tm codoped NaYF4 nanocrystal reporter was prepared by synthesis at room temperature via wet-chemical route and then heat-treatment at elevated temperature. Several parameters such as pH value of solution, sequence of reactant addition, and annealing temperature, which have strong impacts on the structure and morphology of the nanoparticles, were investigated. Upconversion mechanism and factors that affect the fluorescent performance of the NaYF4:Yb, Tm nanoparticles were discussed. Besides the strong emission around 474 nm, a much more intense emission at about 800 nm was observed emitted by NaYF4:Yb, Tm nanoparticles under 980 nm IR excitation. This strong NIR emission is favorable for the highly sensitive label used in biological detection or in vivo NIR fluorescence imaging.