Dopant-Controlled Synthesis of Water-Soluble Hexagonal NaYF4 Nanorods with Efficient Upconversion Fluorescence for Multicolor Bioimaging

A novel strategy is proposed to directly synthesize water-soluble hexagonal NaYF4 nanorods by doping rare-earth ions with large ionic radius (such as La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, and Gd3+), and the dopant-controlled growth mechanism is studied. Based on the doping effect, we fabricated water-soluble hexagonal NaYF4:(Yb, Er)/ La and NaYF4:(Yb, Er)/Ce nanorods, which exhibited much brighter upconversion fluorescence than the corresponding cubic forms. The sizes of the nanorods can be adjusted over a broad range by changing the dopant concentration and reaction time. Furthermore, we successfully demonstrated a novel depth-sensitive multicolor bioimaging for in vivo use by employing the as-synthesized NaYF4:(Yb, Er)/La nanorods as probes.