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 NaYF 4 nanorods by doping rare-earth ions with large ionic radius (such as La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , and Gd 3+ ), and the dopantcontrolled growth mechanism is studied. Based on the doping effect, we fabricated water-soluble hexagonal NaYF 4 :(Yb,Er)/La and NaYF 4 :(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 NaYF 4 :(Yb,Er)/La nanorods as probes.