Hexagonal NaYF4:Yb3+/Er3+ nanowire arrays were successfully synthesized via a hydrothermal method assisted by AA0 template. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) have been used to study the morphologies and crystal structures of the products. The formation of NaYF4:Yb3+/Er3+ nanowire arrays was investigated in detail, and one possible mechanism was proposed. The hexagonal NaYF4:Yb3+/Er3+ nanowire arrays show characteristic upconversion fluorescence at green( 520-570 nm) and red (630-680 nm) corresponding to the 4f-4f transition of Er3+. Compared with the hexagonal NaYF4:Yb3+/Er3+ microprisms, the intensity of the red light is obviously improved due to size-dependent nonradiative relaxation. (C) 2014 Elsevier B.V. All rights reserved.