The fabrication of rare earth luminescent materials with monodispersed and hierarchical morphology is of great importance due to their various applications. In this report, monodispersed hierarchical Yb (OH)(x)F3-x microcrystals assembled by nanorod arrays were synthesized by a mild hydrothermal route. Calcination of Yb(OH)(x)F3-x resulted in the formation of Yb6O5F8 with the retention of morphology. The crystallographic structure relationship between Yb(OH)(x)F3-x and Yb6O5F8 and the transformation mechanism from Yb(OH)J3, to Yb6O5F8 were disclosed. The upconversion emission properties of the Er3+ doped samples were investigated. It can be found that Yb6O5F8: 5%Er3+ exhibited an intense red light upconversion emission with the strongest peaks around 658 nm while Yb(OH)(x)F3-x: 5%Er3+ shows no upconversion emission. (C) 2017 Elsevier Ltd. All rights reserved.