In this paper, a solvents-thermal system is developed to prepare one new polymorph of (C2N2H10)(0.5)Ho3F10.chi H2O and rare earth fluorides REF3 nanocrystals under mild condition. It is found that the ionic radius of RE3+ is the key factor responsible for the shape evolution and phase control for rare earth fluorides nanocrystals at selected temperatures, which has an influence on the microstructure and morphology of the products to some extent. With the increase of the atomic number, the shape of fluoride changes from hexagonal REF3 phase (RE = La, Sill) to orthorhombic REF3 phase (RE = Eu-Dy), and finally to diamond structure (C2N2H10)(0.5)Ho3F10.chi H2O (RE = Ho, Er, Tm, Yb, Lu, Y). In addition, the characteristic energy level transition D-5(0)-F-7(1) of Eu3+ splits into 585 and 591 nm emission peaks, and the dominant peak IS the orange emission at 591 nm. (C) 2012 Elsevier Ltd. All rights reserved.