Lanthanide doping not only works as sensitizer and activator, but also plays an important role to facilitate the growth of nanocrystal and to control the size, shape, and property of nanocrystals. Here, reported was the synthesis of monodisperse Ba2LaF7 nanocrystals with the size of sub-10 nm through a solvothermal method. We found the dopants of Ho3+, Er3+, or Yb3+ facilitated the growth of Ba2LaF7 nanocrystals obviously to a certain size within a shorter reaction time. Similar phenomenon can also be observed in the synthesis of LaF3 nanocrystals. We find that Ln(3+) (e.g., Ho3+, Er3+, or Yb3+) with smaller radius can reduce the nucleation energy and lead to heterogeneous nucleation, which favors the growth of Ba2LaF7 nanocrystals obviously. In addition, intense upconversion emission can be observed from Ln(3+)-doped Ba2LaF7 nanocrystals under the 980 nm laser excitation, providing great potential application in biological imaging. Especially, Ba2LaF7:Yb/Er (20/1 mol%) nanocrystals present more intense upconversion emission than alpha-NaYF4:Yb/Er (20/1 mol%) nanocrystals under the same conditions. (C) 2011 Elsevier Inc. All rights reserved.