NaYF co-doped with Gd and Mn nanocrystals were synthesized by a solvothermal route with PEI as the surfactant. X-ray diffraction analyses evidenced that the phases of synthesized NaYF : Gd , Mn nanocrystals were all pure cubic structure. The luminescence intensity of 20 mol% Gd doped NaYF was stronger than that of any other concentration under the 272 nm excitation. The photoluminescence emission intensity of NaYF : Gd , Mn at 561 nm was increased with the increase of Gd doping concentration. The energy transfer mechanisms between Gd and Mn were discussed. The results showed that the energy level of P of Gd ions played a key role in the energy transfer process. Furthermore, the Mn ions doped NaYF : Gd nanocrystals with a strong green emission and proper paramagnetism originated from Gd and Mn may find potential applications in bio-probes and magnetic resonance imaging. © 2013 Elsevier B.V.