This work presents the luminescent properties of Ho3+/Tm3+ co-doped Na5Lu9F32 single crystals that were grown by an improved Bridgman method for the first time. The J-O intense parameters of Ho3+ ions were calculated. An intense 2.0 mu m emission was achieved with Tm3+ ions sensitizing Ho3+ ions by the processing of energy transfer from Tm3* ions to Ho3+ ions under excitation of 800 nm LD. The maximum emission intensity at 2.0 um is obtained, and the cross sections of Tm3+ ions and Ho3+ ions were calculated. The physical mechanism for energy transfer from Tm3+ to Ho3+ ions was analyzed by using Inokuti-Hirayama's model. (C) 2016 Elsevier B.V. All rights reserved.