Ho3+ with various concentrations and Tm3+ with molar concentration of 1.28% are co-doped in Li YF4(YLF) single crystals. The luminescent properties of the crystals are investigated through emission spectra, emission cross section and decay curves under the excitation of 808 nm. The energy transfer from Tm3+ to Ho3+ and the optimum fluorescence emission of Ho3+ around 2.05 μm are investigated. The emission intensity at 2.05 μm keeps increasing with the molar concentration of Ho3+ improved from 0.50% to 1.51% when the molar concentration of Tm3+ is kept at 1.28%. Moreover, for the co-doped crystals in which the molar concentrations of Tm3+ and Ho3+ are 1.28% and 1.51%, respectively, the maximum emission cross section reaches 0.760×10–20 cm2 and the maximum fluorescence lifetime is 21.98 ms. All the parameters suggest that these materials have more advantages in the future 2.0 μm laser applications. Ho3 + with various concentrations and Tm3 + with molar concentration of 1.28% are co-doped in Li YF4 (YLF) single crystals. The luminescent properties of the crystals are investigated by emission spectra, emission cross section and decay curves under the excitation of 808 nm. The energy transfer from Tm3 + to Ho3 + and the optimum fluorescence emission of Ho3 + around 2.05 μm are investigated. The emission intensity at 2.05 μm keeps increasing with the molar concentration of Ho3 + from 0.50% to 1.51% when the molar concentration of Tm3 + is kept at 1.28%. For the co-doped crystals in which the molar concentrations of Tm3 + and Ho3 + are 1.28% and 1.51%, respectively, the maximum emission cross section reaches 0.760 × 10-20 cm2 and the maximum fluorescence lifetime is 21.98 ms. All the parameters suggest that these materials have more advantages in the future 2.0 μm laser applications.