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Laser crystals of LiYF4(LYF) singly doped with Er3 in 2.0% and co-doped with Er3 /Yb3 in about 2.0%/1.0% molar fraction in the raw composition are grown by a vertical Bridgman method. X-ray diffraction (XRD), absorption spectra, fluorescence spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. Compared with the Er3 singly doped sample, obviously enhanced emission at 1.5 μm wavelength and green and red up-conversion emissions from Er3 /Yb3 co-doped crystal are observed under the excitation of 980 nm laser diode. Meanwhile, the emission at 2.7 μm wavelength from Er3 singly doped crystal is reduced. The fluorescence decay time ranging from 18.60 ms for Er3 singly doped crystal to 23.01 ms for Er3 /Yb3 co-doped crystal depends on the ionic concentration. The luminescent mechanisms for the Er3 /Yb3 co-doped crystals are analyzed, and the possible energy transfer processes from Yb3 to Er3 are proposed.