In order to quickly identify the upconversion luminescence ability of rare earth doped crystal materials, Yb³⁺/Er³⁺ co-doped MLu_xF_y (M = Li, Na, K, Rb, or Cs; x = 1, y = 4, or x = 2, y = 7) crystal materials were designed and then synthesized using a liquid-solid transfer method. The materials were characterized by using X-ray diffraction, transmission electron microscope, Raman spectroscopy, and fluorescence spectrophotometer. The results indicated that green and red upconversion luminescence of Yb³⁺/Er³⁺ co-doped MLu_xF_y submicron/nanocrystals were obtained under a 980 nm laser excitation, whereas these submicron/nanocrystals differed from one another in their ability to give out upconversion luminescence. In the experiment, a pump power threshold (PPT) was used to quickly distinguish the difference in upconversion luminescence ability of Yb³⁺/Er³⁺ co-doped MLu_xF_y submicron/nanocrystals. According to analysis, it is found that there is a correlation between the PPT and the maximum phonon energies of Yb³⁺/Er³⁺ co-doped MLu_xF_y submicron/nanocrystals. Therefore, in the screening of rare earth doped upconversion luminescent crystal materials, the PPT can be used to quickly identify their upconversion luminescent ability.