LiYF_4 nanocrystals with tetragonal structure were adopted as the host materials for the phosphors and scintillators owing to the low phonon energy and high optical transparency. LiYF_4:Ln~(3+)(Ce~(3+),Eu~(3+)) nanocrystals were fabricated by solvothermal method. Under UV excitation, they could emit visible light. In order to improve the luminescence intensity, the method of co-doping LiYF_4 nanocrystals with Sc was adopted. Sc~(3+) ions could reduce the lattice expansion caused by the doping of Ce~(3+) or Eu~(3+) whose ionic radius was larger than Y~(3+). Crystal structure of Li(Y,Sc)F_4:Ln~(3+) kept much more stable and the luminescence intensity could be significantly enhanced when the concentration of Sc was a moderate value. Thermoluminescence was employed to analyze the electron traps in Li(Y,Sc)F_4:Ce~(3+). Results suggested that the suppression of the generation of electron traps with the co-doping of Sc contributed to the enhancement of luminescence intensity of LiYF_4:Ce~(3+). LiYF_4: Ln ~ (3 +) (Ce ~ (3 +), Eu ~ (3+)) LiYF_4 nanocrystals with tetragonal structures were the host materials for the phosphors and scintillators due to the low phonon energy and high optical transparency Under order to improve the luminescence intensity, the method of co-doping LiYF_4 nanocrystals with Sc was applied. Sc ~ (3+) ions could reduce the lattice expansion due to the doping of Ce ~ (3+) or Eu ~ (3+) where ionic radius was larger than Y ~ (3+). Crystal structure of Li (Y, Sc) F_4: Ln ~ more stable and the luminescence intensity could be significantly enhanced when the concentration of Sc was a moderate value. Thermoluminescence was employed to analyze the electron traps in Li (Y, Sc) F_4: Ce ~ (3+). Results suggested that the suppression of the generation of electron traps with the co-doping of Sc contributed to the enhancement of luminescence intensity of LiYF_4: Ce ~ (3+) .