Abstract: In this paper the narrow line emision of f→f transition for Eu²⁺ ion in the system BaF₂-xREF₃ (RE:rare earths) is reported.When RE=Lu,x=1 (at temperature T=300K); RE=Y,x=2(T=300K)'RE=Sc,x=2(T=77K);RE=La or Gd(T=77K) the narrow line emission was found to be dependent on the temperature (T) and the molar ratio (x) between cations in flouride matrix and the emission became more easier according the order of La, Gd, Sc, Y and Lu. No narrow line emission for Eu²⁺ ion in BaF₂-xLnF³ (Ln=lanthanide ions except Pm) was observed, irrespective of whatever molar ratio ortemperature was used in the experiments.The narrow line emission (f→f) has been ascribed to the weak crystal field at the site of the Eu²⁺ ion in fluorides.