Abstract: In present paper luminescent characteristics of Eu (Ⅱ) and Ce(Ⅲ) and their concentra-tion quenching in BaYF₅ are studied. Both ions show d-f excitation and emission. Bycomparison with the values reported before,the quenching concentrations of Eu(Ⅱ) and Ce(Ⅲ)are lower because of the energy migration in Eu(Ⅱ)--Eu(Ⅱ) and Ce(Ⅲ)--Ce(Ⅲ). Thequenching mechanism is acquired by the relation between their emission intensities and theirconcentrations, which is dipole-dipole interaction. The energy transfer from Ce (Ⅲ) to Eu(Ⅱ) was found in the system BaYF₅. A mechanism ot radiationless energy transfer isproposed based on the electric multipole-multipole interaction in the system.There also exista radiative transfer. A possible way for energy transfer is given.

Key words: Barium and Yttrium fluoride, Euripium (Ⅱ), Cerium (Ⅲ), Activation, Luminescence