Emission of europium(Ⅱ) and europium(Ⅱ) have been observed in SrMgF4:xEu,yTb phosphors which are synthesized in Ar or Ar/H2 flow. The valence state of Eu is influenced by terbium. It is notable that the intensities of the ESR paeaks corresponding to Eu^2^+ are regularly changed when terbium ion is incorporated. The typical Tb3d XPS spectrum belonging to Tb^4^+ is also found when Eu is codoped. This phenomena can be explained by electron transfer mechanism Eu^3^++Tb^3^+→Eu^2^++Tb^4^+. And its equilibrium constant is studied by ESR technique.

Key words: X-RAY DIFFRACTION ANALYSIS, CALCIUM FLUORIDE, MAGNESIUM FLUORIDE, ELECTRON SPIN RESONANCE, EUROPIUM, TERBIUM, BARIUM FLUORIDE, STRONTIUM FLUORIDE, CHARGE-TRANSFER