Abstract: The dependence of the structure of the hosts on the Mion radius in MMgAl₁₀O₁₇(M=Be, Mg, Ca, Sr, Ba, Pb, Eu, Mn, Fe, Co, Ni, Zn, Cd, Sn) system was studied and the luminescence of Eu²⁺in the mixed phase system was discussed. When Mion radius is less than 0.10nm, the system MMgAl₁₀O₁₇constructs by the mixed phases consisting of manegtoplumbite and spinel, α-alumina or spinel and α-alumina. In the mixed phase of manegtoplumbite and spinel and α-alumina, Eu²⁺ion preferentially occupies lattice site of the cations in manegtoplumbite well matched with the radius and charge of Eu²⁺. There exists only d→f transition emission of Eu²⁺and no characteristic emission of Eu³⁺occurs in those hosts. In the mixed phase of spinel and α alumina, Eu²⁺can enter the lattice site of Mg²⁺ion or Al ³⁺ion and the d→f and f→f transition of Eu²⁺can been observed respectively. Mean-while, since the radius and charge of matrix lattice ions substituted by Eu²⁺do not match with those of Eu²⁺, the valence state of Eu²⁺is unstable. Eu²⁺is partly changed into Eu³⁺and the emission of Eu³⁺is obviously observed even under the condition of reduction atmosphere. If reaction temperature is more than₁150 ℃, Al₂O₃forms α-Al₂O₃structure, the f→f transition of Eu²⁺appears. If reaction temperature is less than₁150 ℃, a mixed phase of α-Al₂O₃and γ-Al₂O₃is formed, the f→f transition of Eu²⁺disappears and a new band emission from d→f transition of Eu²⁺occurs.

Key words: Europium, Mixed phase system, Luminescence, Valence state stability