The luminescence of Eu2+ in mixed phase system

The dependence of the structure of the hosts on the M ion radius in MMgAl10 O17 (M = Be, Mg, Ca, Sr, Ba, Pb, Eu, Mn, Fe, Co, Ni, Zn, Cd, Sn) system was studied and the luminescence of Eu2+ the mixed phase system was discussed. When M ion radius is less than 0.10 nm, the system MMgAl10O17 constructs b y the mixed phases consisting of manegtoplumbite and spinel, alpha-alumina or spinel and alpha-alumina. In the mixed phase of manegtoplumbite and spin el and alpha-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 al pha-alumina, Eu2+ can enter the lattice site of Mg2+ ion or Al3+ ion and th e d-->f and f-->f transition of Eu2+ can been observed respectively. Meanwh ile, 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. Eu 2+ is partly changed into Eu3+ and the emission of Eu3+ is obviously observ ed even under the condition of reduction atmosphere. If reaction temperatur e is more than 1 150 degrees C, Al2O3 forms alpha-Al2O3 structure, the f--> f transition of Eu2+ appears. If reaction temperature is less than 1 150 de grees C, a mixed phase of alpha-Al2O3 and gamma-Al2O3 is formed, the f-->f transition of Eu2+ disappears and a new band emission from d-->f transition of Eu2+ occurs.