Investigations on Valence-Change Behaviors of Europium Ions in Eu-Doped Aluminate and Silicate Phosphors

Abstract

Compounds of Sr 3Al 2O 6 : Eu, Sr 4Al 14O 25 : Eu, and BaZnSiO 4 : Eu were synthesized by high-temperature solid state reactions. The doping Eu 3+ ions were partially reduced to Eu 2+ in Sr 4Al 14O 25: Eu and BaZnSiO 4: Eu prepared in an oxidizing atmosphere, N 2 + O 2. However, such an abnormal reduction process could not be performed in Sr 3Al 2O 6 : Eu, which was also prepared in an atmosphere of N 2 + O 2. Moreover, even though Sr 3Al 2O 6: Eu was synthesized in a reducing condition CO, only part of the Eu 3+ ions was reduced to Eu 2+. The existence of trivalent and divalent europium ions was confirmed by photoluminescent spectra. The different valence-change behaviors of europium ions in the hosts were attributed to the difference in host crystal structures. The higher the crystal structure stiffness, the easier the reduction process from Eu 3+ to Eu 2+.