Solubility limit and luminescence properties of Eu3+ ions in Al2O3 powder

Al-Eu-O compounds are synthesized from Al2O3:Eu2O3=(1-x):x mixtures (x=0-0.15) by the metal organic decomposition method and subsequently calcined at various temperatures from Tc=750 to 1200 °C in dry O2 atmosphere. The structural and luminescence properties of these compounds are investigated using X-ray diffraction analysis, photoluminescence (PL) analysis, PL excitation spectroscopy, and luminescence lifetime measurements. The present study focuses on the effects of the Eu2O3 addition (x) on the material and phosphor properties of Al2O3:Eu3+. The stable phase of α-Al2O3 is synthesized at Tc>1100 °C and cubic γ-Al2O3 phase at Tc≤1100 °C. The calcination temperature dependence of the PL intensity yields an activation of Ea~0.8 eV for Eu3+ ions in the Al2O3 host. The luminescence decay time is determined to be ~0.8 ms, independent of x. Temperature dependence of the PL intensity at T=20-450 K exhibits thermal quenching behavior with energies of 17 meV and 0.28 eV at low (<200 K) and high temperatures (>200 K), respectively. The solubility limit of Eu3+ ions in α-Al2O3 is determined to be ~1%. The schematic energy-level diagram of Eu3+ in α-Al2O3 is also proposed for the sake of a better understanding of the luminescence process of this phosphor system.