Tb3+ ion doping into Al2O3: Solubility limit and luminescence properties

Abstract

Tb3+-activated Al2O3 phosphors with a molar ratio of are synthesized by metal organic decomposition (x = 0–0.15) and subsequent calcination at Tc = 200–1200 °C for 1 h in air. The material properties of the synthesized phosphors are investigated by X-ray diffraction (XRD), photoluminescence (PL) analyses, PL excitation spectroscopy, and luminescence lifetime measurements. At x = 0.015, the metastable phase of γ-Al2O3 is obtained by calcination at Tc ∼ 300–1050 °C and a mixture of γ, θ, and α phases at Tc ∼ 1050–1150 °C. The high-temperature stable phase of α-Al2O3 is obtained only at Tc ≥ 1150 °C. Below Tc ∼ 300 °C, the XRD data suggest the formation of boehmite (AlOOH). The solubility limit of Tb3+ in α-Al2O3 is also clearly determined to be x ∼ 0.015 (1.5%). The PL decay time of the Tb3+ green emission in α-Al2O3 is ∼1.1 ms for x < 0.015 and slowly decreases with further increase in x (Tb3+). The schematic energy-level diagram of Tb3+ in α-Al2O3 is proposed for a better understanding of the present phosphor system. Finally, the temperature dependence of the PL intensity is examined between T = 20 and 450 K, yielding quenching energies of Eq ∼ 0.28 eV (α-Al2O3 and γ-Al2O3).