Photoluminescence properties of Eu³⁺-doped stalk-like Al₂O₃ via a hydrothermal route followed by heat treatment

Uniform Al₂O₃:Eu³⁺ samples were successfully fabricated via a hydrothermal method and subsequent thermal decomposition of Eu³⁺-doped precursors. The sample characterisations were carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectra. XRD results revealed Eu³⁺-doped samples were a pure γ-Al₂O₃ phase after being calcined at 1173 K. SEM results showed that these Eu³⁺-doped Al₂O₃ samples were stalk-like, with an average length of 1.5 μm. Upon excitation at 394 nm, the orange–red emission bands, having wavelengths longer than 580 nm, were to be from ⁵D₀→⁷F_J (J = 1, 2) transitions. The asymmetry ratio of (⁵D₀→⁷F₂)/(⁵D₀→⁷F₁) intensity is about 0.54, 2.76, 3.29, 2.86, 3.36, 3.13 for Eu³⁺ concentrations of 0.1, 0.4, 0.7, 1.0, 1.5 and 2.0 mol-%, respectively. The optimal doping concentration of Eu³⁺ ions in Al₂O₃ is 1.5 mol-%. According to Dexter's theory, the critical distance between Eu³⁺ ions for energy transfer was determined to be 14 Å.