Photoluminescence properties of the Eu-doped alpha-Al2O3 microspheres

• Al2O3:Eu3+ phosphors were prepared via a microwave solvothermal route.
• The particles were hierarchically nanostructured microspheres packaged by nanosheets.
• The powders presented excellent orange–red emission when excited at 393 nm.
• Critical concentration and distance of Eu3+ in Al2O3 is 0.007, 18 Å, respectively.

Al2O3:Eu3+ samples were synthesized via microwave solvothermal method and thermal decomposition of Eu3+ doped precursors. The sample characterizations were carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL) spectra. XRD results indicated that Eu3+ doped samples were most of α-Al2O3 phase after being calcined at 1473 K. SEM results showed that the obtained α-Al2O3 based powders via microwave solvothermal method were microspheres with an average diameter about 1.6 μm. PL spectra showed that upon excitation at 393 nm, the orange–red emission bands at the wavelength longer than 560 nm were from 5D0 → 7FJ (J = 1, 2) transitions. The asymmetry ratio of (5D0 → 7F2)/(5D0 → 7F1) intensity is about 1 and this value suggests that Eu3+ ions occupy the same ratio of symmetry and asymmetry sites. It is shown that the 0.7 mol% of doping concentration of Eu3+ ions in α-Al2O3:Eu3+ is optimum. According to Dexter’s theory, the critical distance between Eu3+ ions for energy transfer was determined to be 18 Å.