Variation in structures and photoluminescence spectra of BaxEu1−xAl2O4 powders

Barium europium(II) aluminate (BaxEu1−xAl2O4) powders were prepared by a solid-state reaction among barium carbonate (BaCO3), europium oxide (Eu2O3), and alumina (Al2O3) powders at 1400 °C for 3 h under a mixed gas flow of H2 and N2. The powders were characterized by powder X-ray diffraction (XRD), infrared and Raman spectroscopy, and photoluminescence (PL). With increasing Ba2+ content in BaxEu1−xAl2O4, the structure of BaxEu1−xAl2O4 changed from a monoclinic (P21) to hexagonal (P63) phase. The hexagonal (P6322) phase was also observed between the two phases. The XRD pattern of a single Ba0.6Eu0.4Al2O4 phase, which has not been reported in the literature, was refined by the Rietveld method and its structure was confirmed by selected-area electron diffraction. With increasing x value, the emission peak in the PL spectra of BaxEu1−xAl2O4 became weaker (x = 0-0.4) and then more intense (x = 0.6-0.98), and its position showed a blue shift from 520 to 498 nm.