Synthesis and luminescence spectra of two europium(II) aluminates, EuAl2O4 and EuAl12O19

Two europium(II) aluminates, EuAl2O4 and EuAl12O19, were prepared by a solid-state reaction between europium(III) oxide (Eu2O3) and alumina (Al2O3) powders under a mixed H2 and N2 gas flow. In the preparation of EuAl2O4 from a stoichiometric mixture of Eu2O3 and Al2O3, subtle differences in the products, such as whether the Eu4Al14O25 phase co-occurred or not, were observed between δ- and α-Al2O3 powders, which had an effect on the luminescence spectra. Europium(II) aluminates were formed above 1100 °C. A single phase of EuAl2O4 obtained above 1350 °C was confirmed by powder X-ray diffraction, infrared spectroscopy, and 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The 27Al MAS NMR spectrum of EuAl2O4 is reported for the first time. The green emission at 520 nm became more intense with increasing calcination temperatures up to 1300 °C but diminished at higher temperatures. The EuAl12O19 phosphor was also prepared from a stoichiometric mixture of Eu2O3 and Al2O3 at 1200 °C and its luminescence spectrum was compared with that of SrAl12O19:Eu2+.