Luminescence enhancement by the reduction-oxidation synthesis in monoclinic RE2O3 (RE=Eu, Gd) phosphors containing Eu3+ activator

► Synthesis method for enhanced luminescence in monoclinic sesquioxides containing Eu3+. ► Reduction under vacuum with gaseous H2 at 10 Torr and 1300 °C. ► Re-oxidation at 300-1500 °C in air and PL intensities enhanced by ca. 21 times when compared to conventional processing. ► Oxygen vacancy formation by reduction and redistribution by re-oxidation. ► PL decay lifetime increases to 103.6 μs after the re-oxidation from the 23.2 μs.