Tunable luminescence and oxygen defects of the spinel MgAl2O4: Eu3+/Eu2+ for photonic application

In this study, we have reported the luminescent property of 0, 0.05, 0.1, and 0.5 mol. % Eu2O3 doped in bulk MgAl2O4 spinel excited at 266 nm. The samples were prepared by slip-cast method and sintered at 1650 °C for 2 h in the air. The sintered samples were subjected to hot isostatic pressing (HIP) in argon atmosphere to achieve theoretical density and transparency. X-ray diffraction patterns for all samples revealed the spinel phase of the face-centered cubic structure. The luminescence of the sintered and HIPed samples was recorded using photoluminescence spectrometers. The sintered samples exhibited characteristic red light emission of Eu3+ at 613 nm. Surprisingly, this Eu3+ emission does not appear for the HIPed samples and shows a characteristic blue emission for the Eu2+ in the 445–480 nm range. Interestingly, further heat treatment of the HIPed samples at 1300 °C for 1 h in air revealed the re-appearance of the characteristic Eu3+ red emission at 613 nm without the Eu2+ blue emission. It is concluded that the Eu3+/Eu2+ emission centers are tunable depending on the processing conditions. Here a characteristic emission center at 482 nm was found for the sintered samples that indicate the presence of oxygen vacancy.