Microstructure and luminescent properties of Eu 3+ -activated MgGa 2 O 4 :Mn 2+ ceramic phosphors

Mn2+ and the trivalent europium (Eu3+)-doped MgGa2O4 ceramics are characterized using a multi-experimental approach. The formation of spinel-structured ceramics is ascertained from X-ray diffraction (XRD) analysis. Morphology investigations with transmission electron microscopy (TEM) show irregularly shaped grains and grain boundaries with a homogeneous distribution of Eu3+ ions. The inability of Eu activator to penetrate the bulk of ceramic grains is inferred from positron annihilation lifetime spectroscopy data. The Eu doping is shown to enhance the positron trapping rate due to the occupancy of vacancy-type defects at ceramic grains by Eu3+ ions. Both Mn2+ and Eu3+ doped samples show a broad multi-color luminescence in 350–650 nm range under 240 nm and 270–300 nm excitations. Blue emission is concluded to originate from host defects, whereas green emission and narrow lines in the red region of the spectrum are attributed to Mn2+ and Eu3+ ions, respectively. High asymmetry around Eu3+ ions can be concluded from the photoluminescence and positron annihilation lifetime spectra analysis.