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.
This study is supported by the Ministry of Education and Science of Ukraine under the Young Scientists Program (0117U007189). R. GOLOVCHAK acknowledges the U.S. National Science Foundation (Grant No. DMR-1725188) for the acquisition of PAL spectrometer. J. CEBULSKI acknowledges support from the SAIA for partial support of this research within the National Scholarship Program of the Slovak Republic.
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