Radiative transitions in irradiated MgAl$_2$O$_4$ spinel crystal

adiative transitions in MgAl2O4 spinel single crystal were investigated after irradiation with He+ ions of fluence ∼1017 particles/cm2. Photoluminescence (PL), PL excitation spectra and PL decay curves were measured at cryogenic temperatures of 8 K. It is shown that PL decay kinetics of 5 eV (250 nm) and 3 eV (420 nm) bands are similar because of the common excited state. Furthermore, after irradiation PL band at ∼5 eV preserved characteristic behaviour of the donor-acceptor pair transitions. The PL channels involve electronic transitions of antisite defects, MgAl (shallow acceptor) and AlMg (shallow donor), and oxygen vacancy VO (deep donor), while AlMg served an intermediate of the electronic excitation channel. The intense emissions were assigned to VO•∗ → VO• (3 eV) and VO•∗ → MgAl× (5 eV), which involve respectively energy and energy-electron transfer. Participation of the doubly-ionized oxygen vacancy VO•• in the energy/electron transfer is suggested. The obtained data enabled a generalised scheme of electronic transitions in MgAl2O4 spinel in presence of intrinsic defects.