Oxygen-Vacancy-Induced Midgap States Responsible for the Fluorescence and the Long-Lasting Phosphorescence of the Inverse Spinel Mg(Mg,Sn)O₄

Samples of inverse spinel Mg 2 SnO 4 were prepared using a ceramic method, their phosphorescence phenomenon was probed by optical measurements, and its cause was explored on the basis of density functional theory calculations for model structures of Mg 2 SnO 4 with oxygen vacancies V O . Mg 2 SnO 4 exhibits long-lasting luminescence at two different wavelength regions, peaking at ∼498 and ∼755 nm. A Sn-V O -Sn defect plus a Mg vacancy V Mg away from the V O generates the empty midgap states, σ Sn-Sn and σ Sn-Sn *, localized at the Sn-V O -Sn defect, while an oxygen vacancy V O between adjacent Sn 4+ and Mg 2+ sites creates a filled midgap state Sn 2+ (5s 2 lone pair) lying below the σ Sn-Sn level. The long-lasting luminescence at two different wavelength regions and the up-conversion photostimulated luminescence observed for undoped Mg 2 SnO 4 are well explained by considering the σ Sn-Sn * level as the trapping level for a photogenerated electron.