Physicochemical and in situ photoluminescence study of the reversible transformation of oxide ions of low coordination into hydroxyl groups upon interaction of water and methanol with MgO

The interaction of water and methanol with MgO samples with different distributions of oxide ions of low coordination has been investigated by physical techniques, particularly in situ photoluminescence. First, the three photoluminescence fingerprints of oxide ions vs their coordination number have been obtained for samples outgassed at 1273 K. By a pseudo quantitative approach, the relative distribution of the oxide ions of low coordination O2- LC (where LC = 3C, 4C, and 5C refer to tri-, tetra-, and pentacoordinated oxide ions, respectively) was determined and correlated with the shape and size of MgO particles determined by TEM and XRD. The photoluminescence of surfaces of MgO obtained after outgassing at increasing temperature or after interaction of water or methanol with a clean surface, i.e., obtained by outgassing at 1273 K, was then studied and evidenced three other photoluminescent species assigned to surface OH groups. The nature and mechanism of formation of the hydroxyls groups responsible for these new luminescent species are discussed in relation with their thermal stability and FTIR experiments.