Luminescence of pure and doped Al2O3 and MgO single crystals under inner-shell excitation

Luminescence properties of pure and doped MgO and Al2O3 single crystals were investigated under excitation by extreme ultraviolet radiation covering the L- and K-absorption edges of cations (Mg, Al) and anion (O), respectively. The excitation spectra of intrinsic and extrinsic emissions are antibate with respect to the absorption at the L-edges in both materials as well as at oxygen K-edge in Al2O3. Such behaviour is explained by non-radiative decay of electronic excitations at the surface. However, the efficiency of free exciton emission (7.6–7.7 eV) shows a positive jump at the oxygen K-edge whereas the recombination impurity emission at 5.4 eV has normal antibate behaviour with respect to the absorption in MgO. The origin of these effects is discussed.