Deep-UV exciton emission from Mg<subscript>1 − x</subscript>Ca <subscript>x</subscript>O-A first-principle investigation.

In order to investigate the ultraviolet and electron emission properties of rock-salt Mg1 − xCa xO, first-principle calculations are carried out with x ranging from 0 to 0.5. The electron-hole interaction is taken into account by solving the Bethe-Salpeter equation. In pure MgO, the calculated exciton binding-energy value of 83 ± 3 meV is quite close to the published experimental values. The electronic properties of doped MgO are investigated based on the super-cell model. Both the optical bandgap and the exciton binding energy of the super cell of Mg1 − xCa xO are calculated for five discrete compositions, with an increasing amount x of CaO. The results show that there are strong excitonic effects in all of these materials. A rapid reduction in bandgap value is observed for Mg1 − xCa xO, when increasing the x value. The exciton binding energy of Mg1 − xCa xO shows a minimum value of about 40 meV around x = 0.2. In all of these cases, the exciton is stable at room temperature. The lowest excitation levels in Mg1 − xCa xO are determined by dark excitons. The occurrence of these dark excitons might explain why Mg1 − xCa xO is a strong source of delayed electron emission, after being bombarded by ions in a plasma. [ABSTRACT FROM AUTHOR]