Abstract
Abstract An analysis of photoluminescence and photoexcitation spectra of MgO and CaO powders at 77 K shows that luminescent emission may be associated with low-coordination oxygen ions adjacent to defect sites. In this model luminescent emission involves a charge transfer transition from an electronically excited O2- state to the ground state of the F+ s centre. The corresponding charge transfer transition from ground state O2- ions to F+ s centres is analogous to the α bands observed in the alkali halides, and is responsible for the broad absorption bands near 2 eV observed on γ-irradiation of MgO and CaO powders in vacuo. Involvement of the F+ s (2p) state in quenching of luminescent emission in CaO has been detected. The effect of H2 adsorption in quenching emission has been investigated and can be understood in terms of the derived model for the emission complex.
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