Resonant absorption and emission from localized core-hole states in Al2O3 and SiO2

We have compared the Al L23 and Si L23 emission and reflection spectra of Al2O3 and SiO2 to obtain information on the nature of the excited states in the presence of the L23 holes. A 5 m Rowland spectrometer, using a 600 l/mm grating mounted in grazing incidence was used to detect both electron excited soft X-ray emission and near normal soft X-ray reflection. We report fine structure in the emission spectra above the L23 edges which coincides with structure in the reflection spectra. These features appear both in the bandgap and in the conduction band. Such features within the bandgap are typically identified as excitons, while those in the conduction band must be localized excited states. Therefore, measurements of ϵ2, for SiO2 and Al2O3 above the L23 edge should be interpreted in terms of localized excitations in the presence of a core hole, rather than interband transitions.