Resonant absorption and emission from localized core-hole states in Al 2O 3 and SiO 2

Abstract

We have compared the Al L 23 and Si L 23 emission and reflection spectra of Al 2O 3 and SiO 2 to obtain information on the nature of the excited states in the presence of the L 23 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 L 23 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 ϵ 2, for SiO 2 and Al 2O 3 above the L 23 edge should be interpreted in terms of localized excitations in the presence of a core hole, rather than interband transitions.