ELECTRON CORRELATION IN CAF2 STUDIED IN THRESHOLD-EXCITED SOFT-X-RAY FLUORESCENCE

Threshold-excited soft-x-ray-fluorescence spectroscopy has been used to study several selectively excited electronic configurations in CaF2, enabling the determination of specific interaction energies. In the decay of the Ca 2p core excitons via core-to-core fluorescence, final states of the 3s-13d configuration are populated. Here the exchange interaction between the remaining 3s electron and the excited 3d electron was measured, as well as the Coulomb interaction between the core hole and the excited electron. Furthermore, the influence of crystal-field splitting on the 3s-13d states has been studied, and it was found that all of these three interaction energies are interrelated. Using the Ca core-to-core fluorescence data as fingerprints for the 2p excited states, we determine upper limits for the 2p1/2(-1)3d-->2p3/2(-1) Coster-Kronig yields and for the 2p3/2 ionization threshold which in the absorption spectrum is masked by the 2p1/2(-1)3d resonances. Our data are in conflict with optical and photoemission data, a conflict which is resolved by assuming the existence of an excitonic 2p-1ns state unidentifiable in the Ca L absorption spectrum. In the threshold-excited F K fluorescence spectra a satellite is assigned to the decay of core hole states with an additional valence vacancy, making it possible to discuss the p-p correlation energy in the valence band. Finally, the influence on the fluorine valence band of an excitonic screening electron localized in various states primarily localized on the neighboring Ca ions is determined.