Core excitons at theKedge of LiF

The lithium core-exciton spectrum has been reinvestigated with high resolution using synchrotron radiation. Photoelectron yield techniques were employed on evaporated thin films and single crystals cleaved in ultrahigh vacuum. The various observed structures can be well correlated with the results of recent cluster calculations which incorporate multiplet splitting. Photoemission data and the observed band gap are used to estimate the threshold for transitions to the continuum (additivity). The binding energy of the 61.9-eV ${}_{}{}^1{}_{}{}^{}\Gamma _{15}^{}{}_{}{}^{}$ core exciton is found to be 2.1 eV. A lower 58-eV ${}_{}{}^3{}_{}{}^{}\Gamma _1^{}{}_{}{}^{}$ core exciton is observed to have a 6-eV binding energy. In addition, interesting results are obtained which are believed to be due to the generation of point defects ($F$ centers) and aggregates following exposure to intense undispersed synchrotron radiation.