The spectral dependence of the F-center formation efficiency was measured in single crystals, at liquid He and liquid N temperatures, in the vicinity of the K-edge of Br at 13.47keV. The F-center formation efficiency was evaluated by means of optical absorption measurements under irradiation with monochromatic synchrotron X-rays. The efficiency was normalized to the deposited X-ray energy, as estimated by means of sensitive photo-calorimetric measurements. It was found that the F-center formation efficiency exhibited a 24% step-wise increase above the core threshold at liquid He temperatures. It was suggested that the multiple ionization mechanism, following core-hole Auger cascade, might participate actively in the F-center formation process.

M.Yanagihara, S.Hirota, Y.Kondo: Physical Review B, 1996, 53[20], 13386-92