Optical Absorption and X-Ray Photoemission Spectra of Lanthanum and Cerium Halides

The fundamental absorption spectra of evaporated thin films of La- and Ce-halides have been measured over a photon energy range from 3 to 40 eV. The fine structures occurring below the threshold in Ce-halides are ascribed to the 4 f →5 d transition of cerium ion. The Cl - L 2,3 absorption spectra of LaCl 3 and CeCl 3 have been measured at room and liquid nitrogen temperatures. Overall profiles of the spectra are alike between the fundamental and Cl - L 2,3 absorption except for the regions near the thresholds. X-ray photoemission spectra of La- and Ce-halides around the valence band have been measured. The occupied 4 f level in CeF 3 is identified to be well above the valence band, whereas it overlaps the valence band partially in CeCl 3 and completely in CeBr 3 . The fundamental absorption spectra are interpreted qualitatively with the aid of obtained Cl - L 2,3 and XPS spectra.