RESONANT PHOTOEMISSION-STUDIES OF THULIUM MONOCHALCOGENIDES AROUND THE TM 3D THRESHOLD

We have studied 4f photoemission spectra of thulium monochalcogenides at excitation photon energies of the 3d-4f resonance region (hv = 1450 -1520 eV). The experimental results are compared with theoretical calc ulations. The contributions from the 4f divalent part and the trivalen t part in the 3d-4f resonance are more clearly distinguished and resol ved than for the 4d-4f resonant photoemission. The calculated results are in good agreement with the experimental ones both for divalent and trivalent features of thulium ions. We have estimated the mean valenc e of TmS, TmSe and TmTe samples from 3d absorption spectra and from of f-resonant photoemission spectra. The latter should reflect more bulk- sensitive information than that reported for the 4d-4f resonance regio n. It is concluded that the 3d-4f resonant photoemission is a more use ful technique to investigate 4f electronic structures than the 4d-4f p hotoemission, when we perform the experiments with relatively higher e nergy resolution. (C) 1998 Elsevier Science B.V.