Photoelectron-spectroscopic determination of lattice self-potentials in lanthanide trifluorides

Abstract

Since the photoelectron spectroscopically measured binding energies probe the potentials at the cation and anion sites separately in solids, they should be a direct determination of the lattice self-potentials at these sites through comparisons with the respective ionization potentials of the gaseous ions. In a study of the photoionization of the 1 s orbital electrons on the fluoride ion and of the outer 5 p or 4 f orbital electrons on the cations of the lanthanide trifluorides, it is found that the so determined lattice self-potentials at the anion sites deviate from those calculated from the electrostatic interactions in the point charge model by an amount which can be explained in terms of ionicity. For the cations, however, the deviations for all except La 3+ and perhaps Gd 3+ exceed those expected for ionicity in the point charge model by as much as 2.3 eV in the case of the maximum at Pr 3+. These deviations are discussed in terms of crystal field interactions, covalency, polarization, and complication caused by final state relaxation during photoionization.