Calcium difluoride crystals were investigated with ultraviolet-photoelectron spectroscopy, optical absorption spectroscopy, and electron stimulated desorption. Photoemission from ionic crystals like CaF₂ is characterized by some peculiarities that were investigated in detail. Among the investigated effects were the influence of phonons on photoemission (phonon broadening and "quasidirect transitions"), sample charging phenomena, and photoconductivity. It was shown that photoconductivity is caused by thermal detrapping of valence band holes (V_K-centers) created in photoemission. Furthermore, the electronic structure of differently prepared CaF₂ surfaces was investigated, and first UPS measurements from CaF₂ crystals cleaved in UHV are shown. Impurity states on crystals that were cleaved in air and on polished crystals were investigated. By gas dosage experiments, these impurity related states could be assigned to oxygen. Further gas dosage experiments with films of different thickness show that oxygen penetrates the crystal. Changes in the electronic structure of CaF₂ were also induced by electron irradiation (1.5 -2.5 keV) and photon irradiation (21.2eV). During electron irradiation of crystals cleaved in air, the oxygen dissolved in the lattice reacts with calcium metal to form CaO.

Desorption of F⁺ ions from CaF₂ single crystals and epitaxial films was investigated using electrons in the energy range from 0.6 to 3.0 keV. Irradiation resulted in a positively charged sample surface, thus giving an undetermined electrostatic contribution to the F⁺ desorption energies. In this thesis, a method was developed allowing for the first time to measure a positive surface potential of an insulator under electron irradiation. Thus, the kinetic energy of F⁺ ions desorbing from CaF₂ crystals could be corrected for surface charge to determine the energy characteristic for the desorption process. The corrected peak of the F⁺ kinetic energy distribution was at about 0.9 eV for crystals cleaved in UHV. It was shown that coverage of the surface with oxygen or fluorine results in a high positive potential, while metallization causes a low surface potential. In particular, the surface potential of crystals cleaved in UHV shows a pronounced minimum after about 10 to 20 min of electron irradiation. This effect could be explained by a balance of F⁺ desorption and diffusion of fluorine from the bulk.