Electronic transitions at the surface of KI microcrystals. Part 1.—Surface states

Abstract

Ultraviolet spectra of sublimated KI films have been taken at room temperature by the diffuse reflectance technique. Besides contributions from the bulk, a broad band centred about 237 nm has been observed, due to surface electronic transitions of an excitonic nature. Annealing treatments and vapour adsorption [H₂O, CH₃OH, (C₂H₅)₂O] show the presence of three overlapping components, related to 5-, 4- and 3-coordinate surface ions. The energies of transition are discussed in terms of the Levine and Mark electrostatic treatment. The component at highest energy is satisfactorily accounted for by the excitation at the {100} faces, whose occurrence in the samples is documented by electron micrographs. The components at lower energies are tentatively assigned to cube edges and vertexes. A brief discussion of the bands formed upon vapour adsorption is also given.