Optical and Photoelectrical Studies of the Energy Levels of CoX₄²⁻ in K₂CoX₄ and RbCoX₃ (X≡Cl or Br)

Abstract

It has been found that the optical absorption spectra of CoX₂(X≡Cl or Br) evaporated on substrates of KX or RbX change drastically when samples are annealed above 70°C. An analysis of X-ray photoemission lines of core levels indicates that the change is caused by the formation of a new compound as K₂CoX₄ or RbCoX₃. The chemical reactions, CoX₂+KX→K₂CoX₄ and CoX₂+RbX→RbCoX₃, proceed fast above 80°C. The major results include the intense crystal-field bands in the 1.5–2 eV region arising from 3d electrons of Co²⁺ occupying tetrahedral sites and the p→d charge-transfer bands above 4 eV, as well as the X-ray photoemission spectra of valence electrons. The f-values of the d→d transitions are of the order of 10⁻³. All of the observed spectra are interpreted in terms of the localized excitation in a CoX₄²⁻ complex-ion.