The spectra of transition-metal ions in solids (1975)
AuthorsJohnstone, I.W.show all
The results of an investigation of the Raman and infrared spectra of cobaltous ions in cadmium-chloride, cadmium-bromide, and manganese-chloride, and of cobalt-chloride are presented. The cobalt ions substitute for the cation in these crystals and experience a trigonal crystal-field which splits the lowest ⁴T₁g (⁴F) cubic-field term into six Kramers doublets with energies in the range 0-1200 cm⁻¹. The Raman spectra, measured as a function of temperature and of cobalt concentration show all five single ion electronic transitions together with several lines due to cobalt ion pairs. The infrared spectra comprise both magnetic-dipole allowed electronic transitions and electric-dipole allowed vibronic lines and bands. They confirm the identity of the electronic transitions seen by Raman scattering and also yield information concerning the lattice modes of the host and the possible interactions within cobalt ion pairs. The strong field matrices of the trigonal crystal-field and Zeeman interactions are calculated for the d³ (d⁷) configuration and quantitatively explain the experimental data. The crystal-field analysis provides single ion wavefunctions for further calculations which successfully explain the spectra of antiferromagnetic CoCl₂ and exchange coupled colbalt pairs in CdCl₂ (Co²⁺) and CdBr₂ (Co²⁺). A preliminary investigation of the infrared absorption of an oxygen-induced impurity site in CdCl₂-type crystals is also presented.