Vibrational and electronic properties of Co(CN)63- doped in alkali halides

The IR spectra of solution grown crystals of NaCl and KCl doped with Co(CN)63- show a multiplet in the v6 stretch frequency region of CN-. Apparently the multiplet consists of four components in NaCl and three in KCl. However, a detailed examination of the results shows that the multiplet consists of several components due to different site symmetries in which Co(CN)63- is present in the crystal. The most probable symmetries are D2h and C8. On x irradiation the multiplet characteristic of Co(CN)63- appear on the low energy side. On heating the crystals, irreversible changes in the spectra occur. The spectra consist of many lines but only the line corresponding to NCO- could be identified. The electronic spectra of the impurity show seven bands in the wavelength region 600 nm to 200 nm as compared with only three bands observed in the solution in this region. The bands are interpreted as being due to transitions of the split components of crystal field levels in Oh symmetry. Both peak positions and intensities are consistent with the assignment.