Study of the crystalline precipitates in NaCl:CoCl2 by optical absorption and Raman spectroscopy

Heat treatments applied to NaCl:CoCl2 mixed crystals have shown the presence of three kind of crystalline precipitates. Both absorption and Raman measurements indicate the presence of CoCl2 in the as grown crystals, whereas upon quenching from different temperatures a tetrahedrally coordinated phase (probably Na2CoCl4) and an octahedrally coordinate one (the Suzuki phase Na6CoCl8) appear. From the resulting crystal field parameters and the phonon frequencies observed both in absorption and Raman spectra information on the structure (particularly the CoCl distance) and the dynamics of the different mixed salt precipitates in obtained, in good agreement with previous results. The study is partially extended to KCl:Co, NaBr:Co and NaBr:Mn.