Composition-dependent behavior of Co(d7) optical transitions in Cd1-x Cox Ga2S4 mixed crystals

The optical transitions due to the cobalt transition metal impurity centers with composition x in Cd1–k Cox Ga2S4 mixed crystals were investigated by optical absorption spectroscopy. The optical absorption spectra showed three crystal‐field transitions between the ground state 4A2(4F) and the excited states 4T2(4F), 4T1(4F), and 4T1(4P) of substitutional Co2+ ions that were similar for all the investigated compositions. The crystal‐field parameter (Dq ) and the Racah parameter (B ) obtained from the observed absorption bands showed a composition dependence such that the Dq parameter increases; on the other hand, the B parameter decreases with increasing composition x, which implies that the Racah parameter (B ) depends strongly on the host crystal. Also, the total splitting between the highest and the lowest states of the 4T1(4P) state split due to spin–orbit coupling showed a composition dependence varying from 1576 cm–1 to 1232 cm–1 with increasing x . The spin–orbit coupling parameter γ varied from 394 cm–1 to 308 cm–1 with composition x . (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)