Composition‐dependent behavior of Co(d 7 ) optical transitions in Cd 1– x Co x Ga 2 S 4 mixed crystals

The optical transitions due to the cobalt transition metal impurity centers with composition x in C d1– k Co x Ga 2 S 4 mixed crystals were investigated by optical absorption spectroscopy. The optical absorption spectra showed three crystal‐field transitions between the ground state 4 A 2 ( 4 F) and the excited states 4 T 2 ( 4 F), 4 T 1 ( 4 F), and 4 T 1 ( 4 P) of substitutional Co 2+ 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 4 T 1 ( 4 P) 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)