Optical absorption spectra of substitutional Co 2+ ions in Mg x Cd 1– x Se alloys

Abstract

Optical absorption spectra of substitutional Co2+ ions in Mgx Cd1–x Se alloys were investigated in the composition region of 0.0 ≤ x ≤ 0.4 and in the wavelength region of 300 to 2500 nm at 4.8 K and 290 K. We observed several absorption bands in the wavelength regions corresponding to the 4A2(4F) → 4T1(4P) transition and the 4A2(4F) → 4T1(4F) transition of Co2+ at a tetrahedral Td point symmetry point in the host crystals, as well as unknown absorption bands. The several absorption bands were analyzed in the framework of the crystal-field theory along with the second-order spin-orbit coupling. The unknown absorption bands were assigned as due to phonon-assisted absorption bands. We also investigated the variations of the crystal-field parameter Dq and the Racah parameter B with composition x in the Mgx Cd1–x Se system. The results showed that the crystal-field parameter (Dq ) increases, on the other hand, the Racah parameter (B ) decreases with increasing composition x, which may be connected with an increase in the covalency of the metal-ligand bond with increasing composition x in the Mgx Cd1–x Se system. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)