Optical Absorption of Cobalt in Manganese Fluoride

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Abstract
The polarized crystal spectra of cobalt‐doped MnF2 have been measured down to near 4.2°K. Three broad, anisotropic bands near 7200, 14 000, and 20 000 cm−1 are seen that are presumably due to the spin‐allowed 4T1g(F)→4T2g(F), 4A2g(F), and 4T1g(P) transitions of substitutional Co2+, 3d7 ions. The D2h symmetry provided by the rutile structure of the MnF2 lattice produced marked orthorhombic splitting of about 3000 cm−1 in the 4T1g(P) band. Several weak spin‐forbidden bands are also seen. The observed anisotropy indicates that the 4T2g(F) band is largely magnetic dipole while the other two are electric dipole. These latter parity‐forbidden transitions are aided by coupling with odd lattice vibrations. Application of the appropriate selection rules allows tentative identification of several of the states involved.