Optical Absorption of Cobalt in Manganese Fluoride

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 ⁴T_1g(F)→⁴T_2g(F), ⁴A_2g(F), and ⁴T_1g(P) transitions of substitutional Co²⁺, 3d⁷ ions. The D_2h symmetry provided by the rutile structure of the MnF₂ lattice produced marked orthorhombic splitting of about 3000 cm⁻¹ in the ⁴T_1g(P) band. Several weak spin‐forbidden bands are also seen. The observed anisotropy indicates that the ⁴T_2g(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.