Electronic structure of the copper(II) ion doped in cubic KZnF3

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Abstract
The absorption and magnetic circular dichroism spectra of 1%–3% copper(II) doped into the cubic perovskite host KZnF3 are measured over the temperature range 1.8–300 K. Sharp magnetic dipole allowed transitions 2Eg(Γ8)→2T2g(Γ7,Γ8) are observed together with accompanying vibrational fine structure. The spectra are interpreted on the basis of a tetragonally elongated CuF4−6 ground state geometry which arises from strong Jahn–Teller coupling. This results in a statistical distribution of three equivalent elongations which can undergo reorientation on the electron paramagnetic resonance time scale. The Jahn–Teller coupling within the 2T2g multiplet is partially quenched by spin–orbit coupling and the lowest Kramers doublet Γ7 has an octahedral geometry, while the higher lying Γ8 state has a small tetragonal distortion. This system presents an excellent opportunity to study the spectroscopy of the copper(II) ion in a cubic environment.