Exchange Effects in the Electronic Absorption Spectrum of Mn(II) in Perovskite Fluorides

Abstract

The electronic absorption spectrum of Mn in cubic perovskite fluorides is strongly modified by exchange interaction. This has been shown from the temperature dependence and concentration dependence of the spectrum of Mn in KZnF₃ and the temperature dependence of the spectrum of KMnF₃. The electronic transitions of particular interest are the ones near 4000 and 3300 Å which have narrow line structure. This structure has been analyzed and the contribution to the intensity from single ions and pairs of ions (Mn–F–Mn) evaluated. Studies of the temperature dependence of the pair lines give a ground state J (JS_a·S_b) interaction) of between +3.0° and +3.5°K and it is about twice as large in the excited state. The absorption lines correspond to pure electronic transitions and the selection rule is ΔS=0. The anomalously intense bands in the spectrum of KMnF₃ are interpreted on the basis of pure electronic transitions involving more than one ion and the temperature shifts of the bands have been correlated with known magnetic and structural changes.