Influence of Covalency on the Mn^{4+ 2}E_g→⁴A_2gEmission Energy in Crystals

In this paper we review the spectroscopic properties of the Mn4+ ion (3d3 electronic configuration) and establish a relationship between the energy of the 2Eg → 4A2g emission transition and the covalence of the "Mn4+-ligand" bonding. A new parameter (where (B, C (B0, C0) are the Racah parameters of the Mn4+ ions in a crystal (free state), respectively) was recently introduced that allows for establishing a linear relationship between β1 and the energy of the 2Eg level. This makes it possible to understand the large variation in the energy of the 2Eg → 4A2g emission transition that is frequently encountered in the spectroscopy of the Mn4+ ions in solids.