The nephelauxetic function he: A tool to locate the emission of Mn4+ in oxides and fluorides

A semi-empirical method is introduced to estimate the emission energy of the Mn⁴⁺ ion in fluorides and oxides without using spectroscopic data as inputs. The method is based on the calculation of the nephelauxetic function he at the octahedral crystal sites occupied by the Mn⁴⁺ cations in the considered host lattices. Only structural data are required for this calculation. The model reproduces the experimental emission energy of Mn⁴⁺ in 51 tested fluorides and 101 tested oxides within ±300 cm⁻¹ in 98% of the fluorides and within ±500 cm⁻¹ in 85% of the oxides. The accuracy is lowered as the he value, i. e. the covalency of the Mn–O bonding, is raised.