Site occupancy and spectroscopic properties of Mn⁴⁺ in double perovskites, La₂MgGeO₆

The spectroscopic properties of Mn⁴⁺ (3 d³)in the La₂MgGeO₆ double perovskite is the subject of this investigation. The optical data have been used to perform detailed crystal field calculation of the Mn⁴⁺ energy level scheme. In La₂GeMgO₆, the Mn⁴⁺ can occupy either the octahedral Mg²⁺ or the Ge⁴⁺ sites. To address the question of site occupation, the Mn⁴⁺ energy levels were calculated when the ion substitutes for the Mg²⁺ and Ge⁴⁺ sites of the double perovskite lattice. An unambiguous decision on the site occupation cannot be reached based on our calculations. A comparative study of the variations in the energy of the ²E_g→⁴A_2g emission transition in a series of materials with the double perovskite structure is presented. The energy of the ²E_g→⁴A_2g emission transition tends to increase with increasing distortion of the octahedral O–Mn–O bond angle from the ideal 90°.