Ab initio and crystal field studies of the Mn ⁴-doped Ba ₂LaNbO ₆ double-perovskite

A detailed study using the ab initio DFT-based calculations of the electronic and optical properties of pure and Mn ⁴ doped Ba ₂LaNbO ₆ is presented in this paper. Comparison of the calculated electronic bands structure, density of states diagrams, and dielectric functions for the pure and doped crystal reveals the changes induced by the Mn ⁴ impurity ions. In addition, the energy levels of the Mn ⁴ ion in the ordered perovskite Ba ₂LaNbO ₆ are calculated by the exchange charge model (ECM) of crystal field theory and compared with the experimental data that has been presented in the literature. The calculated Mn ⁴ energy levels are in good agreement with the experimental spectra. Additionally, the excitation band shapes of the ⁴A _2g( ⁴F) ⁴T _2g( ⁴F) and ⁴A _2g( ⁴F) ⁴T _1g( ⁴F) transitions are modeled to estimate the zero-phonon lines (ZPL) positions and the effective number of phonons, which are involved in the corresponding excitation transition. The results of our calculations yield the crystal field parameter of Dq=1780 cm ^-1 and Racah parameters B=670 and C=3290 cm ^-1, with C/B=4.9 for the Mn ⁴ ion in the double-perovskite Ba ₂LaNbO ₆.