Optical spectra of Mn⁴⁺ in double perovskites Ba₂LnNbO₆ (Ln= La, Gd, Y)

This paper presents a comparative study of the optical properties of Mn⁴⁺ ion in three double perovskite compounds with the formula Ba₂LnNbO₆, where Ln = La, Gd, Y. The energy levels of the Mn⁴⁺ ion 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 Mn⁴⁺ energy levels are in good agreement with the experimental spectra. We also show that the energy of the ²E→A₂ emission transition (zero-phonon R-line) is dependent on the degree to which the O–M–O bond angle is reduced from the ideal 90° of the MnO₆ octahedron. Comments are made on the intensity of the R-line in the three double perovskites.