On the Mn⁴⁺ R-line Intensity and energy in the perovskite layer of SrLaAlO₄ and Sr₂TiO₄: A comparative study with LaAlO₃ and SrTiO₃

The Ruddlesden-Popper (RP) phases of SrLaAlO₄ and Sr₂TiO₄ crystallize in the tetragonal A₂BX₄ structure that consists of an intergrowth of rocksalt (AX) and perovskite (ABX₃) layers. In this article, the spectroscopic properties of Mn⁴⁺ embedded in the perovskite layer of SrLaAlO₄ and Sr₂TiO₄ are compared with those in the perovskites, LaAlO₃ and SrTiO₃. For both RP phases, we find that energy of the zero-phonon line (ZPL; R-line) is essentially the same as in the corresponding perovskites. Despite the presence of inversion symmetry about the Mn⁴⁺ ion, the R-line is intense in the RP compounds while they appear with weak intensity in the emission spectrum of the corresponding perovskites. In SrLaAlO₄ this is attributed to the removal of inversion symmetry by Al³⁺ vacancy and to the random distribution of Sr²⁺ and La³⁺ cations. In Sr₂TiO₄, the removal of inversion symmetry is hypothesized to occur via the off-center displacement of the Mn⁴⁺ ion.