Luminescence of Mn4+ in the orthorhombic perovskites, AZrO3 (A=Ca, Sr)

Abstract The spectroscopic properties of the Mn4+ (3d3) ion in the orthorhombic perovskites ABO3 (A = Ca, Sr; B Zr4+) is the subject of this investigation. The optical properties of the Mn4+ ion in CaZrO3 is sensitive to oxygen stoichiometry. Comparison with the reported optical properties of oxygen-stoichiometric CaZrO3:Mn4+ obtained by synthesizing in oxygen atmosphere indicates that the air sintered sample represents Mn4+ luminescence in an oxygen deficient perovskite lattice. The luminescence of SrZrO3:Mn4+ suggests that this perovskite is less prone to the formation of oxygen vacancies. The difference between the energies of the zero-phonon line (2E→4A2 transition; R-line) in CaZrO3 and SrZrO3 is related to the deviation of the octahedral O–Mn–O bond angle from the ideal 90° value. Comparison with isostructural perovskites ASnO3 (A = Ca, Sr) shows that the energy of the 2E level depends on the covalent character of B–O bonding. The stronger covalence of Zr4+ 4d0- O2− 2p bonding compared to that of Sn4+ 4d10 - O2− 2p bonding is responsible for the higher energy position of the Mn4+ 2E level in the zirconate perovskite. Mulliken population analysis and bond order calculations are made to understand the nature of chemical bonding in the perovskites ABO3 (A = Ca, Sr; B= Zr4+, Sn4+).