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

Abstract

The spectroscopic properties of the Mn 4+ (3 d 3 ) ion in the orthorhombic perovskites A B O 3 (A = Ca, Sr; B Zr 4+ ) is the subject of this investigation. The optical properties of the Mn 4+ ion in CaZrO 3 is sensitive to oxygen stoichiometry. Comparison with the reported optical properties of oxygen-stoichiometric CaZrO 3 :Mn 4+ obtained by synthesizing in oxygen atmosphere indicates that the air sintered sample represents Mn 4+ luminescence in an oxygen deficient perovskite lattice. The luminescence of SrZrO 3 :Mn 4+ suggests that this perovskite is less prone to the formation of oxygen vacancies. The difference between the energies of the zero-phonon line ( 2 E→ 4 A 2 transition; R-line) in CaZrO 3 and SrZrO 3 is related to the deviation of the octahedral O–Mn–O bond angle from the ideal 90° value. Comparison with isostructural perovskites ASnO 3 (A = Ca, Sr) shows that the energy of the 2 E level depends on the covalent character of B –O bonding. The stronger covalence of Zr 4+ 4d 0 - O 2− 2p bonding compared to that of Sn 4+ 4d 10 - O 2− 2p bonding is responsible for the higher energy position of the Mn 4+ 2 E level in the zirconate perovskite. Mulliken population analysis and bond order calculations are made to understand the nature of chemical bonding in the perovskites A B O 3 (A = Ca, Sr; B = Zr 4+ , Sn 4+ ). • Luminescence of Mn 4+ in perovskites AZrO 3 are discussed. • Comparative study with Mn 4+ luminescence in perovskite ASnO 3 is provided. • Influence of covalent bonding on R-line energy is discussed. • Calculations of the Mulliken charges are used to interpret optical data.