Luminescence of Mn4+ ions in CaTiO3 and MgTiO3 perovskites: Relationship of experimental spectroscopic data and crystal field calculations

Abstract

Herein, the synthesis, structural and crystal field analysis and optical spectroscopy of Mn4+ doped metal titanates ATiO3 (A = Ca, Mg) are presented. Materials of desired phase were prepared by molten salt assisted sol-gel method in the powder form. Crystallographic data of samples were obtained by refinement of X-ray diffraction measurements. From experimental excitation and emission spectra and structural data, crystal field parameters and energy levels of Mn4+ in CaTiO3 and MgTiO3 were calculated by the exchange charge model of crystal-field theory. It is found that crystalline field strength is lower (Dq = 1831 cm−1) in the rhombohedral Ilmenite MgTiO3 structure due to the relatively longer average Mn4+O2− bond distance (2.059 Å), and higher (Dq = 2017 cm−1) in orthorhombic CaTiO3 which possess shorter average Mn4+O2− bond distance (1.956 Å). Spectral positions of the Mn4+2Eg → 4A2g transition maxima is 709 nm in MgTiO3 and 717 nm in CaTiO3 respectively in good agreement with calculated values.