Properties of Mn4+-Activated Hexafluorotitanate Phosphors

Alkali hexafluorotitanate red phosphors A(2)TiF(6):Mn4+ (A = K, Cs, and Na) are synthesized by chemical etching of TiO2 in aqueous hydrofluoric acid (HF)/alkali permanganate (AMnO(4))/alkali fluoride (AF) solutions. X-ray diffraction patterns suggest that the synthesized phosphors have a trigonal symmetry with the space groups D-3d(3) (K2TiF6:Mn4+ and Cs2TiF6:Mn4+) and D-3(2) (Na2TiF6:Mn4+). The luminescent properties of the phosphors are studied by photoluminescence (PL) analysis and PL excitation spectroscopy. Trigonal distortion splits the threefold degenerate nu(3), nu(4), and nu(6) vibronic emission lines. The Raman scattering of A(2)TiF(6):Mn4+ is also investigated using a triple monochromator at room temperature. The infrared- and Raman-active fundamental frequencies are determined and discussed from the viewpoint of crystal symmetry. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3530793] All rights reserved.