Optical properties of Mn4+-activated Na2SnF6 and Cs2SnF6 red phosphors

Alkaline hexafluorostantanate red phosphors Na2SnF6:Mn4+ and Cs2SnF6:Mn4+ are synthesized by chemical reaction in HF/NaMnO4 (CsMnO4)/H2O2/H2O mixed solutions immersed with tin metal. X-ray diffraction patterns suggest that the synthesized phosphors have a tetragonal symmetry with the space group D4h14 (Na2SnF6:Mn4+) and a trigonal symmetry with the space group D3d3 (Cs2SnF6:Mn4+). Photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and the Raman scattering techniques are used to investigate the optical properties of the phosphors. The Franck–Condon analysis of the PLE data yields the Mn4+-related optical transitions to occur at ∼2.39 and ∼2.38eV (4A2g→4T2g) and at ∼2.83 and ∼2.76eV (4A2g→4T1g) for Na2SnF6:Mn4+ and Cs2SnF6:Mn4+, respectively. The crystal field parameters (Dq) of the Mn4+ ions in the Na2SnF6 and Cs2SnF6 hosts are determined to be ∼1930 and ∼1920cm−1, respectively. Temperature-dependent PL measurements are performed from 20 to 440K in steps of 10K, and the obtained results are interpreted by taking into account the Bose–Einstein occupation factor. Comprehensive discussion is given on the phosphorescent properties of a family of Mn4+-activated alkaline hexafluoride salts.