Optical Transitions and Internal Vibronic Frequencies of MnF ₆ ^{2 -} Ions in Cs₂SiF₆ and Cs₂GeF₆ Red Phosphors

Cs₂SiF₆:Mn₄₊ and Cs₂GeF₆:Mn₄₊ red phosphors are synthesized by chemically etching Si and Ge in aqueous HF/CsMnO₄ solutions. Photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and 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 ∼2.35 eV (₄A₂→₄T₂) and at ∼2.82 and ∼2.79 eV (₄A₂→₄T₁) for Cs₂SiF₆:Mn₄₊ and Cs₂GeF₆:Mn₄₊, respectively. Temperature-dependent PL measurements are performed from 20 to 450 K in increments of 10 K, and the obtained results are well interpreted by taking into account the Bose–Einstein occupation factor. A complete set of infrared and Raman active frequencies, ν ₁–ν ₆, are determined from the PL and Raman scattering spectra of Cs₂SiF₆:Mn₄₊ and Cs₂GeF₆:Mn₄₊.