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 similar to 2.39 and similar to 2.35 eV ((4)A(2)-> T-4(2)) and at similar to 2.82 and similar to 2.79 eV ((4)A(2)-> T-4(1)) 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, v(1)-v(6), are determined from the PL and Raman scattering spectra of Cs2SiF6:Mn4(+) and Cs2GeF6:Mn4(+). (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3576124] All rights reserved.