[en] A series of Al"3"+ -doped 3.5MgO·0.5MgF_2·GeO_2:Mn"4"+ red-emitting phosphors is synthesized by high temperature solid-state reaction. The broad excitation band at 300 nm–380 nm, resulting from the "4A_2 → "4T_1 transition of Mn"4"+, exhibits a blue shift with the increase of Al_2O_3 content. The observation of the decreased Mn"4"+O"2"− distance is explained by the crystal field theory. The temperature-dependent photoluminescence spectra with various amounts of Al_2O_3 content are comparatively measured and the calculation shows that the activation energy increases up to 0.41 eV at the Al_2O_3 content of 0.1 mol. The maximum phonon densities of state for these samples are calculated from Raman spectra and they are correlated with the thermal properties. (paper)