The Mn4+ ion has the same d3 electron configuration as Cr3+, but is less stable and can transform to other valence states. Both ions are known to occupy several sites in garnet hosts, giving rise to rather complicated optical spectra and photo-induced phenomena. Here, the spectra of the transient, photo-induced absorption and the emission of Mn4+,:YAG are analyzed over a broad wavelength region (from 450 to 1200nm) and over a wide range of time scales (from ns to minutes). Very large amplitude and extremely broadband excited state absorption are observed. Additionally, a long lifetime, photo-induced species was detected that is likely formed via charge transfer. The demonstrated behavior of this material shows it has potential applications for optical limiting and optical storage.