We present a method to describe the temperature dependence of emission Mössbauer spectra showing slow spin-lattice relaxations of Fe3 +  in MgO single crystals, obtained after implantation of 57Mn at ISOLDE/CERN. The analysis is based on the Blume-Tjon model for the line-shape of relaxing paramagnetic sextets with the spin relaxation rate, τ  − 1 as a parameter. The temperature dependent spin relaxation rate of Fe3 +  in MgO is found to increase to ~108 s − 1 at 647 K by assuming a relaxation rate of τ  − 1 < 106 s − 1 at 77 K. The results are in accordance with those obtained by electron paramagnetic resonance spectroscopy demonstrating the possibility of retrieving spin-lattice relaxation rates of dilute Fe3 +  from emission Mössbauer spectroscopy of Mn/Fe-implanted oxides.