The influence of calcium co-doping on the optical properties of the x-ray storage phosphor BaFBr: Eu2+, is determined by photo- stimulated luminescence techniques. It is found that the incorporation of calcium into the lattice results in a broadening of the photo- stimulation peak due to a calcium induced FA(Br, Ca2+)-centre with stimulation maxima at 540 and 680 nm. The optical cross-sections for the photo- stimulated process are determined by utilizing stimulation light with linearly increasing intensity. Furthermore, it is shown that the sensitivity for x-rays, i.e. the number of storage centres formed during x-ray exposure, increases up to a doping level of 1 mol% while it drops rapidly at higher calcium concentrations.