Nanocrystalline BaFCl: Sm3+ is an efficient photoluminescent X-ray storage phosphor which is based on the reduction of Sm3+ to Sm2+ upon exposure to ionizing radiation. We have characterized this storage phosphor by synchrotron X-ray powder diffraction and scanning electron microscope, and have investigated it for its suitability in dosimetry and imaging. Sm2+ ions generated by X-rays in nanocrystalline and microcrystalline BaFCl: Sm3+ have been studied by spectral hole-burning to gain a better understanding of the storage mechanism. By applying 19 mW/cm2 of gating light in the hole-burning process, a gating efficiency of 5.5 is achieved for nanocrystalline BaFCl: Sm2+. The microcrystalline BaFCl: Sm2+ obtained by a high-temperature method has higher efficiencies both in self- and photon-gated hole-burning.