Efficient X-ray generation of relatively stable Sm2+ centers is observed in nanocrystalline Sm3+-activated BaFCl, as prepared by a one-step wet chemical reaction. The conversion efficiency is approximate to 50 000 times higher than that in microcrystalline BaFCl/Sm3+ prepared at 900 degrees C. The Sm2+ centers, and hence the radiation dose, can be directly monitored by the narrow photoexcited D-5(J)-F-7(J) f-f luminescence lines. The relatively high efficiency of Sm2+ generation appears to be directly linked to the particle size.