isotopes Sm, Nd, and Nd allows determination of age and origin of rocks and meteorites in samarium–neodymium dating. Both elements are lanthanides and are very similar physically and chemically. Thus, Sm–Nd dating is either insensitive to partitioning of the marker elements during various geologic processes, or such partitioning can well be understood and modeled from the ionic radii of said elements. Sm ion is a potential activator for use in warm-white light emitting diodes. It offers high luminous efficacy due to the narrow emission bands; but the generally low quantum efficiency and too little absorption in the UV-A to blue spectral region hinders commercial application. In recent years it has been shown that nanocrystalline BaFCl:Sm as prepared by co-precipitation can serve as a very efficient x-ray storage phosphor. The co-precipitation leads to nanocrystallites of the order of 100-200 nm in size and their sensitivity as x-ray storage phosphors is increased an astounding ∼500,000 times because of the specific arrangements and density of defect centers in comparison with microcrystalline samples prepared by sintering at high temperature. The mechanism is based on reduction of Sm to Sm by trapping electrons that are created upon exposure to ionizing radiation in the BaFCl host. The D- F f-f luminescence lines can be very efficiently excited via the parity allowed 4f →4f 5d transition at ~417 nm. The latter wavelength is ideal for efficient excitation by blue-violet laser diodes as the transition is electric dipole allowed and thus relatively intense (400 L/(mol⋅cm)). The phosphor has potential applications in personal dosimetry, dosimetry and imaging in radiotherapy, and medical imaging. Samarium is used for ionosphere testing. A rocket spreads it as a red vapor at high altitude, and researchers tests how the atmosphere disperses it and how it impacts radio transmissions. Biological role and precautions Samarium salts stimulate metabolism, but it is unclear whether this is from samarium or other lanthanides present with it. The total amount of samarium in adults is about 50 μg, mostly in liver and kidneys and with ~8 μg/L being dissolved in blood. Samarium is not absorbed by plants to a measurable concentration and so is normally not part of human diet. However, a few plants and vegetables may contain up to 1 part per million of samarium. Insoluble salts of samarium are non-toxic and the soluble ones are only slightly toxic. When ingested, only ~0.05% of samarium salts is absorbed into