| http://www.w3.org/ns/prov#value | - The composition is of the formula MCl3, wherein M is at least one rare earth element from lanthanum, cerium, neodymium, praseodymium, dysprosium, samarium, yttrium, gadolinium, erbium, ytterbium, holmium, terbium, europium, thulium, lutetium, or mixtures thereof, with the proviso that, when cerium is present, at least one more rare earth element other than cerium is also present.
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