Neodymium(III) chloride or neodymium trichloride is a chemical compound of neodymium and chlorine with the formula NdCl₃. This anhydrous compound is a mauve-colored solid that rapidly absorbs water on exposure to air to form a purple-colored hexahydrate, NdCl₃·6H₂O. Neodymium(III) chloride is produced from minerals monazite and bastnäsite using a complex multistage extraction process. The chloride has several important applications as an intermediate chemical for production of neodymium metal and neodymium-based lasers and optical fibers. Other applications include a catalyst in organic synthesis and in decomposition of waste water contamination, corrosion protection of aluminium and its alloys, and fluorescent labeling of organic molecules (DNA).

NdCl₃ is a mauve colored hygroscopic solid whose color changes to purple upon absorption of atmospheric water. The resulting hydrate, like many other neodymium salts, has the interesting property that it appears different colors under fluorescent light- In the chloride's case, light yellow (see picture). The color difference is likely due to the charge transfer converting the Nd³⁺ ions into the Nd²⁺ state; the orange absorption band of Nd³⁺ decreases and the green Nd²⁺ absorption increases producing the yellowish color.

The anhydrous NdCl₃ features Nd in a nine-coordinate tricapped trigonal prismatic geometry and crystallizes with the UCl₃ structure. This hexagonal structure is common for many halogenated lanthanides and actinides such as LaCl₃, LaBr₃, SmCl₃, PrCl₃, EuCl₃, CeCl₃, CeBr₃, GdCl₃, AmCl₃ and TbCl₃ but not for YbCl₃ and LuCl₃.

...
Wikipedia