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Halides

Erbium(III) fluoride is a pinkish powder that can be produced by reacting erbium(III) nitrate and ammonium fluoride. It can be used to make infrared light-transmitting materials and up-converting luminescent materials, and is an intermediate in the production of erbium metal prior to its reduction with calcium. Erbium(III) chloride is a violet compounds that can be formed by first heating erbium(III) oxide and ammonium chloride to produce the ammonium salt of the pentachloride (ErCl) then heating it in a vacuum at 350-400 °C. It forms crystals of the AlCl type, with monoclinic crystals and the point group C 2/m. Erbium(III) chloride hexahydrate also forms monoclinic crystals with the point group of P 2/ n (P 2/ c) - C. In this compound, erbium is octa-coordinated to form ions with the isolated Cl completing the structure.

Erbium(III) bromide is a violet solid. It is used, like other metal bromide compounds, in water treatment, chemical analysis and for certain crystal growth applications. Erbium(III) iodide is a slightly pink compound that is insoluble in water. It can be prepared by directly reacting erbium with iodine.