Chlorides

Erbium (III) chloride, is a violet solid with the formula ErCl₃. It is used in the preparation of erbium metal. It is also found as a pink crystalline hexahydrate. It has the interesting property that the pink colour is much more intense under the light from a fluorescent lamp.

Anhydrous erbium (III) chloride is formed from the hexahydrate by heating under a strongly chlorinating atmosphere, such as chlorine or hydrogen chloride; otherwise erbium oxide chloride, ErOCl, is formed. An alternative preparation is to react the readily available Er₂O₃ with excess NH₄Cl to make the intermediate salt (NH₄)₃ErCl₆ plus both ammonia and water. This salt is stable with respect to hydrolysis and can be thermally decomposed under vacuum to yield anhydrous erbium(III) chloride with loss of ammonia and gaseous HCl.

There are many applications of materials which contain rare-earth ions utilizing their forced electric dipole f–f transitions; for example, lasers and fiber amplifiers. Special attention has been paid to all-optical devices for use in highspeed and parallel processing. For example, the third-order nonlinear optical effect is used to obtain optical switching devices which might eventually be used in an optical computer.

Erbium chloride forms crystals of the AlCl₃ type, with monoclinic crystals and the point group C2/m. Erbium(III) chloride hexahydrate also forms monoclinic crystals with the point group of P2/n (P2/c) - C⁴_2h. The erbium is octa-coordinated to form [Er(H₂O)₆Cl₂]⁺ ions with the isolated Cl⁻ completing the structure.

Erbium compound materials, such as ErOOH and Er₂O₃, are recognized as one of the most important rare earth oxides for sensing applications in the lasers and optical amplifiers, due to intra Er³⁺ 4f shell transition from its first excited state (⁴I_3/2) to the ground state (⁴I_5/2). Recently, flaky rare earth oxide including Er₂O₃ is also used as additives on nickel electrodes and their effects on high temperature performance of nickel electrodes is also investigated. The result proved that flaky rare earth oxides increases the oxygen evolution potential and improves the reversibility of nickel electrode.