Uses of Lanthanoids

Lanthanoids and their compounds find a range of important practical applications, many of which exploit either their characteristic magnetic and optical (f-f transition) properties or the ease with which mixtures of lanthanoids can be used together without separation.

Mischmetal and alloys. A mixture of lanthanoid metals -- roughly cerium and lanthanum together with smaller amounts of the other lanthanoids, along with a small amount of iron and traces of other elements -- known as mischmetal, is a pyrophoric alloy (it sparks readily when scratched or struck) used to make the flint in cigarette lighters and gas lighters. Mischmetal is also alloyed with magnesium to produce lightweight, high-strength alloys used in jet-engine components, bullet and shell casings, and other applications where a combination of low density and mechanical strength at elevated temperature is required.

Catalysts. Mixed lanthanoid oxides are used as catalysts in the petroleum industry, particularly in the catalytic cracking of crude oil fractions into more valuable, lower-molecular-weight hydrocarbons; lanthanoid-containing catalysts are also used in some catalytic converters for exhaust-gas treatment.

Glass and abrasive uses. Cerium(IV) oxide, $\text{CeO}_2$, is used extensively as a polishing agent for glass, optical lenses and mirrors, on account of its unusually effective, gentle abrasive action on glass surfaces.

Phosphors and display technology. Certain lanthanoid ions, particularly those of europium and terbium, are used as phosphors -- compounds that emit sharp, characteristically coloured light when excited -- in colour television and computer-display screens, fluorescent lighting tubes, and light-emitting diodes (LEDs), taking advantage of the sharp, well-defined f-f electronic transitions characteristic of lanthanoid ions. …