Promethium(III) chloride is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

promethium Promethium is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of onl ...

and

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...

PmCl₃. It is an ionic, water soluble, crystalline salt that glows in the dark with a pale blue or green light due to promethium's intense radioactivity.

Applications

Promethium(III) chloride (with ¹⁴⁷Pm) has been used to generate long-lasting glow in signal lights and buttons. This application relied on the unstable nature of promethium, which emitted beta radiation (electrons) with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

of several years. The electrons were absorbed by a

phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or vi ...

, generating visible glow. Unlike many other radioactive nuclides, promethium-147 does not emit alpha particles that would degrade the phosphor.

References

Promethium compounds Chlorides Lanthanide halides {{inorganic-compound-stub