Forbidden Mechanism - in Solid-state Physics

In Solid-state Physics

Forbidden transitions in rare earth atoms such as erbium and neodymium make them useful as dopants for solid-state lasing media. In such media the atoms are held in a matrix which keeps them from de-exciting by collision, and the long half life of their excited states makes them easy to "optically pump" to create a large population of excited atoms. Neodymium doped glass derives its unusual coloration from "forbidden" f-f transitions within the neodymium atom, and is used in extremely high power solid state lasers.