Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, ductile, and soft enough to be cut with a knife. Terbium is highly reactive. It should be stored in a container filled with inert gas or a vacuum container. Terbium Metal is the important additive for NdFeB permanent magnets to raise the Curie temperature and improve temperature coefficiency. Terbium is primarily used in phosphors, particularly in fluorescent lamps and as the high intensity green emitter used in projection televisions.