Lutetium, atomic no. 71, symbol Lu, weight at 174.97, is the last member of the rare earth series. Unlike most rare earths it lacks a magnetic moment. It also has the smallest metallic radius of any rare earth. It is perhaps the least naturally abundant of the lanthanides.
It is the ideal host for x-ray phosphors because it produces the densest known white material, lutetium tantalate (LuTaO4).
It is utilized as a dopant in matching lattice parameters of certain substrate garnet crystals, such as indium-gallium-garnet (IGG) crystals due its lack of a magnetic moment.