Dopant

A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance (in very low concentrations) in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that were in the crystal lattice of the material. These materials are very commonly either crystals of a semiconductor (silicon, germanium, etc.), for use in solid-state electronics; or else transparent crystals that are used to make lasers of various types. However, noncrystalline substances such as glass can also be doped with impurities in order to make some lasers.