A dopant, also called doping agent and dope,'s an impurity element added to a crystal lattice in low concentrations in order to alter the optical/electrical properties of the crystal. Doping with Yb, Er, Nd, Tm or Cr of optical single crystals, ceramics and glasses's used to make solid-state lasers; the elements mentioned are the most common dopants. In many optically-transparent hosts, such active centers may keep their excitation for a time on the order of milliseconds, and relax with stimulat… (More on Dopant)