Phosphor is a substance that absorbs certain types of energy and gives off part of that energy as visible light. The energy can be supplied by X rays, cathode rays, ultraviolet radiations, or alpha particles from radioactive substances. If luminescence stops immediately after the energy supply is removed, the material is said to be fluorescent. If the light continues for some time, the material is phosphorescent. Phosphors are used in television tubes and other devices.
