Phosphorescence

Phosphorescence, light produced by certain substances after the absorption of certain forms of energy, especially radiant energy. The light is produced when the electrons of the substance, excited by the radiation, drop back to lower energy levels. Phosphorescence is similar to fluorescence except that fluorescence occurs while the substance is subject to radiation, whereas phosphorescence continues even after the radiation has stopped. Natural forms of phosphorescence occur in gems and minerals. Some insects, such as fireflies, exhibit it too. Scientists use phosphorescent substances to track and examine body systems with X-rays. Manufacturers use phosphorescence in clock faces, computer monitors, and other products.

See also: Fluorescence; Luminescence.