n.
Emission of electromagnetic radiation , usually visible light, caused by excitation of atoms in a material, which then reemit almost immediately (within about 10 -8 seconds).
The initial excitation is usually caused by absorption of energy from incident radiation or particles, such as X rays or electrons. Because re-emission occurs so quickly, the fluorescence ceases as soon as the exciting source is removed, unlike phosphorescence , which persists as an afterglow. A fluorescent lightbulb is coated on the inside with a powder and contains a gas; electricity causes the gas to emit ultraviolet radiation, which then stimulates the tube coating to emit light. The pixels of a television or computer screen fluoresce when electrons from an electron gun strike them. Fluorescence is often used to analyze molecules, and the addition of a fluorescing agent with emissions in the blue region of the spectrum to detergents causes fabrics to appear whiter in sunlight. X-ray fluorescence is used to analyze minerals.