Luminescence. Luminescence is a spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment. A luminescent object emits cold light in contrast to incandescence, where an object only emits light after heating. Generally, the emission of light is due to the movement of electrons between different energy levels within an atom after excitation by external factors. However, the exact mechanism of light emission in vibrationally excited species is unknown. 

The dials, hands, scales, and signs of aviation and navigational instruments and markings are often coated with luminescent materials in a process known as luminising.

Types
 Ionoluminescence, a result of bombardment by fast ions
 Radioluminescence, a result of bombardment by ionizing radiation
 Electroluminescence, a result of an electric current passed through a substance
 Cathodoluminescence, a result of a luminescent material being struck by electrons
 Chemiluminescence, the emission of light as a result of a chemical reaction
 Bioluminescence, a result of biochemical reactions in a living organism
 Electrochemiluminescence, a result of an electrochemical reaction
 Lyoluminescence, a result of dissolving a solid (usually heavily irradiated) in a liquid solvent
 Candoluminescence, is light emitted by certain materials at elevated temperatures, which differs from the blackbody emission expected at the temperature in question.
 Mechanoluminescence, a result of a mechanical action on a solid
 Triboluminescence, generated when bonds in a material are broken when that material is scratched, crushed, or rubbed
 Fractoluminescence, generated when bonds in certain crystals are broken by fractures
 Piezoluminescence, produced by the action of pressure on certain solids
 Sonoluminescence, a result of imploding bubbles in a liquid when excited by sound
 Crystalloluminescence, produced during crystallization
 Thermoluminescence, the re-emission of absorbed energy when a substance is heated
 Cryoluminescence, the emission of light when an object is cooled (an example of this is wulfenite)
 Photoluminescence, a result of the absorption of photons
 Fluorescence, traditionally defined as the emission of light that ends immediately after the source of excitation is removed. As the definition does not fully describe the phenomenon, quantum mechanics is employed where it is defined as there is no change in spin multiplicity from the state of excitation to emission of light.
 Phosphorescence, traditionally defined as persistent emission of light after the end of excitation. As the definition does not fully describe the phenomenon, quantum mechanics is employed where it is defined as there is a change in spin multiplicity from the state of excitation to the emission of light.

Applications
 Light-emitting diodes (LEDs) emit light via electro-luminescence.
 Phosphors, materials that emit light when irradiated by higher-energy electromagnetic radiation or particle radiation
 Laser, and lamp industry
 Phosphor thermometry, measuring temperature using phosphorescence
 Thermoluminescence dating
 Thermoluminescent dosimeter
 Non-disruptive observation of processes within a cell.

Luminescence occurs in some minerals when they are exposed to low-powered sources of ultraviolet or infrared electromagnetic radiation (for example, portable UV lamps) at atmospheric pressure and atmospheric temperatures. This property of these minerals can be used during the process of mineral identification at rock outcrops in the field or in the laboratory.

History
The term luminescence was first introduced in 1888.

See also
 List of light sources
 Scientific American, "Luminous Paint" (historical aspects), 10-Dec-1881, pp.368
 High-visibility clothing

References

External links

 Fluorophores.org A database of luminescent dyes

 
Light sources
1880s neologisms