Luminescence

Luminescence is light emitted by a substance through processes other than heating, including chemical reactions, electrical excitation, and absorbed radiation.

Photoluminescence: Light emission caused by a substance absorbing photons and subsequently releasing energy as photons. It is the broad family of emissions triggered by absorbed light.
Electronic excited state: A state in which an atom or molecule has more electronic energy than its ground state. Luminescence begins when excitation places a system above its ground state.
Light-emitting diode: A semiconductor device that emits light when electric current passes through it. It converts electrical energy into light through electroluminescence.
Incandescence: Light emission from an object because its high temperature causes thermal radiation. Unlike luminescence, its light is produced by heating the emitting body.
Eilhard Wiedemann: A German physicist who introduced the term “luminescence” in the nineteenth century. He named emissions that were not explained by temperature alone.
Fluorescence: Photoluminescence that typically stops almost immediately after excitation ends. It is a fast, common pathway from optical excitation to emitted light.
Ground state: The lowest-energy state available to an atom, molecule, or other physical system. Emission commonly returns an excited system toward this lower-energy state.
Fluorescence microscopy: Microscopy that uses fluorescent labels or materials to form images from emitted light. Fluorescent emission makes selected structures visible against a dim background.
Black-body radiation: Electromagnetic radiation emitted by an ideal body in thermal equilibrium, determined by its temperature. It provides the standard example of light emission governed by heat.
Robert Boyle: An Anglo-Irish natural philosopher whose experiments included the light produced by phosphorus. His observations helped establish that some substances emit light without being heated.

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