Luminescence

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Luminescence is the emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a substance as a result of heating.

Types of Luminescence

Luminescence can be classified into several types based on the mechanism of excitation:

• Chemiluminescence: Light produced as a result of a chemical reaction.
• Bioluminescence: Light produced by living organisms, such as fireflies and certain types of jellyfish.
• Electroluminescence: Light produced by an electric current passed through a substance.
• Photoluminescence: Light produced by the absorption of photons. This can be further divided into:

 * Fluorescence: Immediate emission of light.
 * Phosphorescence: Delayed emission of light.

• Radioluminescence: Light produced by the bombardment of ionizing radiation.
• Triboluminescence: Light produced by mechanical action, such as friction or breaking of crystals.
• Thermoluminescence: Light produced by heating a substance.

Applications

Luminescence has a wide range of applications in various fields:

• Medical imaging: Used in techniques such as bioluminescence imaging to study biological processes.
• Forensic science: Utilized in crime scene investigations to detect substances that are not visible to the naked eye.
• Display technology: Employed in LEDs and OLEDs for screens and lighting.
• Chemical analysis: Used in chemiluminescence assays to detect the presence of specific chemicals.

Mechanism

The mechanism of luminescence involves the excitation of electrons to a higher energy state. When these electrons return to their ground state, they release energy in the form of photons, which is observed as light. The specific wavelength (color) of the emitted light depends on the energy difference between the excited state and the ground state.

History

The study of luminescence dates back to ancient times, with early observations recorded by Pliny the Elder and Aristotle. The term "luminescence" was coined in the late 19th century by the German physicist Eilhard Wiedemann.

See Also

• Fluorescence
• Phosphorescence
• Bioluminescence
• Chemiluminescence
• Electroluminescence
• Radioluminescence
• Triboluminescence
• Thermoluminescence

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