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Luminescence is a spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment. [ 1 ] A luminescent object emits cold light in contrast to incandescence , where an object only emits light after heating. [ 2 ]
A corollary of Kasha's rule is the Vavilov rule, which states that the quantum yield of luminescence is generally independent of the excitation wavelength. [4] [7] This can be understood as a consequence of the tendency – implied by Kasha's rule – for molecules in upper states to relax to the lowest excited state non-radiatively.
It is one of many forms of luminescence (light emission) and is initiated by photoexcitation (i.e. photons that excite electrons to a higher energy level in an atom), hence the prefix photo-. [2] Following excitation, various relaxation processes typically occur in which other photons are re-radiated.
Chemiluminescence (also chemoluminescence) is the emission of light (luminescence) as the result of a chemical reaction, i.e. a chemical reaction results in a flash or glow of light. A standard example of chemiluminescence in the laboratory setting is the luminol test. Here, blood is indicated by luminescence upon contact with iron in hemoglobin.
Views of a liquid crystal display, both with electroluminescent backlight switched on (top) and switched off (bottom). Electroluminescence (EL) is an optical and electrical phenomenon, in which a material emits light in response to the passage of an electric current or to a strong electric field.
Candoluminescence is the light given off by certain materials at elevated temperatures (usually when exposed to a flame) that has an intensity at some wavelengths which can, through chemical action in flames, be higher than the blackbody emission expected from incandescence at the same temperature. [1]
Like in triboluminescence, if the charge separation results in a large enough electric potential, a discharge across the gap and through the bath gas between the interfaces can occur. The potential at which this occurs depends upon the dielectric properties of the bath gas.
Photoluminescence excitation (abbreviated PLE) is a specific type of photoluminescence and concerns the interaction between electromagnetic radiation and matter.It is used in spectroscopic measurements where the frequency of the excitation light is varied, and the luminescence is monitored at the typical emission frequency of the material being studied.