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Dexter (also known as Dexter exchange or collisional energy transfer, colloquially known as Dexter Energy Transfer) is another dynamic quenching mechanism. [12] Dexter electron transfer is a short-range phenomenon that falls off exponentially with distance (proportional to e −kR where k is a constant that depends on the inverse of the van der Waals radius of the atom [citation needed]) and ...
Negative luminescence is most readily observed in semiconductors.Incoming infrared radiation is absorbed in the material by the creation of an electron–hole pair.An electric field is used to remove the electrons and holes from the region before they have a chance to recombine and re-emit thermal radiation.
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 ]
This change is most pronounced when electron-donating and electron-withdrawing groups are placed at opposite ends of an aromatic ring system, [13] as this results in a large change in dipole moment when excited. When a fluorophore is excited, it generally has a larger dipole moment (μ E) than in the ground state (μ G). Absorption of a photon ...
Common examples include fluorescent lamps, organic dyes, and even fluorspar. Longer emitters, commonly referred to as glow-in-the-dark substances, ranged from one second to many hours, and this mechanism was called persistent phosphorescence or persistent luminescence, to distinguish it from the other two mechanisms. [11]: 1–25
A tea light-type candle, imaged with a luminance camera; false colors indicate luminance levels per the bar on the right (cd/m 2). Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. [1]
Whereas the term "fluorescence" tended to refer to luminescence that ceased immediately (by human-eye standards) when removed from excitation, "phosphorescence" referred to virtually any substance that glowed for appreciable periods in darkness, sometimes to include even chemiluminescence (which occasionally produced substantial amounts of heat).
The amount of luminescence is proportional to the original dose of radiation received. In thermoluminescence dating, this can be used to date buried objects that have been heated in the past, since the ionizing dose received from radioactive elements in the soil or from cosmic rays is proportional to age. This phenomenon has been applied in the ...