Fluorescence is the emission of electromagnetic radiation light by a substance that has absorbed radiation of a different wavelength. In most cases, absorption of light of a certain wavelength induces the emission of light with a larger wavelength (and lower energy). However, under conditions in which intense radiation is being absorbed, it is possible for one electron to absorb two photons (multiple photon absorption), which can lead to the emission of radiation having a smaller wavelength than the excitation source. The energy difference between the absorbed and emitted photons is due to thermal losses. Dissipation of vibrational energy occurs on a much greater time scale than fluorescent emission. The most striking examples of this phenomenon occur when the absorbed photon is in the ultraviolet region of the spectrum, and is thus invisible, and the emitted light is in the visible region. Practical applications of this effect are found in mineralogy, gemology, chemical sensors, fluorescent labelling, dyes, biological detectors etc. Newer applications of fluorescent compounds are being explored daily.
The term 'fluorescence' was coined by George Gabriel Stokes in his 1852 paper;[1] the name was suggested "to denote the general appearance of a solution of sulphate of quinine and similar media". (Phil. Trans. R. Soc. Lond. 1853 143, 385-396 [quote from page 387). The name itself was derived from the mineral fluorite (calcium difluoride), some examples of which contain traces of divalent europium, which serves as the fluorescent activator to provide a blue fluorescent emission. The fluorite which provoked the observation originally, and which remains one of the most outstanding examples of the phenomenon, originated from the Weardale region, of northern England.
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Drug Discovery & Development
These products, and a new filter-based Fluorescence Intensity cartridge, join a line of 14 previously released cartridges that can be exchanged in the ...
