Fluorescence

Fluorescence is one of two kinds of <a href="/facts/Photoluminescence/L1u2PJIa">photoluminescence</a>, the emission of <a href="/facts/Light/jeofpMn4">light</a> by a substance that has absorbed light or other <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">electromagnetic radiation</a>. When exposed to <a href="/facts/Ultraviolet/kncBUqn5">ultraviolet</a> radiation, many substances will glow (fluoresce) with colored visible light. The color of the light emitted depends on the chemical composition of the substance. Fluorescent materials generally cease to glow nearly immediately when the radiation source stops. This distinguishes them from the other type of light emission, <a href="/facts/Phosphorescence/WshJFsKV">phosphorescence</a>. Phosphorescent materials continue to emit light for some time after the radiation stops.
This difference in timing is a result of quantum spin effects.
Fluorescence occurs when a <a href="/facts/Photon/mFNhAEzA">photon</a> from incoming radiation is absorbed by a <a href="/facts/Molecule/N9ljSfFq">molecule</a>, exciting it to a higher <a href="/facts/Energy_level/66x51Khc">energy level</a>, followed by the emission of light as the molecule returns to a lower energy state. The emitted light may have a longer <a href="/facts/Wavelength/kcJU0ymz">wavelength</a> and, therefore, a lower <a href="/facts/Photon/mFNhAEzA">photon</a> <a href="/facts/Energy/wd8PrQM7">energy</a> than the absorbed radiation. For example, the absorbed radiation could be in the <a href="/facts/Ultraviolet/kncBUqn5">ultraviolet</a> region of the <a href="/facts/Electromagnetic_spectrum/24LARvFY">electromagnetic spectrum</a> (invisible to the human eye), while the emitted light is in the <a href="/facts/Visible_spectrum/frPBh8o5">visible region</a>. This gives the fluorescent substance a distinct <a href="/facts/Color/XDvW7ESP">color</a>, best seen when exposed to <a href="/facts/Blacklight/pAQ4hnUq">UV light</a>, making it appear to glow in the dark. However, any light with a shorter wavelength may cause a material to fluoresce at a longer wavelength. Fluorescent materials may also be excited by certain wavelengths of visible light, which can mask the glow, yet their colors may appear bright and intensified. Other fluorescent materials emit their light in the infrared or even the ultraviolet regions of the spectrum.
Fluorescence has many practical applications, including <a href="/facts/Mineralogy/MeIK9lx9">mineralogy</a>, <a href="/facts/Gemology/3bxqnE2b">gemology</a>, <a href="/facts/Medicine/2fnp90Je">medicine</a>, chemical sensors (<a href="/facts/Fluorescence_spectroscopy/mBcweHKk">fluorescence spectroscopy</a>), <a href="/facts/Fluorescent_labelling/vKVEgb0v">fluorescent labelling</a>, <a href="/facts/Dye/a1NSlcsG">dyes</a>, biological detectors, cosmic-ray detection, <a href="/facts/Vacuum_fluorescent_display/70BmkStl">vacuum fluorescent displays</a>, and <a href="/facts/Cathode-ray_tube/8NVGx5C7">cathode-ray tubes</a>. Its most common everyday application is in (<a href="/facts/Gas-discharge_lamp/SQPgULuM">gas-discharge</a>) <a href="/facts/Fluorescent_lamp/R8SlXCyg">fluorescent lamps</a> and <a href="/facts/LED_lamps/kMsxpkk9">LED lamps</a>, where fluorescent coatings convert UV or blue light into longer wavelengths, resulting in <a href="/facts/White/L2qjm4G0">white light</a>, which can appear indistinguishable from that of the traditional but energy-inefficient <a href="/facts/Incandescent_lamp/31frjg0A">incandescent lamp</a>.
Fluorescence also occurs frequently in nature, appearing in some minerals and many biological forms across all kingdoms of life. The latter is often referred to as <a href="/facts/Biofluorescence/qsJVT2qP">biofluorescence</a>, indicating that the <a href="/facts/Fluorophore/wDWBmYhn">fluorophore</a> is part of or derived from a living organism (rather than an inorganic <a href="/facts/Dye/a1NSlcsG">dye</a> or <a href="/facts/Staining/jqGqWEE1">stain</a>). However, since fluorescence results from a specific chemical property that can often be synthesized artificially, it is generally sufficient to describe the substance itself as fluorescent.

Fluorescence open-in-new

Fluorescence