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Fluorescence - definition & possibilities

  1. Dec 7, 2011 #1
    Is the term "fluorescence" limited to emission of visible light? (If the emitted light is IR, would this not be fluorescence?)
    In many demonstrations, UV light is absorbed and visible light is emitted, but is absorption of UV an essential feature of fluorescence? Or could it also be a visible-to-visible change like blue light (higher-energy visible) absorbed, some of this EM energy converted into lower-energy EM or other forms (heat,...), and then red light (lower-energy visible) emitted?
    Last edited: Dec 7, 2011
  2. jcsd
  3. Dec 7, 2011 #2


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  4. Dec 7, 2011 #3
    Thanks, Nascent, for the response and the link, which says "[gamma?] rays, x-rays, uv, visible light and ir radiations may all stimulate fluorescence." If IR absorption can stimulate, obviously the emissions cannot be limited to visible or higher.
    At least according to Biology Online. But does use of the term vary from one area to another, so in some fields of science there are more restrictions on what is and isn't called fluorescence? gf
  5. Dec 10, 2011 #4
    "As long as electromagnetic radiation continues to bombard the substance, electrons in the fluorescent material become excited but return very quickly to lower energy, giving off light, always of the same frequency." (from http://www.thefreedictionary.com/fluorescence )
    Is fluorescence emission always limited to one energy, not a range of energies, as stated here? (even if the material absorbs over a range) Or is this description too narrow?
    Also, I think "fluorescence" is limited to transitions between electronic energy levels, and there is no connection between fluorescence and a generalized blackbody radiation (like pavement absorbing high-energy sunlight, then emitting lower-energy IR over a range of wavelengths) even though in both cases higher-energy EM is absorbed and lower-energy EM is emitted. Is this correct? gf
  6. Dec 10, 2011 #5

    Andy Resnick

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    The term 'fluorescence' can be applied to the whole optical spectrum, AFAIK- it only refers to the mechanism of absorption and emission. Fluorescence also is related to lasing. I'm not sure if fluorescence and phosphorescence are considered related: one refers to 'allowed' transitions, while the other uses 'forbidden' transitions.
  7. Dec 10, 2011 #6
    Thanks for a confirmation of what seems to be the common use of this term, Andy. I've been web-searching more since posting, and everyone seems to agree with you, and Nascent,
    http://www.maxmax.com/aIRInks.htm says "Fluorescence can occur at any point of the electromagnetic spectrum. ... A material might absorb ultraviolet light and emit visible light, or absorb visible and emit infrared, or absorb near infrared and emit far infrared.
    I think fluorescence (quick emission) & phosphorescence (delayed emission due to "forbidden" transitions, as you say) are similar, both involving transitions between electronic energy levels, while blackbody radiation is different. This is explained (with Andy helping) in another PF-thread, https://www.physicsforums.com/showthread.php?t=382420
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