Why does it "hilite"?
November 22, 2006 12:41 PM   Subscribe

Can anyone tell me what gives fluorescent markers their... fluorescence?

Gorey chemical details preferred.
posted by sunshinesky to Science & Nature (13 answers total) 1 user marked this as a favorite
 
I think the wikipedia can: Fluorescence, Stokes Shift.
posted by metaculpa at 12:56 PM on November 22, 2006


I'm really more of a biologist but here goes: They contain a chemical which absorbs light at a certain wavelength. This absorption excites a molecule of said chemical (I think by moving its electrons into higher energy orbitals around various atoms.) However, this excited state cannot be sustained and when the electrons inevitably move to their lower energy orbitals they emit a photon at a different wavelength than the excitation light.
posted by dendrite at 1:06 PM on November 22, 2006


Response by poster: I'd already checked wiki on fluorescence, but it didn't mention use in the markers themselves. It must be true though!

Thanks
posted by sunshinesky at 1:09 PM on November 22, 2006


According to some patents I searched through, hydroxypyrenetrisulfonic acid can be used as a flurophore.
posted by grouse at 1:46 PM on November 22, 2006


To speak the unspoken part of the above explanation - the higher wavelengths (that it is absorbing) are generally invisible to the human eye, while the lower wavelengths (that it is emitting) are visible, thus the highlighter appears to emit more light than the ambient light, and so is brighter than surrounding objects, even though it's just reflecting ambient at a different wavelength.
posted by -harlequin- at 2:58 PM on November 22, 2006


Chemistry may not have as much to do with this as your subjective response to a narrow frequency range. I'll assume you're not talking about true fluorescence here. These markers are "bright", but they won't emit light in the dark, right?

Color has three components. Hue (frequency range) Saturation (purity) and Lightness (B&W value).

White is an example of a color with lightness, but not saturation. It is a mixture of virtually all visible frequencies hitting your eyes at the same time. Think of it as an orchestra with all the instruments playing fairly loudly at the same time. Imagine a balanced sound, so you can't pick out the individual instruments with your ear.

Now have just the flute play as loudly as the orchestra did. You will need an amplifier. It will sound very shrill and loud to your ear, yet it is the same volume as the whole orchestra was, and that didn't sound bad. The reason is that you're putting all that volume into a narrow frequency range. It's like getting stepped on with a high-heeled shoe vs. a snowshoe. The relatively narrow frequency range of these markers makes them seem brighter than they are. Write something on a sheet of white paper and make a photocopy to see that.
posted by weapons-grade pandemonium at 3:00 PM on November 22, 2006


An interesting experiment: try writing something with a highlighter and then shining a blacklight on it. It'll light up much brighter than the surrounding paper, and in an entirely different color than the rest of the paper too.

I'll assume you're not talking about true fluorescence here. These markers are "bright", but they won't emit light in the dark, right?

I think you may be mixing up fluorescence with phosphorescence.
posted by Johnny Assay at 3:09 PM on November 22, 2006


-harlequin- writes "the higher wavelengths (that it is absorbing) are generally invisible to the human eye, while the lower wavelengths (that it is emitting) are visible"

"Longer" and "shorter" are probably better terms when discussing wavelength. In -harlequin-'s explanation here, I'd replace "higher" with "shorter" and "lower" with "longer". Of course, you could also say that fluorophores absorb photons of higher frequency and emit photons of lower frequency. I'd avoid talking about long and/or short photons and/or frequencies, though.

I'm sure that makes everything perfectly clear.

As for gory chemical details, I would guess that a lot of the dyes used in these markers are proprietary, and, as grouse suggests, patented. A search of a patent database for the word "highlighter" brings up some pretty gory details.
posted by mr_roboto at 3:38 PM on November 22, 2006


You know who else liked gory chemicals: Hiliter
posted by weapons-grade pandemonium at 6:11 PM on November 22, 2006 [2 favorites]


To speak the unspoken part of the above explanation - the higher wavelengths (that it is absorbing) are generally invisible to the human eye, while the lower wavelengths (that it is emitting) are visible, thus the highlighter appears to emit more light than the ambient light, and so is brighter than surrounding objects, even though it's just reflecting ambient at a different wavelength.

You must mean higher frequencies/lower frequencies, or shorter wavelengths/longer wavelengths, harlequin. And these markers aren't "brighter" than the surrounding objects, because they appear darker than a white sheet of paper in a photocopy.
posted by weapons-grade pandemonium at 6:26 PM on November 22, 2006


dendrite hit the nail exactly on the head.

While the light we see hitting the flourecent dye is in the visible spectrum, the dye is actually absorbing (and thus moving electrons with) both higher (Ultraviolet) and lower (Infrared) wavelenths. But when the electrons "come down" (return to their original orbitals) from their "high" (increased energy state), they give off that energy as photons of visible light, thus making flourescent objects seem brighter than they should be. This is also why flourescent objects seem to glow in the presence of black lights; even though the black light doesnt give off visible light, the energy from the light hitting the flourescent molecules is released as visible light.
posted by dantekgeek at 1:48 AM on November 23, 2006


crap, made the higher/lower instead of shorter/longer slip with wavelengths. disregard my sillyness.
posted by dantekgeek at 1:49 AM on November 23, 2006


these markers aren't "brighter" than the surrounding objects, because they appear darker than a white sheet of paper in a photocopy

This doesn't seem relevant - a photocopier lamp is not akin to full spectrum ambient light, nor is a photocopier sensitive to the same frequencies as human eyes. The point is that it is not brighter by way of reflecting more photons than the surrounds, but brighter by way of skewing the same amount of photons as the surrounds towards a spectra that the eye is more able to see.
posted by -harlequin- at 3:54 PM on November 23, 2006


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