Fluorescence

There are solids that fluoresce and liquids that fluoresce too like Mr. Clean.

Is there such thing as a gas the fluoresces in green or blue? I was thinking about diluting highlighter ink in water and spraying it though a spray bottle. Be kinda messy though.

Well if there are any gases that fluoresce they must be pretty rare.

Krypton would probably fluoresce, but its expensive, maybe Xenon and Neon as well. Not sure how exactly they would react to the 405nm laser light though.

null said:

Krypton would probably fluoresce, but its expensive, maybe Xenon and Neon as well.  Not sure how exactly they would react to the 405nm laser light though.

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probably not at all... they are well known for the fact that they only react if you force them...

I'm not sure that there isn't gas that fluoresces. However, in a gas the atoms are much more spread out then with solids or liquids. This lowers the probability of collision of an atom and a photon resulting in the photon being absorbed. For each collision that occurs an electron must absorb the energy of the photon (which for a single electron must be exactly the energy difference between any two energy levels). The energy must not be too much as to free the electron from the atom completely (in a bulk material this isn't bad as the electron would move to the 'conduction band' of the bulk material). The electron must then fall to an energy level higher than the original level emitting a photon of lower energy (longer wavelength) than the incident photon. If the electron falls to the original level the emitted photon will be the same wavelength as the incident.

Now for every collision that satisfies these conditions for emitting longer wavelength photons, only 1 photon is emitted. So odds are unless you have a very dense gas (which would probably need to be under enough pressure which would make it turn into liquid) you would probably not see any measurable brightness in fluoresced light.

This is just my thinking through the issue and in no way is guaranteed to be correct.

If you did the highlighter spray, it wouldn't really be gas, just falling liquid particles. However... I would like to see what would happen if you put Mr. Clean in a fog machine. ;D

randomlugia said:

If you did the highlighter spray, it wouldn't really be gas, just falling liquid particles. However... I would like to see what would happen if you put Mr. Clean in a fog machine. ;D

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Haha that would be interesting to see. I guess that under the right circumstances maybe a gas could fluoresce. I'll ask my physics professor and see what he thinks.

randomlugia said:

If you did the highlighter spray, it wouldn't really be gas, just falling liquid particles. However... I would like to see what would happen if you put Mr. Clean in a fog machine. ;D

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Break the fog machine or intoxicate people in the room probably But might also result in creation of a black hole that would swallow the earth and solar system :

null said:

Krypton would probably fluoresce, but its expensive, maybe Xenon and Neon as well.  Not sure how exactly they would react to the 405nm laser light though.

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Krypton and xenon do not fluoresce. You can find them in flashlight bulbs for a couple of bucks. I tried it last night, and nothing happened.

However, there is at least one gas I know of that fluoresces, and that's mercury vapor. At least, I think that's what is fluorescing. Shine your laser on a fluorescent lightbulb (Hmm... wonder where that name came from...), and it will glow red.

-Mark

The mercury is not a vapor until it's heated by electrical current. When hot and exited, it puts out 365nm which excites the phosphors. Your BR is likely exciting some of those phosphors.

Flourescent lightbulbs do glow red with a blacklight. I tried with the long stick lights, and it glowed dark blue. Then with the small flourescent aquarium lights, which glowed a very bright sky blue.

For gasses the energy needed is too high for short wavelength light sources (i.e. blue-violet/UV) to induce fluorescence.  You need much much more energy to promote the gas atoms to a higher energy level to produce photons.  You can do it with a high voltage, just like what one would use with neon lights.  That's essentially fluorescing gases.

Hope that helps!

If 405nm cannot fluoresce gases, why then do fluorescent lights glow brightly when we shine our lasers on them?

-Mark

You're fluorescing the phosphor in the tube. The tube contains mercury, which is vaporized and ionized to form a plasma. The plasma emits at a low wavelength, which causes the phosphor inside the tube to fluoresce, and the combination of plasma emission and phosphor emission gives you the illusion/impression of white light.

Your laser excites the phosphor inside the light just like the light from the mercury vapor does, causing it to fluoresce.

Also, fluorescence is generally thought of as emission that is caused by incident light, or photoluminesence. At least for me and people I know, with plasma/gases ionized by a high voltage, I don't generally think of those as involving fluorescence. Those are just ionized gases, plasma. I typically think of plasma light emission as being much more like electroluminescence, and really having very little to do with photoluminescence.

Thank you!

-Mark

No problem.

The other thing I've been trying to wrap my head around and figure out if it's "fluorescence" or not is when a laser ionizes a gas, making it a plasma, and that plasma glows. I think it would be considered fluorescence, since it is just light supplying all the energy, there's no other energy input, but I had to think about what's happening inside for a second (an ionized gas is still VERY different from the materials that are generally thought of as "fluorescing").

But I think I have come to the conclusion that yes, gases can fluoresce, and that fluorescence can be caused by simple incident light. BUT, it has to be special circumstances. Here's an example of a real device that does what I'm thinking of: a very small point of air gets hit by a very high intensity burst from a laser. the gas at the focal point, where the energy density of the laser light is highest, can actually get ionized, and emit light when it does so. http://www.physorg.com/news11251.html Pretty cool device actually.

The same thing can also happen with very low wavelength laser, where the beam actually weakly ionizes gas throughout the beam path, you can see this with some lasers at least.