Visible Light Fluorescence

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  • #1
Awwtumn
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https://en.wikipedia.org/wiki/Fluorescence

You normally heard of Fluorescence coming from UV which make the objects glow.

fluorescence emission.JPG


But visible light can also cause fluorescence. When you hit a colorful sample with a 532nm laser, there is fluorescence in the visible spectrum (as seen in Raman spectra). So how do you differentiate between the Fluorescence of objects that glow with UV absorption and visible light fluorescence and to that of visible light absorption and fluorescence? Specifically, do all color visible objects fluoresce? Whenever I aimed the 532nm Raman on color objects (such as red paint on a tin can), all I got are fluorescence which overlaps the small Raman signals.

Is this related to the fact that all colorful objects use paint in form of dyes and dyes can fluoresce? Can you give some list of colorful objects that won't fluoresce in visible light (using 532nm laser) so I can test this using Raman?

Also does this mean in everyday objects, there is continuous fluorescence from the visible light absorption and emission that we just don't see or distinguish with our naked eyes?
 

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  • #2
DrClaude
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You normally heard of Fluorescence coming from UV which make the objects glow.
In the picture you posted, it says "UV/Visible absorption" :smile:
So how do you differentiate between the Fluorescence of objects that glow with UV absorption and visible light fluorescence and to that of visible light absorption and fluorescence?
There no distinction to be made.
Specifically, do all color visible objects fluoresce? Whenever I aimed the 532nm Raman on color objects (such as red paint on a tin can), all I got are fluorescence which overlaps the small Raman signals.
It is a question of which pathways are fastest. For most substances, I would guess that internal conversion to heat is the main decay process, so there ill not be much fluorescence. Shining a laser is an exceptional case.
Can you give some list of colorful objects that won't fluoresce in visible light (using 532nm laser) so I can test this using Raman?
Try and see what you get with metals and rocks.
Also does this mean in everyday objects, there is continuous fluorescence from the visible light absorption and emission that we just don't see or distinguish with our naked eyes?
As I said above, I don't think most substances fluoresce much under ordinary light.
 
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  • #3
phinds
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As I said above, I don't think most substances fluoresce much under ordinary light.
Most substances don't even fluoresce under UV
 
  • #4
tech99
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I know that the long persistence CRT screen phosphor type P7 fluoresces green in ordinary white light. Some objects such as white paper and clothing include a UV fluorescent dye to make them look whiter and I have used printer paper as a screen in demonstrations of UV. Some plastics contain fluorescent dyes, and of course we have dyes intended for the purpose, such as fluorescein. I don't think most objects fluoresce in ordinary light but an important exception is the green chlorophyll in plants, which does its work of photosynthesis using this property. https://en.wikipedia.org/wiki/Chlorophyll_fluorescence
 
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  • #5
Andy Resnick
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Specifically, do all color visible objects fluoresce? Whenever I aimed the 532nm Raman on color objects (such as red paint on a tin can), all I got are fluorescence which overlaps the small Raman signals.

Is this related to the fact that all colorful objects use paint in form of dyes and dyes can fluoresce? Can you give some list of colorful objects that won't fluoresce in visible light (using 532nm laser) so I can test this using Raman?

Also does this mean in everyday objects, there is continuous fluorescence from the visible light absorption and emission that we just don't see or distinguish with our naked eyes?
Everything fluoresces, but there are molecules that fluoresce more efficiently than others. Fluorescence and phosphorescence are two categories of luminescence; the difference between the two depends on the nature of the excited state.

If the excited state is a singlet state, the return to ground state is 'allowed' (selection rules) and the fluorescence lifetime is very short- 10 ns. If the excited state is a triplet, the relaxation back to ground is 'forbidden', and so phosphorescent emission rates are much slower- milliseconds to seconds.

As I said, all molecules fluoresce- I don't think atoms fluoresce because there are no vibrational/rotational states involved. The particulars of emission and absorption bands depend entirely on the molecule, which is one reason spectrophotometry is so useful.

Raman, Brillouin,, Rayleigh, and Stokes scattering processes are somewhat different from luminescence; Raman scattering is equivalent to the scattering of photons by (optical) phonons- Brillouin scattering is the scattering of photons from acoustic phonons.

Does that help?
 
  • #6
Awwtumn
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Everything fluoresces, but there are molecules that fluoresce more efficiently than others. Fluorescence and phosphorescence are two categories of luminescence; the difference between the two depends on the nature of the excited state.

If the excited state is a singlet state, the return to ground state is 'allowed' (selection rules) and the fluorescence lifetime is very short- 10 ns. If the excited state is a triplet, the relaxation back to ground is 'forbidden', and so phosphorescent emission rates are much slower- milliseconds to seconds.

As I said, all molecules fluoresce- I don't think atoms fluoresce because there are no vibrational/rotational states involved. The particulars of emission and absorption bands depend entirely on the molecule, which is one reason spectrophotometry is so useful.

Raman, Brillouin,, Rayleigh, and Stokes scattering processes are somewhat different from luminescence; Raman scattering is equivalent to the scattering of photons by (optical) phonons- Brillouin scattering is the scattering of photons from acoustic phonons.

Does that help?

Yesterday I spent 6 hours reading several dozen articles about fluorescence in Raman and hoped to find one where they explained how it differed to UV fluorescence of objects that you normally see, and how it is related to the absorption of objects (and reflection) in colors but I couldn't find anything that related them. So your message is very helpful.

fluorescence emission_.JPG


This is the diagram that almost all articles illustrated. The following is wikipedia's https://en.wikipedia.org/wiki/Fluorescence

Jablonski diagram.png


Text: "Jablonski diagram. After an electron absorbs a high-energy photon the system is excited electronically and vibrationally. The system relaxes vibrationally, and eventually fluoresces at a longer wavelength."

What I'd like to know is the following. In absorption of objects by visible light where for example the color red is reflected while all colors are absorbed (I know the basic concept of origin of colors). Does it mean that in common reflection of colors, there is also absorption from S0 to S1 and slight non-radiative transition (or relaxing vibrationally in S1) before it eventually fluoresces at long wavelength as it goes back to S0 (see above)? And we can't perceive this because it is not as distinct as when the source is UV light fluorescing to visible light in the typical fluorescence example that you commonly read?

About Raman. I'm familiar with Raman virtual state which is like virtual particles in that it doesn't really exist. But that should be another thread about Raman virtual state because I ponder if it doesn't exist and it is just perturbation series or math, why do we see the Stokes shift (or lower in frequency) with the other energy going to the realm of pure math (like Matrix).
 
  • #7
hutchphd
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There are many processes in condensed matter initiated by light quanta. A nontrivial subset of these involve fluorescence. A small subset of those involve Raman processes (although sometimes not called fluorescence) So the answer to your question is that much of what we see does not involve fluorescence and a much smaller fraction yet has anything to do with Raman scattering. Raman is a useful Laboratory tool.
 
  • #8
Awwtumn
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slider toys blue and red.jpg


I hit the above sliding toys with 532nm Laser in a Raman and the following are the spectra of each. This is the blue sliding toy showing the right Raman for the plastic.


spectrum blue slide.jpg



But when I hit the red sliding toy, there is no Raman signature detected, instead there is a broad Fluorescence.

spectrum red slide.jpg



I'd like to know the following. Please refer again to this illustration.

fluorescence.png


1. I know that colors work in the bulk in molecules. For single atoms, there is no color and instead the fine "color" is the spectrum of the atoms. And everyday colors only exist when they are in bulk molecules. When white light hit say blue object, I know all other colors are absorbed while the blue is reflected. But I want to know whether the blue that is reflected in the blue object first need to be excited to reach the S1 level above, then emitting the same blue wavelength (without any non-radiative transition?)

2. If it's yes above. Then both normal visible light reflection and fluorescence both reach the S1? The difference only the photons for the fluorescence have more energy?

3. Now when I hit the red slider toy with 532nm green laser, did the green wavelength photons reach S1 level, and upon non-radiative transition at S1 produce lower energy yellowish-orange photons as it goes down to ground state??

4. If yes to the the 3 above. What happens when I hit the blue slider toy with 532nm Green laser. There is much less Fluorescence that is why the Raman signal got through loud and clear. Does it mean the green laser can't reach the S1 level of the molecules of the blue slider toy? If it doesn't, it means no matter how strong the 532nm green laser you used, it just won't reach the blue S1 level (noting that blue has more energy than green).

Thank you!
 
  • #9
hutchphd
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The two toys are each made of the same plastic ( polyethylene? ) but each has a different colorant. The 532 nm laser does not interact strongly with the blue colorant (the blue toy would appear ~black or clear when in green light) whereas the red colorant will inelastically scatter the light.
I think your analysis is good in that the (Raman?) peaks seen from the blue toy are either overwhelmed by or outcompeted by the colorant in red toy. The process in the red toy is likely a mixture of fluorescence and other processes (but this is largely a semantic argument in which I will not participate)
.
 
  • #10
Awwtumn
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NORMAL COLOR TRANSITIONS.jpg


Back to my initial thread question. If ordinary color photons also get excited from s0 to s1 (is this correct? I added the ordinary color transition arrows in the above graphics. Can someone answer yes or no so I'm sure I understood it. Don't assume I know). Then for green wavelength photons from say white light, then it can also get excited from s0 to s1, and just like the laser, it can cause slight fluorescence in red objects, is this right?

Hope someone can answer this in the definite so I can like say in front to the class that fluorescence does not only occur for UV source but also for visible light for ordinary object like a red sliding toy but only imperceptible.

Or is this wrong because somehow the normal light green wavelength doesn't have enough energy to get excited from s0 to s1? But then, isn't it colors generally occur due to transition from s0 to s1?

Hope others can answer too because the incomplete answers of Hutchpdh is driving me nuts. I googled this all day but can't find this specific answer to the scenario above. Thank you.
 
  • #11
hutchphd
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Hope others can answer too because the incomplete answers of Hutchpdh is driving me nuts. I googled this all day but can't find this specific answer to the scenario above. Thank you.
I do not mean to cause angst but was quite careful to confirm that which was true. The rest will become mired in a sea of "is that really fluorescence" and life is short. I think you understand the Physics. To be sure then we would need to write some math. The rest is up to you.
 
  • #12
Awwtumn
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The reason I was asking for more details is because I couldn't find the answer of some questions after googling for days. For example. In the sliding toys of different colors:

slider toys.jpg


fluorescence compare.jpg


Why is there more fluorescence in violet versus that of blue or green in the wavelength fluorescence comparison above (exposure are all 600 milliseconds with 83 frames. The color of each spectrum (violet, blue, green) is the color of the toys themselves)? The violet energy levels between s0 and s1 are farther apart than blue or green. So how can the green laser 532nm even reach the transition levels of violet when it does poorly with blue? What is special about violet? It is a spectral wavelength, and not really close to red at all. Btw.. Red fluorescence is off the scale in the above so it couldn't fit.
 
  • #13
hutchphd
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Each colored plastic contains a different mixture of dye molecules. Why would you expect them to be the same?? They are not simple molecules nor are they necessarilly similar
 
  • #14
Awwtumn
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I guess the violet dye are made up of blue and red dye. If you know a dye that is truly violet without using mixes of blue and red dye, let me know.

Also today I learned that in ordinary color, all the rest are absorb and never emitted (except the color we see which got reflected without being absorbed). I thought before that the color we see everyday also got excited from S0 to S1 level. This is the reason I kept asking from beginning if the ordinary color we see also fluoresce since it goes from S0 to S1 too. So it does not because it never got excited from S0 to S1 at all. If someone only told me earlier.

Also it seems the photoelectric effect where frequency is involved is not related to the electronic transition from S0 to S1? Meaning even a long wavelength red photon can be excited from S0 to S1 of blue object if the energy is amplified like in red laser, right? Before I thought it was the frequency like in photoelectric effect that make electron get excited from S0 to S1 that is why I was thinking the green laser photons can't reach the blue electronic transition because the wavelength is not short enough. So this is wrong. Right?

I got interested in Raman now and borrow one to detect the thermochromic molecular makeup of the red burning bucket. But it seems there is no way to detect it now because the red just produces so much fluorescence. I don't want to use 785nm laser Raman because only 15% of the laser is visible and don't want accident exposure.
 

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