Spectralon fluorescence?

[Cadmium]

Spectralon fluorescence?

Well, You be the judge.

The one thing I might add is that after I shot these shots, I re-sanded the Spectralon (according to their directions) to make sure I had a clean pristine surface.

The sanding cleaned it up, yes, but the surface still fluoresced the same 'gray?' surface, same intensity, no difference other than the dust and smudges were gone.

 

Three shots of the Spectralon,

(left) Visual, camera has Zeiss T* + S8612 1.75mm on the lens.

 

(center/left) UVIVF #1, Spectralon and Straight-on torch shot, using Convoy S2+ 365nm Nichia with U-340 2mm filter on it, and the camera only has Zeiss T* on it.

Both Spectralon and Torch shots have the same settings.

 

(right)UVIFF #2, Spectralon and Straight-on torch shot, using Convoy S2+ 365nm Nichia with U-340 2mm filter on it, and the camera only has Zeiss T* + S8612 1.75mm (3.5mm) on it.

Both Spectralon and Torch shots have the same settings.

 

Settings are noted on test photos.

 

Direct head-on shot of U-340 2mm filtered Convoy/Nichia 365nm UV torch

These correspond directly to the photos below each torch shot.

Dark room. Some background fluorescence reflected off the left hand black torch glass filter front.

 

The first two shot/setting to the left correspond to the two left hand torch shots and setting above.

 

You decide. I don't want to think Spectralon fluoresces, so show me I am wrong.

[Andrea B.]

Spectralon is not supposed to fluoresce under UV light. But there are nuances to consider.

 

Spectralon reflectivity targets (as sold by either LabSphere or Ocean Optics) would be useless as reflectivity standards if they fluoresced.

 

Spectralon coatings would not be used in integrating spheres if the coating fluoresced. This would contaminate the signal being captured for any measurements involving UV light.

 

Here is a paper in which several Lambertian and specular reflective materials were analyzed for various properties. In particular, fluorescence under UV was examined for wavelengths between 220-600 nm in 5 nm steps. Spectralon did not fluoresce.

 

Clicking this link will load or download a PDF.

Reflectivity Spectra for Commonly Used Reflectors

by M Janacek, 2012

for OSTI.gov, the Department of Energy Office of Scientific and Technical Information

 

Here is a paper which looked at UVC fluorescence under assumptions somewhat more restricted than in the preceding reference. UV between 130-250 nm was used. Spectralon did not fluoresce in this analysis.

 

Clicking this link takes you to a Cornell U. website where you can download a PDF.

Photoluminescence Response of Acrylic (PMMA) and Polytetrafluroethylene (PTFE) to Ultraviolet Light

by Araujo, Pollmann & Ulrich

This seems to be a 2019 preprint from the Physics(?) Dept at Cornell University.

 

An interesting excerpt from the paper concerning contamination which can cause fluorescence in plastic materials.

 

Photoluminescence observed from a plastic is not necessarily due to the bulk material itself, but can be caused by impurities, defects or additives in the bulk material, or surface contamination.

Many common contaminants, such as oil from fingerprints, can fluoresce.

Residue from the sandpaper used to clean Spectralon could fluoresce.

 

---

 

So what has Cadmium photographed? I don't know. Perhaps the Spectralon is contaminated? Maybe, maybe not.

 

Please do remember that any light at all from the UV-LED torch or reflected from parts of the torch or reflected off the camera will be 99% reflected back by the Spectralon into the lens. So such experiments must be carried out with great care so as not to have any nearby fluorescing or reflecting stuff. That was an error I made myself a few years back when I photographed my Spectralon against a background of fireplace bricks which had some fluorescent patches.

(Do any parts of the torches themselves fluoresce? Or any labeling?)

[Cadmium]

So, I got thinking.

What if the light from the spectralon is maybe coming from low ambient florescence from around the rest of the rood? Right?

So one way to test that is to shoot some photos of the torch right up close by the spectralon, where non of the beam was overlapping the target,

the convoy hot spot is well within the spectralon target, no other fluorescence around the room.

Results? Same thing.

Lets go over this again.

Specralon illuminated by U-340 2mm filtered 365nm UV, no lights, no other fluorescence in the room. Zeiss T* + S8612 1.75mm on the camera.

Then I added to that, the bottom two photos on the bottom row, these have the torch with the U-340 2mm and ALSO filtered with S8612 2mm and S8612 3.5mm,

so those two should be illuminated by nothing other than UV (S8612 on the camera and on the torch), double safe.

 

 

You figure it out. I can't.

[Cadmium]

On 12/3/2020 at 1:31 AM, Andrea B. said:

Spectralon is not supposed to fluoresce under UV light. But there are nuances to consider.

 

Spectralon reflectivity targets (as sold by either LabSphere or Ocean Optics) would be useless as reflectivity standards if they fluoresced.

 

Spectralon coatings would not be used in integrating spheres if the coating fluoresced. This would contaminate the signal being captured for any measurements involving UV light.

 

Here is a paper in which several Lambertian and specular reflective materials were analyzed for various properties. In particular, fluorescence under UV was examined for wavelengths between 220-600 nm in 5 nm steps. Spectralon did not fluoresce.

 

Clicking this link will load or download a PDF.

Reflectivity Spectra for Commonly Used Reflectors

by M Janacek, 2012

for OSTI.gov, the Department of Energy Office of Scientific and Technical Information

 

Here is a paper which looked at UVC fluorescence under assumptions somewhat more restricted than in the preceding reference. UV between 130-250 nm was used. Spectralon did not fluoresce in this analysis.

 

Clicking this link takes you to a Cornell U. website where you can download a PDF.

Photoluminescence Response of Acrylic (PMMA) and Polytetrafluroethylene (PTFE) to Ultraviolet Light

by Araujo, Pollmann & Ulrich

This seems to be a 2019 preprint from the Physics(?) Dept at Cornell University.

 

An interesting excerpt from the paper concerning contamination which can cause fluorescence in plastic materials.

• Photoluminescence observed from a plastic is not necessarily due to the bulk material itself,
  but can be caused by impurities, defects or additives in the bulk material, or surface contamination.
• Many common contaminants, such as oil from fingerprints, can fluoresce.
• Residue from the sandpaper used to clean Spectralon could fluoresce.

---

 

So what has Cadmium photographed? I don't know. Perhaps the Spectralon is contaminated? Maybe, maybe not.

Please do remember that any light at all from the UV-LED torch or reflected from parts of the torch or reflected off the camera will be 99% reflected back by the Spectralon into the lens. So such experiments must be carried out with great care so as not to have any nearby fluorescing or reflecting stuff. That was an error I made myself a few years back when I photographed my Spectralon against a background of fireplace bricks which had some fluorescent patches.

(Do any parts of the torches themselves fluoresce? Or any labeling?)

 

You keep saying that, but my Spectralon is not being illuminated by anything other than UV.

Show me how your spectralon doesn't fluoresce, doesn't have some illumination from UV only.

Perhaps I have some weird spectral that was soaked in some kind of fluorescent goop?!

This is fluorescence, just like the way Bob's oak table fluoresces, not something bright like a Grateful Dead poster, but something that you would never think of as fluorescent.

This is fluorescence.

Show me spectralon that doesn't fluoresce.

[Andrea B.]

As I said, I don't know what is happening in your photos. The above linked experiments and the company LabSphere itself say that Spectralon does not fluoresce. Mine doesn't fluoresce. It just looks kind of dull purple under my "nichia torch". I will put it on my Todo list to re-photograph the standards using U-340 filtration on the older (non-Convoy) torches.

 

My previous exposures (in the other thread) were f/8 for 1.6 sec @ ISO-400. Yours are f/6.3 for 8 sec @ ISO-200. How many stops difference?

 

It isn't *me* you are disagreeing with. I'm only stating facts from science papers and from LabSphere.

[colinbm]

As I said, I don't know what is happening in your photos. The above linked experiments and the company LabSphere itself say that Spectralon does not fluoresce. Mine doesn't fluoresce. It just looks kind of dull purple under my "nichia torch". I will put it on my Todo list to re-photograph the standards using U-340 filtration on the torches.

 

My previous exposures (in the other thread) were f/8 for 1.6 sec @ ISO-400. Yours are f/6.3 for 8 sec @ ISO-200. How many stops difference?

 

It isn't *me* you are disagreeing with. I'm only stating facts from science papers and from LabSphere.

 

All the surfaces in his UV lit photos are fluorescing from grubby surfaces.

[Andrea B.]

Forgot to mention.

I have some older lenses here on which the white lettering around the inside of the front rim shows some fluorescence. One of my Petri lenses, for example, has a very brightly fluorescent red-orange "K.C." !! But this is not a lens which I would typically use for UVIVF.

 

The red mark for IR adjustments on some of these lenses also fluoresces a bright orange-red. But that is on the side of the lens, so probably plays no role in contamination of UVIVF.

 

Point being that we have to look at all the gear in use to make sure there are no fluor parts.

[Andrea B.]

---

....grubby surfaces.

 

Mine look like that also. UV really brings out surface details.

---

 

Here is my doubly-filtered photo from the other thread.

 

Nikon D-600-conversion.

"Nichia torch" with BaaderU filtration.

Baader UV/IR-Cut on Zeiss UV-Planar 60/4.0 lens.

f/8 for 1.6" @ ISO-400

 

And, no, I should not have had the targets (at bottom) in this photo.

But my result is certainly not bright like Cadmium's.

 

As I said, I don't know what's going on.

 

Some reflected violet as seen with Daylight WB setting.

[Cadmium]

Andrea, I don't know what is going either, but your results above coincide with mine, seems to me. What you show there is exactly what I am talking about.

I have the 6 gradient set, 99 is the whitest, the black one hardly fluoresces at all, it is almost pure black, and likewise, each whiter one is a little more fluorescent.

If you know where they say these don't fluoresce, I would like to read that. I looked for something about that, and wasn't able to find anything about that.

 

Look at this test. I don't think anything gets through this monster stack, except of course UV.

This stack is a total of 18mm of U-340 + the Baader U + S8612 3.5mm. That blocks everything, except UV.

Then on the lens I have the UV blocking Zeiss T* + another S8612 2mm filter for visual only range.

And nothing else in the room is even barely illuminated or fluorescing.

That white area and the hot spot on the Spectralon is coming directly from the UV beam that is passing through that Time Tunnel (remember the Time Tunnel TV show?).

I call it fluorescence. But then I think almost everything I can find fluoresces some.

 

So here it is.

 

[JMC]

Makes me wonder if there is a small amount of something in the binder - if there is a binder - for the Spectralon which is causing the fluorescence. At the moment I've no real idea about what causes this.

 

And I see similar behaviour to you too Steve (and Andrea).

[Andrea B.]

I *love* our forum !!! We have such interesting discussions.

 

I think a call to Labsphere is in order. Today is a Domestic Duties and House Chore Day, but I'll add the call to my Todo list. Also I promised to review something today, so I have to do that first.

 

 

Cadmium, that is *terrific* with the 18mm of UV blockers. May I please have permission to use your photo when contacting Labsphere.

 

Jonathan, a good question to ask. But again, Spectralon would hardly stand as a UV/Vis/IR reflective target or an integrating sphere coating if the binding agent fluoresced.

[Stefano]

It may be a dumb idea, but if someone has snow, you can use it for comparison purposes as snow really does not fluoresce.

 

What is the difference between Spectralon and pure PTFE? Isn't it made of PTFE?

[Andrea B.]

Look up Spectralon in Wikipedia.

[Stefano]

Quote: "The material consists of PTFE powder that has been compressed into solid forms and sintered for stability, with approx. 40% void volume to enhance scattering of light."

 

There isn't any mention of binders or other substances.

 

Sintering

 

Quote: "Sintering or frittage is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction."

[Andy Perrin]

Could we be dealing with a case of thresholds here? Like, suppose the Spectralon people regard something that fluoresces below some particular value of luminance as "non-fluorescent" and their Spectralon is below that value.

[JMC]

So the PTFE is pressed together. How pure is it? 99%, 99.9%, 99.99%??? Even tiny amounts of anything that isn't pure PTFE could be leading to the observed fluorescence. The grey and black standards presumably have something which isn't PTFE in there as PTFE is white.

 

For instance, an older paper here - http://hep.ucsb.edu/people/hnn/n/uvcontampfte.pdf

 

In the paper above they talk about the presence of impurities in the Spectralon, and that these can be photodegraded by VUV. We don'y use VUV but the key thing is that even in something seemingly as pure as this there will be impurities, either from the raw materials being used, the manufacturing process, or storage afterwards. Any one of these could be responsible for the observed fluorescence, or it could be something else entirely.

 

As we get more and more powerful UV sources and better and better filtering of the UV itself to remove the visible, it's not surprising to start finding weaknesses in materials, especially as more and more people start playing with them.

[Andrea B.]

Cadmium, what is your Spectralon mounted in? Does it have a back?

[Cadmium]

This is getting interesting. Thanks to all of you for discussing this.

The idea I think, is that if something doesn't fluoresce, then it should appear black. Would you agree?

I wrote Labsphere and got a reply today. They said what I I had expected, 'Spectralon does not fluoresce'. It is PTFE and air, they said.

It can get contaminated, etc...

I remind you of my comparison between white virgin PTFE sheet and Spectralon (below), see how they both fluoresce, they are quite the same,

one of the big differences is sheet has a shiny surface. The sintered structure of Spectralon provides a much better uniformity in varied light sources and direction,

no surface reflection to deal with, for me that is the big plus when it comes to Spectralon. When I compare Spectralon and PTFE I get the same fluorescence.

 

However, I have seen somewhere other info showing more than just simply PTFE that goes into the Spectralon mix,

I think it is a bit more complicated, and the "PTFE and Air" is a simplified description.

I know they are mixing something in for the other darker versions, so I would probably guess they are mixing in something for the white also.

PTFE powder can be found on eBay, is used for lubricant, pianos... etc..

You can compress it under a regulated amount of consistent pressure for whatever amount of time while held at whatever controlled sintering temperature,

and it would render something similar to Spectralon, but with no other ingredients. The powder, looks the same as Spectralon also, same fluorescence.

I don't think you need a binder, sintering heats something up to just under the melting point, but hot enough to bind the particles together under pressure.

https://en.wikipedia.../wiki/Sintering

 

Another idea is that their mixture may have changed over the years, and mine may be older. But that is just a random side thought.

 

By the way, I replied back to Labsphere with some of these photos above, but received nothing back (so far) from them in reply to the photos.

Always, when I have photographed PTFE in UVIVF it has appeared the same gray/brown/whatever depending on white balance, but definitely not black,

and also not white when illuminated with pure UV light only. The same is true of Spectralon.

 

I think it would be good if we can come to some conclusion and not simply depend on Labsphere's stock answer. Either they are wrong when it comes to our use at least,

or we are wrong and doing something wrong, or missing something we should be thinking about. Because if something is fluorescing that should look black,

then perhaps we have missed something in our thinking?

 

Yes, Andrea, you can always use my photos.

 

Again, I would say that pretty much everything fluoresces some.

Stefano said it here, and I think Andy agreed?

https://www.ultravio...dpost__p__40166

 

The blackest thing I have found in UVIVF is the my Spectralon SRS-02-020, it will barely fluoresce at all, only when you get the torch close to it,

and would probably need a very long exposure time to show that, and it might not even do it at all if I isolated everything the way I have above.

 

See the fluorescence different between Spectralon and PTFE.

The black in the background is the Krylon 1602 ultra flat black spray paint on brown cardboard, the blueish it the top of my dryer (in my test lab).

(I tell ya, that Krylon 1602, great stuff, SO black in reflected UV or anything else)

[Cadmium]

Cadmium, what is your Spectralon mounted in? Does it have a back?

 

The usual round black metal container. There is a label on the back of each one. 2 inches diameter.

Mine look like the actual Spectralon is about 12mm thick (?) if I subtract what I think the thickness of the metal is on the back of the metal container.

Mine look like these, and are all listed on this list.

https://www.labspher...2_standards.pdf

 

 

[colinbm]

Spectralon has 40% void....a great place for contaminants to collect......

PTFE is also recommended to 'clean' & abrade on a flat surface, to bring up a 'fresh' surface to measure from.

[Cadmium]

Thank you Colin.

I don't think this is a situation of cleaning, everyone is getting the same results, and I think we have all cleaned out Spectralon at some point or other, and tested them after cleaning.

Besides, the fluorescence of clean or dirty Spectralon looks the same as PTFE sheet which is not porous.

If you don't treat your Spectralon with some respect, it will get dirty and require more sanding than not.

 

http://labsphere.com/site/assets/files/2569/an-13011-000rev00.pdf

[dabateman]

Jonathan

If you have a similar spectralon with similar UV fluorescence. See if you see anything under your reflection microscope at your highest magnification at the fluorescent spots. I wonder if something could be eating off it or if there is just some dust trapped inside with similar dust like contaminants we see when trying to set up a UV induced image.

Dust always seems to be everywhere. But could also be something growing on the surface. Microbes can grow anywhere.

[Stefano]

David, you made me think about something we usually take for granted: is the air clean? Do they sinter Spectralon in purified air? Because if they use normal air, I can think of dust being trapped inside.

[Cadmium]

If they 'say' it is made of PTFE and air, but don't tell us anything else is in it, then let me ask you why they would make it out of PTFE when PTFE fluoresce?

Would they put something in the mix to make the base material not fluoresce? I have a bit of a struggle with that idea.

If PTFE fluoresces, then Spectralon fluoresces by default, and if you have some magic powder to mix with something that fluoresces, to cancel out the fluorescence, then... ?

Best to get a new one, test it, better approach, don't waste time, test a new one see if there is a difference. You need a new one anyway, right? To test the old one, right?

 

It seems possible to me that what they call fluorescence is not exactly the same as what we call fluorescence.

[ulf]

My guess is that the Spectralon is made of super pure PTFE.

The purity of materials differ and super pure is for normal applications not needed.

 

Compare with different types of glass.

Normal glass used in windows can be rather green, when seen from the edge, while glass used in fiber optical cables must have much better transmission.