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Getting Your Rocks Of ...: Fluorescence Rocks


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I’ve completed my first fluorescence project. The idea was to look at fluorescence patterns of various rock samples under different excitation and output bands. This images are not very exciting from the artistic point of view (esp. when compared with the other excellent fluorescence images posted on UVP), but the objective was to extract information rather than create aesthetic images.

 

Here are the results (based on a Powerpoint I put together for a geoscientist friend who’d given me some guidance and wanted to see how I got on).

 

Filters and lighting had been discussed in another post on UVP – the actual lighting, filters, and camera used are listed after the images.

 

I was a bit disappointed that the spectrum of the output does not generally vary with the colour of the excitation, so you don’t seeing much difference whether the excitation is UV or visible, or whether the generated fluorescence is in the visible or IR bands. Typically I started doing desk research after I’d spent time on the experimental work, and found the following on Wikipedia:

 

Kasha's rule ... The Kasha–Vavilov rule does not always apply and is violated severely in many simple molecules. A somewhat more reliable statement, although still with exceptions, would be that
the fluorescence spectrum shows very little dependence on the wavelength of exciting radiation
.

 

So it looks like the results are in line with expectations.

 

In some scenarios there is some filter leakage (even where the graphs indicated it wouldn’t be a problem) and background light pollution (as I didn’t have anything like a cellar to work in). So some scenarios could not be achieved where the level of fluorescence was too low: e.g. when creating the tri-colour IR images the exposure through the 1000 nm filter (red channel) was 400 x the exposure through the 750 nm filter (blue channel), which became an impossible task when combined with putting bandpass filters over the light source.

 

For Visible induced Visible Fluorescence, I mitigated the effect of filter leakage by making two exposures: (1) the fluorescence exposure using the filters described below, and (2) a second exposure with the camera and illumination filters swapped over. The second exposure should record approximately the same leakage, but would not record any fluorescence. Then I took the difference between the two images in post-processing.

 

Anyway, here are the results.

 

post-245-0-70104100-1609250214.jpg

 

post-245-0-51255100-1609250220.jpg

 

post-245-0-35184000-1609250227.jpg

 

post-245-0-58696800-1609250238.jpg

 

post-245-0-28642100-1609250247.jpg

 

post-245-0-16476600-1609250255.jpg

 

post-245-0-03753900-1609250266.jpg

 

post-245-0-29413400-1609250272.jpg

 

post-245-0-64670300-1609250284.jpg

 

post-245-0-08483600-1609250296.jpg

 

post-245-0-47408500-1609250303.jpg

 

post-245-0-84570800-1609250313.jpg

 

post-245-0-68172400-1609250321.jpg

 

post-245-0-48549100-1609250329.jpg

 

post-245-0-75339400-1609250339.jpg

 

post-245-0-53377400-1609250349.jpg

 

post-245-0-62398400-1609250356.jpg

 

………………………….

 

Lighting and Filters

 

For UV excitation:

 

Lightsource: Nemo UV torch, with in-built filter

 

Filter: Baader U supplementary filter

 

For Visible excitation:

 

Lightsource: Lumitact G700 torch

 

Filters for White excitation for IR fluorescence: Baader UV/IR Cut + Unbranded UV/IR Cut + Tiffen 2A

Filters for Blue Excitation for IR fluorescence: Baader UV/IR Cut + Midwest Optical BP470

Filters for Green Excitation for IR fluorescence: Baader UV/IR Cut + Midwest Optical BN520

Filters for Red Excitation for IR fluorescence: Baader UV/IR Cut + Midwest Optical BP635

Filters for Blue Excitation for Visible (Red) fluorescence: Midwest Optical BP470 + S8612 + Kodak 80A

Filters for Green Excitation for Visible (Red) fluorescence: Midwest Optical BN520 + S8612 + Kodak 80A

 

 

Cameras and Filters:

 

For Visible Fluorescence:

 

Camera: Non-modified Canon EOS 6D II, Canon EF 50mm f/1.8 lens

 

Filters when capturing all visible fluorescence (UVIVF): Baader UV/IR Cut + Tiffen 2A

Filter when capturing red fluorescence from Blue or Green excitation: Baader UV/IR Cut + R25 + Midwest Optical BP635

 

For IR Fluorescence:

 

Camera: Sony A6000 modified for full spectrum, Canon EF 50mm f/1.8 lens

 

Filters for Blue channel image: R72 + Midwest Optical BP735

Filter for Green channel image: Midwest Optical BN850

Filter for Red channel image: Midwest Optical LP1000

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Yes, the work was spread over a couple of weeks, bearing in mind I had to wait until it was dark outside and had to repeat quite a few of the exposures (up to 12.5 minutes each) when things went wrong - such as my wife switching on the light outside the bathroom. But then, what else is there to do in winter?

 

Now I need to find some more interesting subjects ...

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You might want to try the other way around, try find molecular energy charts where the excitation levels are separate enough to require a photonic relaxation and that are within IR and UVC. Then you might be able to find specimens that fluoresce in different wavelenghts for different excitation.

 

Unfortunately I got rid of my molecular chemistry books a decade ago and my brain deleted 90% of what I learned.

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Bernard you do have some intensity differences.

I am not sure about 365nm vs visible, but 254nm will have differences.

You can get a cheap 254nm short wave rock light fairly cheap, most have a filter over the 4W bulb. Might be fun to add.

 

Andrea had some interesting rock group links I remember.

 

 

https://www.ebay.com/itm/254nm-Shortwave-UV-Light-Mining-Glow-Rock-Stamps-Detection-Ultraviolet-Lamps-/254721135365?_trksid=p2349624.m46890.l49292

 

 

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Thanks, David. I wasn't aware of those shortwave UV lights.

 

Anyway, I've ordered one. I suspect it'll be too weak for tri-colour IR fluorescence, but we'll see. Perhaps it'll also work as a Covid-zapper!

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BTW - what filter do you think they fit to the lamp? The ZWBx family do not perform well at 245nm (about 10% transmission for ZWB1, 1.1% for ZWB2, 30% for ZWB3) ?
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In my 265 nm LED topic I advised UG5/U-330/ZWB3 for 265 nm. A mercury lamp emits a bit lower at 253.7 nm, but that's the best (ionic) filter you can have. You have to remove the 365.4 nm I-line, the 404.7 nm H-line, the 435.8 nm G-line and the green 546.1 nm line. They are quite weak in a low-pressure lamp, and the last two lines (G and green) are responsible for the bluish-cyan glow these lamps have.

 

You can not have a perfectly clean spectrum without sacrificing a good amount of output, but you can at least remove some of those lines.

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Depends on the thickness. 1.5 mm thick U-330/UG5 still transmits more than 70% at 254 nm. I don't know why you are saying 245 nm. Mercury emits at 254 (253.7).
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It depend on how much you want to suppress the visual lines from the tube. Sometimes I think 2 or even 3mm ZWB3 is used, even if that attenuates the UV-C more.

If a low pressure tube is used the ratio between 254nm and 365nm peaks are quite good.

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