254nm-Induced Fluorescence Trial – You Win Some, You Lose Some

[bvf]

In the post at https://www.ultravio...-your-rocks-of/ I showed results of fluorescence exhibited by some rock samples using both UV (Nemo torch) and visible excitation. The subsequent comments raised the idea of using a low-cost 254nm UVC lamp to see if that gave different output.

 

So I got myself one of these rom China: https://www.ebay.co....872.m2749.l2649 . A few weeks later it arrived – but the filter was chipped along the edge and leaking light, and the filter housing wouldn’t close properly. The supplier said something like “Yes, happens all the time. But it will be OK.” Anyway, they sent me a new filter, which I cemented to the outside of the housing, and off we go.

 

Health warning:

UVC is dangerous. There’s plenty of advice on the forum about protecting yourself using glasses, cotton clothing, etc. In addition I took two precautions:

1. Adapted the lamp to run off external power and used the cameras on WiFi remote control, to let me operate from a different room.
   
2. As the lamp needed several minutes to fully “warm up” it was impracticable to turn the lamp off between each shot. So I made a simple cardboard sleeve to slide over the lamp so I could work nearby to set up the camera and target.
   

 

UV and IR Colour Images:

In UV and IR false-colour images below, the following colour assignments have been used:

• Red Channel UV: 380nm
  
• Green Channel UV: 345nm
  
• Blue Channel UV: 315nm
  

• Red Channel IR: 1000nm
  
• Green Channel IR: 850nm
  
• Blue Channel IR: 750nm
  

The lamp:

It became clear that the lamp and its filter leak a lot of non-254nm wavelengths. I tried to get fluorescence output at UVA wavelengths, but the images were almost entirely like reflected light images, although there was a hint of fluorescence output – results later.

 

More surprisingly, there was a lot of IR leakage too. The IR output results looked totally like reflected light images with no hint of fluorescence. I have not bothered to post any results here.

 

Fortunately the visible output was reasonably good – but the fluorescence is being excited by multiple wavelengths, not pure 254nm.

 

The following images give an idea of the leakage. In each case, the upper image used exposure similar to that used to make the fluorescence images, and the lower image is at a lower exposure to show the colour of the leakage. The colour images were WB-ed for sunlight.

 

Visible Output:

 

 

UV Output:

 

 

IR Output:

 

 

I also used one of Stefano’s tests (see https://www.ultravio...-265-nm-uvc-led ) to judge how strong the 254nm lamp output was. Pure 254nm (or at least below about 320nm) would render the magnifying glass as pure black. My conclusion is that there is a lot of 254nm, but there are longer wavelengths as well. In each case, the upper image is against paper (fluorescing) and the lower image against PTFE (probably non-fluorescing).

 

Visible:

 

 

 

UV (lower image's exposure was 7.5x upper image's exposure):

 

 

 

IR:

 

 

 

Results

 

254nm-Induced Visible Fluorescence

 

When looking at output in the visible range, some targets look the same whether excited using the Nemo torch or the 254nm lamp. But in some cases there was some additional green fluorescence.

 

The top images are normal visible images, the middle images are UVIVF made using the Nemo torch, and the lower images are UVIVF made using the 254nm lamp.

 

Rainbow Flourite

I assume the fluorite is the main bulk of the sample, and the white/green areas are something else adhering to the fluorite. So the fluorite fluoresces consistently blue, but the “something else” shows green under 254nm.

 

 

 

 

Group 3

What’s really noticeable here is the appearance of green in the Aragonite and yellow calcite, and the whitish fluorescence in the blue calcite (bottom left).

 

 

 

 

254nm-Induced UVA Fluorescence:

 

As mentioned above, these images are largely reflected-UV images, but we can see some fluorescence. The predominance of green indicates fluorescence output around 345nm.

 

The top image is a normal visible image, the middle image is a “normal” tri-colour reflected UV image, and the lower image is UV-Induced UVA Fluorscence made using the 254nm lamp. In all cases, WB was against the PTFE background.

 

Rainbow Flourite

 

 

 

 

Pink Aragonite

 

 

 

 

Group 1

 

 

 

[Stefano]

Interesting. It isn't easy to get pure 254 nm UVC from a mercury-vapor lamp. Ionic glass filters won't help. You would need to put a dichroic/interference filter (similar to a Baader U) on your lamp, that passes only UVC while blocking at least the other UV wavelengths. UVC LEDs aren't pure either, but maybe there is less contamination (my glass tests were probably darker than yours, even if my phone camera could have made the blacks blacker than they really were, I still saw a bit of light coming through with my naked (protected) eyes) and they are easier to filter (but are much weaker and harder to work with unless you have a pre-made all-in-one lamp).

 

MaxMax sells filtered 254 nm lamps, but I don't know if they are pure enough for your project.

[dabateman]

Well definitely some differences with the 254nm light. Thus why most rock hunters have a 254nm and 365nm light source on hand.

I think they use a 1mm Zwb3 filter from my tests of mine. That doesn't cut much. If you have 6mm of ZWB3, that should cut out all the visible, but not UV or IR. The problem is there isn't a cheap 254nm centric option. Also anything that seems to cut IR will also cut out the 254nm peak. So unless you're willing to spend thousands of dollars on a tight dichoic filter, zwb3 is the cheapest alternative.

 

I do like the images and now you have something to play with.

[colinbm]

Great to see the differenced Bernard

[microbat52]

That fluorite is so cool. And the different aragonite fluorescence!

 

Interesting info here:

 

https://www.fluomin.org/uk/fiche.php?id=87