The Naked Scientists

The Naked Scientists Forum

Author Topic: Determining UV wavelength by fluorescence  (Read 4541 times)

Offline yardleydobon

  • First timers
  • *
  • Posts: 2
    • View Profile
Determining UV wavelength by fluorescence
« on: 10/07/2009 02:27:18 »
I would like to determine the spectrum of a UV LED. I've made a CD spectrometer
calibrated with a CFL and used ImageJ to get a rough spectrum. The tails of the
spectrum fizzle out at around 380 and 440 nm. I'm not certain I trust the shorter
wavelength tail because of the filtering effect of the polycarbonate, the lens,
and the UV filter over the CCD.

If I had a list of maximum wavelengths at which fluorescent materials fluoresce
I could get an idea of where the shorter wavelength tail is. For example, if
vitamin B12 will fluoresce up to 370 nm and vaseline up to 375 nm, and the LED
causes the vaseline to fluoresce but not the vitamin B12 then I know the tail is
in that region.

Is this doable? Is there a list somewhere that lists the wavelengths at which a
fluorophore will stop fluorescing? I would like to use household products like in
the following list if possible: newbielink:http://chemistry.about.com/cs/howthingswork/f/blblacklight.htm [nonactive]
Using some like Alexa fluors could work for me if they are inexpensive and can be purchased
over the internet.

What about UV photochromic beads? I've read these change in the interval 360-300 nm.
I have a few of these.  I shined the light on them and only the purple changed color.
The light blue and peach stayed white. So it appears that the colors activate at different
wavelengths. Can someone tell me at what wavelength each color changes?

Please help! I've googled this problem to death. ???



 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8655
  • Thanked: 42 times
    • View Profile
Determining UV wavelength by fluorescence
« Reply #1 on: 10/07/2009 16:59:22 »
If you are looking for things that glow when hit with near UV light there are plenty. They get used for detection of short wave UV and are called wavelength shifters. Some odd chemicals are used for this but I think that the fluorescent dyes in most soap powders and white paper would probably do the job. You could also use sodium salicylate (obtained by the hydrolysis of aspirin) or extract of horse chesnuts
http://en.wikipedia.org/wiki/Esculin
which was the first UV brigtener.

If you want a compound that absorbs or emits at a particular UV wavelength then it's more difficult as the basorbtion bands are not generally very sharp.
 

Offline yardleydobon

  • First timers
  • *
  • Posts: 2
    • View Profile
Determining UV wavelength by fluorescence
« Reply #2 on: 10/07/2009 22:29:12 »
I want to determine the shortest wavelength of an LED.

Quinine will fluoresce at 350 nm. If I shine the LED on quinine
and it fluoresces I know the the LED puts out 350 nm. If I then
shine the LED on another material that fluoresces at 340 nm and
nothing happens then I know the LED does not put out 340 nm.

I believe this oversimplifies things in two ways:
1) the excitation spectra of fluorophores do not drop off like
   a brick wall.
2) the LED may put out the correct wavelength to cause fluorescence
   to occur but the intensity at the wavelength is not enough to
   make the fluorescence noticeable.

I suppose what I need is the excitation spectra of common household
items that fluoresce when excited by UVA. However it would be enough
if someone could give me a list of common things that looks like this:

Fluorophore    Fluoresces   No Fluorescence
AAA            340 nm       350 nm
BBB            345 nm       365 nm
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8128
  • Thanked: 53 times
    • View Profile
Determining UV wavelength by fluorescence
« Reply #3 on: 10/07/2009 23:22:56 »
Cameras can see UV, but special lenses are required (ordinary glass blocks UV)...

Quote
Most types of glass will allow long wave UV to pass, but absorb all the other UV wavelengths, usually from about 350 nm and below. Only special developed lenses made of quartz (fused silica) or quartz and fluoride can be used. Using these lenses allow the camera to reach the range 180..200 nm. Lenses based purely on quartz show a distinct focus shift between visible and UV light, whereas the later developed fluoride/quartz lenses are fully color corrected without focus shift. Examples of the latter type are the Nikon UV Nikkor 105 mm, the Hasselblad (Zeiss) UV Sonnar 105 mm and the Asahi Pentax Ultra Achromatic Takumar 85 mm.
http://en.wikipedia.org/wiki/Ultraviolet_photography#Reflected_UV_photography
 

The Naked Scientists Forum

Determining UV wavelength by fluorescence
« Reply #3 on: 10/07/2009 23:22:56 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums