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Total Tek Nerd-Out - Spectroscopy files and images
https://gemologyonline.com/Forum/phpBB2/viewtopic.php?f=22&t=6337
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Author:  jleb [ Thu Jul 31, 2008 4:24 pm ]
Post subject:  Total Tek Nerd-Out - Spectroscopy files and images

I'm slavering over all this good stuff! Brian, transmission spectrums on everything, and you get to contribute. I've just opened the vug up, still digging through it all.. :lol:

http://minerals.gps.caltech.edu/FILES/index.html

Everything about tourmaline!

http://minerals.gps.caltech.edu/FILES/V ... /Index.htm

The home page:

http://minerals.gps.caltech.edu/index.html

enjoy!

Author:  Brian [ Fri Aug 01, 2008 2:02 am ]
Post subject: 

They are absorbance spectra, not transmission spectra. You can think of an absorbance spectrum as an upside-down transmission spectrum. For those geeky enough to want to convert the data into a transmission spectrum: load the two-column XY absorbance data in excel. At each wavelength X, there is an absorbance value Y (which is less than 10). Then the transmission value Z = 10 - Y. Plotting Z vs X gives the transmission spectrum.

Experimentally, they must scan the wavelength of the light source to produce these spectra. Looking at their ruby spectra, the 695 nm Cr ion feature appears as an absorption rather than a fluorescence. As I mentioned in a recent physics talk, if only red light is available then the Cr ion feature will appear as an absorption, whereas when all wavelengths of visible light are available then the Cr ion feature will appear as a fluorescence.

Also looking through the beryl spectra, it is interesting to see they all show a narrow absorption feature at 950 nm (in the IR). As the website says "In the spectra of all these minerals, sharp features in the near-infrared region arise from water molecules in the c-axis channels of the beryl structure." I think Gem├ža also made this point either in the Beryl or Emerald thread in this research section.

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