SPOTLIGHT: ALBERTO SCARANI, GG, FEATURED PRESENTATION: SYNTHETIC DIAMONDS DEMYSTIFIED: AGA LAS VEGAS, JUNE 1
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Sun May 20, 2018 3:34 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 34 posts ]  Go to page Previous  1, 2, 3
Author Message
 Post subject: Re: NIR absorbance spectra of tourmaline
PostPosted: Fri Oct 28, 2011 12:21 pm 
Offline
Valued Contributor

Joined: Wed Oct 22, 2008 5:00 am
Posts: 344
Location: Finland
Congrats for beating the nasty IR stray Albe =D>

Yes, Cu2+@ 900nm is obvious and if one looks careful enough the ~700nm Fe2+ / Cu2+ is also detectable as a shoulder. Small peak at ~410nm is possible sign of Mn2+

_________________
GemmoRaman GemmoFtir GemmoSphere


Top
 Profile  
Reply with quote  
 Post subject: Re: NIR absorbance spectra of tourmaline
PostPosted: Fri Oct 28, 2011 12:29 pm 
Offline
Site Admin
User avatar

Joined: Fri May 12, 2006 11:24 am
Posts: 7487
Location: Rome, Italy
mikko wrote:
Congrats for beating the nasty IR stray Albe =D>


thx mate.

Quote:
Yes, Cu2+@ 900nm is obvious and if one looks careful enough the ~700nm Fe2+ / Cu2+ is also detectable as a shoulder. Small peak at ~410nm is possible sign of Mn2+


yup, checked the stone in different positions, this one shows more distinctively the 900 feature, others displayed a little better the 700 shoulder....

ciao
albé

_________________
GemmoRaman-532 - GemmoFTIR - GemmoSphere - EXA


Top
 Profile  
Reply with quote  
 Post subject: Re: NIR absorbance spectra of tourmaline
PostPosted: Fri Oct 28, 2011 2:03 pm 
Offline
Gemology Online Veteran

Joined: Thu Sep 25, 2008 10:33 am
Posts: 750
Location: Mars PA
I believe that the curve indicates copper in a blue/green tourmaline. I just looked at an absorption graph done by a Swiss Laboratory on my best blue/green cuprian tourmaline (the gemstone has been tested by LA-ICP-MS and shown to be copper bearing) and one of the axis (a/b)shows a similar curve) while the c axis has a higher peak at 700 nm and the 900 nm peak is increased some, but not as much as the 700 nm peak (ratios would be different between the 700nm and 900 nm depending on axis). If the gemstone was purple or red/pink I would have some reservations about the gemstone definitely being cuprian because of the Mn+3 absorption around 900nm. It would be interesting if you could get absorption curves for the c axis and a/b axis to see the differences in them. All my cuprians that have been tested by outside laboratories have shown different curves even when I can not see any difference by eye. I have not made any effort to change axis with my set up. My best blue/green cuprian is not dichroic by eye.

Keep up the good work and good luck with tourmaline.

Bruce


Top
 Profile  
Reply with quote  
 Post subject: Re: NIR absorbance spectra of tourmaline
PostPosted: Mon Oct 31, 2011 3:02 pm 
Offline
Gold Member
User avatar

Joined: Mon Apr 16, 2007 12:05 am
Posts: 1439
mikko wrote:
Congrats for beating the nasty IR stray Albe =D>

I too think it must be a bit of stray light getting into the spectrometer that had not first passed through the stone. Such stray light definitely causes anomalous structure to appear in a spectrum.

Another indication that stray light not passing through the gem is the cause of the problem can be seen in the 900-1000 nm region of the two spectra. From my recent experience, incandescent and halogen lamps produce very low intensity beyond 900 nm, so that the spectral data should jump around quite a bit in this region. We can see this is exactly what happens in Alberto's second graph. But in his first graph, the data appears as smooth in the 900-1000 nm region as it appears in the 400-900 nm region. Just another reason not to use data-smoothing routines like boxcars. ;) Good job Alberto.


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 34 posts ]  Go to page Previous  1, 2, 3

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock