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 Post subject: Help please!
PostPosted: Mon Dec 09, 2013 10:49 pm 
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Hello, I am new to this forum!

I am a student studying forensic science at University of Kent, Canterbury, England and am in my final year, as part of my final year I have to do a project from a list we were provided with.

I chose to do a project on analysing gem stones using Raman spectroscopy. So far it has generally gone well and have been receiving lovely spectra of diamonds, cubic zirconia, ruby and sapphire, however...Emerald has decided that it hates me and is proving a little challenging (as to be expected from the research I have done) and I was just wondering if anybody has got any advice on the best method of gaining a decent spectrum with minimal fluorescence.

Any advice or suggestions would be greatly appreciated,
Thank you!
Jenny :)


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 Post subject: Re: Help please!
PostPosted: Mon Dec 09, 2013 11:58 pm 
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This might be a dumb answer, but at least under SW/LW UV not all emeralds are fluorescent. If you select a vanadian emerald or one rich in iron rather than a purely chromian emerald you might have more luck. That might be a way of side-stepping the issue, anyway (though of course the purest chromian emeralds get all the press). That said, there are people here who know a lot more than me (especially about the specifics of Raman spectroscopy, about which I know next to nothing) who will hopefully chime in.

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 Post subject: Re: Help please!
PostPosted: Tue Dec 10, 2013 4:05 am 
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Hi and welcome to the forum!!!

I would love to know more about your setup before to say something, which excitation source are you using?

ciao
alberto

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 Post subject: Re: Help please!
PostPosted: Tue Dec 10, 2013 7:07 am 
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I am using the standard lasers used in most raman spectrometers as an excitation source and have tried blue (445nm), red (635nm) and near infra red (785nm) and all of them have produced bad spectra with a tonne of fluorescence.

My supervisor has not done this project before and although he obviously knows a lot about raman he does not specifically know a lot about emeralds and raman other than everywhere saying they fluoresce a lot , we are both conducting research into getting around the problem and I came across this forum haha

Jenny


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 Post subject: Re: Help please!
PostPosted: Tue Dec 10, 2013 7:08 am 
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Oh and thank you guys for replying :) any help is greatly appreciated!


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 Post subject: Re: Help please!
PostPosted: Tue Dec 10, 2013 9:28 am 
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ok, i would avoid visible lasers for taking Raman fingerprint of emeralds, 785 nm should work. I really find weird you have problems with emeralds and at the same time was able to take a ruby fingerprint....... :roll: :roll: :roll:

ciao
alberto

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 Post subject: Re: Help please!
PostPosted: Tue Dec 10, 2013 10:16 am 
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Yeah I find it weird too :/ gonna just have to keep going at it I guess or try to get hold of a different emerald

Thanks for your help!


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 Post subject: Re: Help please!
PostPosted: Tue Dec 10, 2013 10:16 am 
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Would an iron rich ruby still cause fluorescence problems with a Raman? If it's the chromium content that's at the root of the issue, maybe the suggestion of a Vanadium emerald isn't a bad solution. Alberto, oh wise Raman expert?


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 Post subject: Re: Help please!
PostPosted: Tue Dec 10, 2013 11:17 am 
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hola Julie

Julie Gowans-Poli wrote:
Would an iron rich ruby still cause fluorescence problems with a Raman? If it's the chromium content that's at the root of the issue, maybe the suggestion of a Vanadium emerald isn't a bad solution.


the Raman scattering is so weak that even a very slight luminescence reaction may cause a complete saturation of the signal. truth to be said we were very rarely successful in taking Raman fingerprints of sapphires since almost every time the luminescence peaks of chromium prevented a decent readout. that said, a Vanadium emerald would be ok but, well, even the slightest amount of chromium can mess up the situation..........
however, i never had troubles atall with emeralds by using 785 nm, i was able to take many perfect readings of every emerald type.......actually we tested many of them searching for diagnostic peaks of natural and synthetic fillers......... :roll: :roll: :roll:

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Alberto, oh wise Raman expert?


ok, i'm only the wise marketing manager, the Raman expert lives in the far north.... :lol:

ciao
albé

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