New Mineral Named After GIA’s John Koivula
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 Post subject: diamond
PostPosted: Fri Jun 01, 2007 2:49 pm 
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I'd thought I'd make a diamond research thread to encourage Jean Marie to post some of his spectra and tell us more about the diamonds he is investigating.

The diamond here comes from the mineral collection. It is perfectly set up for a transmission spectrum, thin with flat, parallel surfaces (cleavage planes?). In other words, this diamond is basically one big "window", gemologically speaking.

In contrast a diamond cut for an engagement ring would be almost useless for direct transmission measurement, because of TIR. I'm guessing that this is why Jean Marie is collecting %T via a reflection method.

This diamond is unpolished, but has nice flat surfaces. To my untrained eyes, it is pretty much colorless and transparent. I didn't take a loupe to look at inclusions. And that's all I know about it. Anyways this was a very easy spectrum to collect, about 10 seconds total collection time to ensure good statistics.

mineral box 007
diamond
location: South Africa
mass: 0.10 g

Note that the bottom of the vertical scale for all these spectra is set at 20%, not 0%.

Here is the VIS+IR spectrum (click for larger image):
Image

In the IR, we can see a small dip around 791 nm, and a small peak(?) around 801 nm. The entire region from 550 nm to 850 nm seems to be the bottom of a wide, wide absorption band.

Here is the visible spectrum:
Image

A very shallow dip can be seen at 479 nm. The very deep absorption line occurs at 416 nm. Another definite absorption line occurs at 404 nm.

Usually, I don't show spectral features below 400 nm (in the UV) because the light signal is dropping rapidly. But this diamond has a lot going on in the region around 400 nm, so I decided here to post an extra picture showing the blue-to-UV range. The decreasing light in the UV causes the noisier statistics in that range.

Here is the UV + visible blue spectrum:
Image


Last edited by Brian on Tue Jun 05, 2007 4:26 pm, edited 1 time in total.

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PostPosted: Tue Jun 05, 2007 11:04 am 
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Oh.. 8) cool.
Brian open a post on diamond.

Yes I am interested to learn more about diamond spectroscopy.
But you have to know that I am a true beginner.
At this time I have big difficulties to assign correclty and/or understand spectroscopic feature from one diamond to an other.

In the Brian spectrum, what it is very clear is the N3 center (three atom Nitrogen around a carbon vacancy) at 415 nm.
We can found this typical feature in a lot of diamonds.

Brian, have you collected your spectrum at the liquid nitrogen (77K) temperature?
Because more your are dow in T more the peack definition /resolution is hight.
(Iwill post here an exemple)

The peack at 791 nm is very intrigant for me (at this time ;-) ).
If I well remember I have a spectrum of "colorless" (i.e. colorless to very light brown or yellow) with this feature at 791nm...
I willm check my spectrum database to post it here.

What I have learn from bibliography and other discutions is :
when we have a specific diamond to study it is necessary to do FTIR spectrum to determine the exact diamond type.
e.g. IaA, IaB, IaA>>B, IaB>A, Ib, IIa, IIb, etc.....
because a specific feature at xxx nm in a type IaA have not the same signication in a Ib type Ib ..etc.

I think, we have to know in this "diamond research thread" that studying colored diamond only with a "litle" spectrometer (even at 77K) without FTIR approch can be a source of confusion and/or errors.

Nevertheless I think that Vis-NIR spectrometry can be a powerfull tool to start to have assumption on the origin of a diamond color (i.e. treated or not, synthetic..etc.).
And some time spectrometry will be conclusive with the help of other gemmological caracteristic (fluorescence, inclusions, magnetism, etc.).

:arrow: In all the cases, and because diamond fiel is very complicated, confirmation must be done by an equiped and skilled lab !


Now, what do you think to start our "funny stuff research" on the 791 nm :P peack?

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Last edited by Gemça on Tue Jun 05, 2007 4:14 pm, edited 1 time in total.

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PostPosted: Tue Jun 05, 2007 1:23 pm 
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hi Jean Marie

Sadly, the spectrum was collected at room temp, 300 K. Still, nice to know why the 415 nm absorption appears. Even if these are only "toy" spectra.

I will think about the little feature at 791 nm. Do you think it is associated with the carbon crystal, or do you think it arises from some impurity like the nitrogen absorption? I doubt that the feature is an experimental artifact, because the light source is well-behaved through that range.

Since I didn't know what to expect, I wasn't too surprised to see a dip in the IR. But I was surprised to see it followed almost immediately by a rise. As I find time, I'll go back and focus on that region. I have another small diamond that maybe I can try too.

Sadly, classes and my lab have started back up, so I don't know when I can squeeze it in. But eventually....


Last edited by Brian on Tue Jun 05, 2007 4:29 pm, edited 1 time in total.

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PostPosted: Tue Jun 05, 2007 4:13 pm 
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Hi Brian,

For information, Right now from my home PC, I can not see your spectrum in your post (may be a problem on imageshack server?)..

Whatever,

Concerningthe peack at 741 nm( and if I am not wrong) it is typical of the GR1 center (GR for "Genaral Radiation": an isolated neutral carbone vacancy V0) This peack can be present after irradiation (natural and/or artificial).

In other hand,
I have wrote:
If I well remember I have a spectrum of "colorless" (i.e. colorless to very light brown or yellow) with this feature at 791nm...

I was wrong..my mystery pic is at 904 nm in a orange diamond.
Sorry for the mistake.

Since I have not analysed a lot of diamond, I have not a big knowledge of what I can expect.
But I have never see this feature at 791 in a diamond at this date.
In the Zaitsev's book "Optical Propertie of Diamond" a natural occuring center is described at 793.5 nm in the diamond containing S2 and S3 center.... but what is the S2 and S3..

In your spectrum you have the N3 center (415 nm typical of "cape serie").
Note: You have equally the 478 nm feature that is the N2 center (N2 is another excited state of the N3 center in his energy gap).

So you have N3 and N2 peack.. we can tell ...:roll: hummm.... you have a diamond :P with nitrogen impurity (probably as A and/or B agregate).. so your diamond it is not of the typa IIa (without nitrogen).. thus this diamond was probably not exposed to a GEPOL process (HPHT treatment on brown type IIa diamond to henance it to colorless) :)
But this is just supposition... :wink:

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PostPosted: Tue Jun 05, 2007 4:40 pm 
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hi Jean Marie

I made an error in the previous post, there is nothing at 741 nm... I meant 791 nm. And for some reason, imageshack was mis-behaving... I re-loaded the spectra, so that they should come up now.

Perhaps the dip at 791 nm is this S2 or S3 center. Maybe S refers to sulfur?

I'm pretty sure this diamond is natural with no treatment whatsoever to enhance its color. :lol: If you saw this lying on the street, your first reaction would be to think it was a fragment of glass.

What causes the absorption at 404 nm?


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PostPosted: Tue Jun 05, 2007 11:39 pm 
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404?, or 415nm the latter being a very regular feature.


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PostPosted: Tue Jun 05, 2007 11:48 pm 
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If you look in the UV-visible blue spectrum, there is a distinct dip along the downward slope at 404 nm. Sure, the 415 nm is a huge dip, but the absorption dip at the 404 nm is more distinct than the one at 478 nm.

Jean-Marie keeps pointing out spectral features one nm less than my readings from the graph... maybe I need to calibrate the spectrometer? Oh well, as I've said before, whats a nanometer among friends?


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PostPosted: Wed Jun 06, 2007 3:53 am 
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Since we have a resolution at 1.5 nm to 3 nm with our "toy spectrometer" we can have (I think) some variations.
Moreover, I wonder if peack's deplacement is variable with the temperature.
The bibliography give N3 at 415nm, N2 at 478, etc.. but generaly at 77K

I dont know what are the S centers and if S is for Sulfur.. may be :roll:
I have searched on google but without result :?

Concerning the 404 nm peack I don't know.. and I am being wary in this spectral zone because of the big signal noises..
But we can note that the spectrum continum start to absorb the UV region.

I continue to search arround the 791 center you have seen in your diamond :)

In other hand I am curious to know what is the center at 904 nm that I have seen in a orange (probably natural) diamond.

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PostPosted: Wed Jun 06, 2007 6:39 pm 
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a google book reference on S3 centers in diamonds. It is pretty annoying that the book reference cuts off just at the interesting bit. :evil:

another google book reference, you need to scroll down a few pages to find the S3 reference in this one.


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PostPosted: Thu Jun 07, 2007 3:25 am 
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I have the first book from Zaitsev (Optica propertis..). But it is very difficult to read for a newbees like me.
I have to search more closy in this book to try to find somthing on the S2, S3 center.... :)
Thank you for the link 8)

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 Post subject: Re: diamond
PostPosted: Wed May 25, 2011 11:49 am 
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i wanna share, just for fun, some polished diamonds trasmission spectras i took with my new setup (which is very far to be completed)
here we go:

Image

you can see the 3 spectras in one shot, both the 415 Nm and 478 Nm features are clearly visible.
i was able to avoid the TIR issue by using a custom arranged integrating sphere setup.
the unit is an Ocean Optics HR4000.
well, It's a starting point, but it seems fun! 8)
ciao
alberto

Sidenote: the above spectras characteristics are not what pictured in the spectrasuite panel, i used 4 scans to average and 6 of boxcar width

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 Post subject: Re: diamond
PostPosted: Wed May 25, 2011 12:06 pm 
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=D>

finalmente arrivato? Kewl... Enjoy!


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 Post subject: Re: diamond
PostPosted: Wed May 25, 2011 9:25 pm 
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just as Tim says... "finalmente!" :smt111

Nice spectra!

But I do have a couple of suggestions...

I suggest not using boxcar, setting it to zero. It reduces effective resolution and it can turn a single "hot pixel" (which you know to ignore) into a misleading peak structure.

Also, I suggest you try averaging 30 scans. Marty Haske reckons a 31-scan average is best. Interesting that we both came to essentially the same conclusion independently.

The upshot is, what you want boxcar to do is usually better done by averaging more scans.

Looking forward to your first colored gemstone spectrum!


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 Post subject: Re: diamond
PostPosted: Thu May 26, 2011 3:03 am 
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Yeah, Finalmente, thank you to both of you! :D

Brian wrote:
But I do have a couple of suggestions...

I suggest not using boxcar, setting it to zero. It reduces effective resolution and it can turn a single "hot pixel" (which you know to ignore) into a misleading peak structure.

Also, I suggest you try averaging 30 scans. Marty Haske reckons a 31-scan average is best. Interesting that we both came to essentially the same conclusion independently.


Thank you Brian, i've started to play with it only recently and actually i'm involved in other projects so i don't have so much time, i'm aware about boxcar and average scans issues (i tohught 20 could be enough, though, so thank you :D ). now i have to focus more on lightsources in order to use the HR at best of it's possibilities and in the widest wavelenght spectrum..... suggestions & advices would be really appreciated!! :mrgreen:

Quote:
The upshot is, what you want boxcar to do is usually better done by averaging more scans.


yups!

ciao
albé

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 Post subject: Re: diamond
PostPosted: Thu May 26, 2011 2:08 pm 
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Hey Congratulation Alberto. It's been a long wait,

I'm glad you've finally got it set up and started to play 8)


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