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 Post subject: Raman/PL results: Detecting HPHT treatment of type IIa Dia
PostPosted: Wed Sep 04, 2013 3:46 pm 
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HPHT (High Pressure High Temperature) treatment can be used to enhance the color grade of brownish or grayish type IIa diamonds to colorless or near colorless. Most of the larger HPHT-treated diamonds has been sold branded as GE-POL, Bellataire, Pegasus or Monarch and can be readily identified by laser inscription located on the girdle of the stone. Unfortunately it is possible to remove these laser markings by repolishing the girdle, and small stones may have entered the market without any inscription at all.
Photoluminescence spectroscopy is one of the very few methods available for determining HPHT treatment of colorless type IIa diamonds. However, this method can not be used alone without other instrumentation, because as a preliminary requirement, the sample under study has to be determined as natural type IIa diamond.


Image

About 2% of natural diamonds belong to type IIa, which by description do not have enough nitrogen impurities to be detected by FTIR (Fourier-Transform Infra Red) spectroscopy. This means about 98% of colorless to yellow (cape series) diamonds can be determined as natural and likely not HPHT treated by single or combination of following methods:

1.) Detecting the N3 absorption peak at 415 nm by optical spectroscope or spectrometer.
2.) Detecting IaA and/or IaB- type nitrogen defect peaks by FTIR spectroscopy.
3.) Observing lack of SWUV transparency by a screening device or UV-VIS-NIR spectrometer
If above tests indicate the sample is of type IIa it's origin may be one of the followings:

a) Natural untreated type IIa diamond
b) Natural HPHT color enhanced type IIa diamond
c) Synthetic type IIa diamond manufactured by HPHT process
d) Synthetic type IIa diamond manufactured by CVD process
There is no single tool capable of distinguishing all the possible origins of colorless IIa diamonds. A combination of multiple techniques is mandatory in order to achieve for reliable results. These include, but are not limited to: microscopic study of anomalous double refraction, deep UV fluorescence examination with DiamondView or similar devices, fluorescence microscope & spectrometer and photoluminescence studies at room temperature and in liquid nitrogen immersion with a sensitive Raman spectrometer such GemmoRaman-532.


Comparison of room temperature spectra

Looking at both treated and untreated samples in same figure reveals the differences in overall appearance of the spectra.

Image
HPHT-treated and untreated natural type IIa diamonds plotted on same graph for revealing the obvious differences in overall shape of the spectra. All the lines has been vertically shifted for visual convenience.

For full article read HERE

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Alberto & Mikko

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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Tue Sep 10, 2013 12:08 pm 
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=D> =D> Bravo! Excellent report! Thanks for making it available to all of us. :)

I had a number of questions after reading this report.
Some are answered here in this G&G article:
The Type Classification System of Diamonds and Why it's Important in Gemology

1. My first question concerns the ADR Tatami Strain pattern seen with crossed polars. Are type IIa diamonds the only ones which display this?
2. If one can see a 415nm absorption line with a hand held spectroscope, this positively indicates the diamond is not IIa.
How much nitrogen must be present in the lattice to detect that absorption with a hand held device like an OPL?
3. Are there any natural diamonds which exhibit stronger fluorescence in SWUV than LWUV?
4. It seems that both synthetic CVD and synthetic HTHP diamonds exhibit phosphorescence and natural diamonds do not. Can one use a standard SWUV light source to detect that?
5. It appears as though the severe cooling effect of liquid nitrogen is a great tool in separating treated HTHP diamonds from untreated diamonds. Presence of absorption at 637nm indicating treatment and a peak at around 558nm indicating no treatment. Why does extreme cooling cause this absorption to be more evident?

Thanks.


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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Tue Sep 10, 2013 3:31 pm 
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Wow. You guys collected spectra from 15 untreated type IIa. If these diamonds make up 2% of natural diamonds, then one would have to sort through and test (as described) well over 750 diamonds to find 15 type IIa. And considering that many type IIa would have already been selected for HPHT treatment, the number sorted must be even higher. What a heroic effort!


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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Tue Sep 10, 2013 3:49 pm 
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Thanks for interesting questions and link to the "Type Classification" article - That article is "classic" and definetely the number one article to refer.

Quote:
My first question concerns the ADR Tatami Strain pattern seen with crossed polars. Are type IIa diamonds the only ones which display this?


Type II diamonds are characterized by strong Tatami patterns, actually that pattern is very distinctive, and has not been observed in other type stones. Lack of nitrogen is the reason for the seeing the pattern, so both IIa and IIb stones may show it. However, there is some reports about very similar looking patterns, for example this type IaA brownish yellow nitrogen bearing CVD stone: http://www.gia.edu/gems-gemology/CVD-Gr ... Impurities

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If one can see a 415nm absorption line with a hand held spectroscope, this positively indicates the diamond is not IIa.
How much nitrogen must be present in the lattice to detect that absorption with a hand held device like an OPL?


For sure an hand held spectroscope is not enough “sensitive” to spot for a very weak 415 line for highest color grades, even digital spectrometer has some serious job for spotting it for D-E stones. Really can't say where the actual borderline for spectroscope is, but when it is seen the result is diagnostic... the stone contains N3 defects and thus belongs to Cape series = Ia type.

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Are there any natural diamonds which exhibit stronger fluorescence in SWUV than LWUV?


Not to my knowledge but with diamonds you never know…………

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It seems that both synthetic CVD and synthetic HTHP diamonds exhibit phosphorescence and natural diamonds do not. Can one use a standard SWUV light source to detect that?


Talking about colorless and blue stones, yes. A deuterium or xenon flash source are much more effective, but regular SWUV lamp works at least for HPHT synthetics in complete darkness. Very rarely natural diamonds may exhibit phosphorescence too, as the exceptional 4+ ct IIb stone you recently had a priviledge to examine. There is again a spectroscopic method for separating natural and synthetic IIb stones by further analysis of this fluorescence. Natural stones typically have a red component in fluorescence which is not present in synthetic stones.

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Why does extreme cooling cause this absorption to be more evident?


This is actually a perfect question for Dr. Brian? Cooling typically enhances both absorption and fluorescence effects for all materials. Or, should we say, it reduces the disturbing effects happening after the absorption or emission.... Basically, when there is less thermal vibrations in the crystal lattice the light transmitting trough it doesn't encounter as much "diffusive" situations where it's wavelenght broadens and/or shifts. OK, for explaining it well we need an native english physicist :D

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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Tue Sep 10, 2013 4:47 pm 
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I wrote:
It seems that both synthetic CVD and synthetic HTHP diamonds exhibit phosphorescence and natural diamonds do not. Can one use a standard SWUV light source to detect that?



Mikko wrote:
Talking about colorless and blue stones, yes. A deuterium or xenon flash source are much more effective, but regular SWUV lamp works at least for HPHT synthetics in complete darkness. Very rarely natural diamonds may exhibit phosphorescence too, as the exceptional 4+ ct IIb stone you recently had a priviledge to examine. There is again a spectroscopic method for separating natural and synthetic IIb stones by further analysis of this fluorescence. Natural stones typically have a red component in fluorescence which is not present in synthetic stones.


:oops: Oh good grief; how quickly things are forgotten. I was sitting in a dark room with that 4.32 carat, emerald-cut diamond every chance I got.
I need to rethink my.....uh.....thoughts.


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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Tue Sep 10, 2013 11:57 pm 
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mikko wrote:
Quote:
Why does extreme cooling cause this absorption to be more evident?


This is actually a perfect question for Dr. Brian? Cooling typically enhances both absorption and fluorescence effects for all materials. Or, should we say, it reduces the disturbing effects happening after the absorption or emission.... Basically, when there is less thermal vibrations in the crystal lattice the light transmitting trough it doesn't encounter as much "diffusive" situations where it's wavelenght broadens and/or shifts. OK, for explaining it well we need an native english physicist :D


What a cool question (pun intended :-D ) Mikko explained well what is happening. So I'll just try to explain why it happens.

A narrow (few nm) fluorescence peak seen in a spectrum arises from light emitted by particular ions in the crystal structure. The exact wavelength that one ion emits light is sensitive to its local environment. If the neighbors are a bit closer or a bit further away, then the wavelength of the emitted light will be shifted one way or the other. Since all the atoms and ions are vibrating in place, the environment around the ion is always changing, and so light emission is spread across a range of wavelengths.

Temperature is a measure of the amount of vibrations going on in the crystal. Lowering temperature reduces vibrations, which reduces changes in the environment around the ion. In turn, this reduces the range, or width, of emitted light wavelengths.

Now the rate at which ions emit light is proportional to the area of the fluorescence peak, where area equals width time height. Roughly speaking, this rate doesn't change when temperature is lowered, and so the area of the peak doesn't change. If peak area stays the same, but lower temperature reduces peak width, then peak height has to increase.

So this is why cooling the crystal leads to taller, narrower, easier-to-see peaks.


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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Wed Sep 11, 2013 5:09 am 
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Excellent! Keep up the good work guys! =D>


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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Wed Sep 11, 2013 10:04 am 
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Related sidebar.
Recently on GemA mailtalk there has been a discussion about a a UV pen called Diamapen.
It allegedly can separate Type IIa diamonds from those which are not.
There seems to be a lot of confusion as to exactly how this "pen" accomplishes the task....
It would have to use SWUV right?
Any insight?


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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Wed Sep 11, 2013 10:14 am 
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For what i know,
the DiamaPen is nothing but a 5 mW 405 nm laser pointer. I didn't tested it personally so i cannot provide for a direct description but it seems it's actually very useful in order to excite fluorescence reactions in many stones, actually one of the best seller stuff in our industry. But remains something you can purchase for 5 $ orso on fleabay AND it has nothing to do with SWUV. we have pratically completed to work on a GemmoRaman accessory quite similar to the SSEF diamond spotter but more compact since it uses a REAL SWUV led. Those leds are unfortunately still really expensive and, despite the virtual offer on the market, few products are REALLY consistent with the claimed features........they cost a fortune, far more than the 199$ asked for the DiamaPen.......... :wink:


ciao
albé

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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Wed Sep 11, 2013 10:24 am 
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If the Diampen is a 405nm laser pointer ( :shock: ) how could it possibly identify diamond type?

Oh, a new SW addition for the GemmoRaman......interesting, very very interesting......


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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Wed Sep 11, 2013 10:27 am 
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Barbra Voltaire wrote:
If the Diampen is a 405nm laser pointer ( :shock: ) how could it possibly identify diamond type?


it can't.

Quote:
Oh, a new SW addition for the GemmoRaman......interesting, very very interesting......


prototypes are working since a couple of months now, everything is ok, we hope to be on air very soon... :wink:


ciao
albé

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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Wed Sep 11, 2013 10:41 am 
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ha! The cat's out of the bag now Alberto.


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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Wed Sep 11, 2013 10:55 am 
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Brian wrote:
ha! The cat's out of the bag now Alberto.


he! Brian!! :)

ok, a small preview.............just for you and the rest of GO gang 8)

Image

Ta-daaaaaaaa!!!! :D
let me introduce the DiaGuard!!! 8)

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 Post subject: Re: Raman/PL results: Detecting HPHT treatment of type IIa D
PostPosted: Wed Sep 11, 2013 12:12 pm 
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Start giving the Raman units away for free and make a killing on the accessories... Worked for the angrybirds bunch... ;)


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