Nitrogen in diamonds?

I was wondering what it means if someone says that a type 2a diamond is nitrogen free?
Does this mean that you can measure it? How? and is this a part of certification? Does it mean the diamond is of a better quality?

I hope someone can hep me?

Kind regards,

Henri Human

Type I diamonds have nitrogen that can be dispersed through out the stone replacing a carbon atom. This absorbs some blue light and is why most diamonds are in the 'cape' or slightly yellow series.
If diamond has been formed and held at high pressure and temp for millions of years the nitrogen can migrate and join up into little clusters of 3's. This stops it absorbing blue light, and is why 'D' color is possible.
Man made synthectic diamond is almost always yellow because the nitrogen wand other impurities are dispersed through out the lattice.
garry

Garry Holloway FGAA DipDT

HCA and Ideal-scope developer

http://www.ideal-scope.com and
http://www.HollowayDiamonds.com.au

Also note this part as it refers to the use of type IIa diamonds in HPHT treated diamonds:

The two pear brilliant diamonds submitted for grading were of different types; the heavier E-colour diamond is of Type Ia whereas the rarer colour (D-colour grade) stone belongs to the Type IIa sub- group. The retailer jeweller may at this point be asking what this discussion of diamond types has to do with him? He may think the two diamonds are well matched so their ‘type’ is not important to him. But the jeweller should recall that almost all the diamonds suitable for the high pressure-high temperature (HPHT) diamond treatment designed to remove the brown component thus improve the colour grade, are of Type IIa. This form of treatment, as carried out by GE POL has been discussed in previous GemLab columns. It is paramount that gemmologists can identify and further study Type II a diamonds. In our laboratory we use infra- red spectroscopy to routinely screen all colourless diamonds submitted for testing and grading; Type IIa diamonds yield a different i-r spectrum compared with the spectra of the other diamond types. Of the GE POL treated diamonds examined by researchers, the vast majority are type IIa and are of very good colour and clarity grades. The number of such treated diamonds represents a tiny fraction of all polished diamonds in the global market. Once a good quality colourless Type IIa diamond is identified, further work is needed to establish whether it is a HPHT treated stone. Researchers have found that any pale yellow coloration in such treated diamonds is due to very low concentrations of single nitrogen, not detected in untreated Type IIa diamonds. Using laser- excited photoluminescence spectroscopy at low temperatures may reveal two luminescence peaks in the spectrum. The ratio of the intensities of these peaks may offer one method of identifying HPHT treated diamonds.

However, once the diamonds have been screened by cheap and easy testing, if one needs to know more, then the fancy IR Spectroscope comes into play, but unless you are a scientist or work in a very world class lab, it is far from an essential tool for most gemologists at the present time. Maybe it will become a less costly tool and the need may grow to have them in normal gem labs. Time will tell.

It is my understanding that IIA diamonds are not absolutely nitrogen free. This has been said to be a simplistic description but not exactly the case.
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David Atlas
Accredited Gem Appraisers

David S. Atlas

GG(GIA), ASG, Sr. Mbr. NAJA

www.datlas.com

Check out these links:
Diamond Types I/II ab, www.gemguide.com/news/archives1.htm

and
www.precious-stonelab.co.uk/Diamond%20Types.htm

In particular:

quote:

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In 1959 it was established that the majority (over 99%) of natural diamonds contain sub-microscopic nitrogen as an impurity within the carbon pattern. Such diamonds are termed ‘Type I’. Those diamonds which do not contain readily detectable nitrogen as an impurity are termed Type II.

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Type II diamonds

These rare diamonds allow the passage of SWUV light and do not contain readily detectable nitrogen hence the Type II diamond atomic structure is more theoretically perfect than that of Type I diamond. As with Type I, Type II diamonds are sub divided. Some Type II diamonds conduct electricity and are termed Type IIb. They contain boron and mostly all are blue in colour. Type II diamonds lacking the impurity boron are termed Type IIa; they have the most perfect crystal structure thus are extremely transparent, often of excellent gem colour i.e. colourless, and have the greatest thermal conductivity. Type II crystals tend to be large and irregular in shape. A number of large famous diamonds, such as the Cullinan and the Koh-i-Noor diamonds, are of type IIa.

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