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 Post subject: HPHT Diamond Testers using Phosphorescence: Unreliable?
PostPosted: Sun Sep 30, 2018 9:48 pm 
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Dr. Hiroshi Fitawaki, FGA, Kentaro Emori and Keiji, Koida of the Central Gem Laboratory, Tokyo, Japan wrote:
An article in the latest Journal of Gemmology Volume 36/No.3/2018), entitled "Reduced Phosphorescence of Type II HPHT- Grown Synthetic Diamonds After Electron Beam Irradiation" reports on a study of the effects of irradiating HPHT melee-size diamonds with various levels of irradiation with an electron beam.

Since both, reactions to SWUV and Phosphorescence are relied upon as indicators in identifying HPHT synthetics by several gadgets marketed as Synthetic HPHT Diamond detectors, this article casts a shadow on their reliability.

If HPHT synthetic diamond melee are exposed to a large dose of electron-beam radiation (100.0 x 1015 electrons/cm 2) it essentially eliminates or significantly quenches both fluorescence and phosphorescence.
Image

In addition, increasing the dose of electrons increased a blue coloration of the synthetics.
The synthetics which totally lost their phosphorescence gained the most blue. Unfortunately, this blue tone can not be seen when the stones are mounted.
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 Post subject: Re: HPHT Diamond Testers using Phosphorescence: Unreliable?
PostPosted: Wed Oct 03, 2018 5:00 am 
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thx Barbra for posting that.
this is one of the reasons why its very dangerous to rely on a specific feature of synthetic material to make a call and its even more dangerous to rely on them only when developing a screening techinque. We all know phosphorescence is one of the main one for recent HPHT melee production due to boron doping (many of those stones are actually ideintified as type IIb by FTIR). Besides this interesting experiment which could became a rather cheap practice for quenching phosphorescence to fool screening units based on that feature (melee can be irradiated in large batches), growning methods and dopants can change over the time. I think that the only way a screening system could work safely is to rely on features of natural diamonds which cannot be replicated in synthetics, again the concept should be: identification of the naturals AND refer for further testing for the others. :wink:

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 Post subject: Re: HPHT Diamond Testers using Phosphorescence: Unreliable?
PostPosted: Mon Dec 03, 2018 6:11 pm 
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Electron beam bombardment would cause a significant increase in lattice strain in these diamonds which would only provide a clue that such a process was used on a synthetic and not a verification.

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 Post subject: Re: HPHT Diamond Testers using Phosphorescence: Unreliable?
PostPosted: Mon Dec 03, 2018 10:53 pm 
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The main issue is separating natural from synthetic and the reliability of instruments that claim to be able to do it.
:smt112


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