fluorescence and color

[slg47]

Hi everyone...I am not trying to rehash the "does blue fluor make my J/K look whiter" discussion but could not think of a more appropriate title.

In the GIA study it is stated that blue fluorescence in diamonds is due to a group of three nitrogen atoms (is this 3 nitrogens and a hole, instead of 4 tetrahedral carbons? or just 3 nitrogens...in some other arrangement?)

http://lgdl.gia.edu/pdfs/W97_fluoresce.pdf

but...I thought that diamond color, or yellowness, was also caused by the presence of nitrogen. so my question is...is a D with SBF really a D? I realize color is on a scale and the amounts of impurities are minute. I guess what I am asking is, is it possible to have enough nitrogen to cause SBF without causing perceptible difference in color (i.e. a D with SBF), or is something else responsible for either the fluor, color, or both?

apologies if this is not the correct forum but as a chemist (and nerd) I am interested in these things and this did not seem quite right for Rocky Talky. also if anyone has an article to link that would be great too.


ETA I just found this

Nitrogen can also occur in various ‘states’ with different electronic properties within a diamond so that it is possible for one D coloured non-fluorescent diamond to have 10 times more nitrogen than another that is K colour and fluorescent.

but am interested in what these different 'states' are?

 

[Garry H (Cut Nut)]

It's a bit hard to know where to start - but the simplest would be here Slg
http://en.wikipedia.org/wiki/Nitrogen-vacancy_center

Nitrogen is dispersed in Type I diamond when it grows into crystals (Type II has very little nitrogen and is very rare).
Over geologic time at high temp and pressure the unhappy nitrogen tends to congregate in the moleclues into N3 groups and then causes less absorption of the blue which causes the cape series D-Z yellowishness. This is also why almost all new man made HPHT synthetics are very yellow because the nitrogen is dispersed.

See if that helps you do some further web searching

 

[slg47]

Garry as always thanks for your expertise and input. I will definitely start there and will probably have more questions.

 

[yssie]

Hmm.. "states" maybe referring to substitution aggregates - groups of 2 Ns, 3 Ns, 4 Ns?

N3 centre is three nitrogens and one void substituting for a C tetrahedron, as you assumed. N3 + void complex has absorption beyond human vision (so doesn't contribute one way or another to colour), but paramagnetic - negative N3 (N2) centre absorbs at 478nm according to wiki - in the 'blue' range, result is faint yellow/brown if Type IaAB material

Articles -
def worth a read - makes it make sense - http://accreditedgemologists.org/lightingtaskforce/2010/2010presentation.ppt
basic outline - http://accreditedgemologists.org/lightingtaskforce/ExecSummary.pdf
if you're up for a meander you might tour this one http://www.nano.ir/papers/isi/224.pdf - I confess I quickly lost patience, but I do see that on pg5 it finally arrives at the conclusion that The spin of the ground state for N-V and N3 are 1 [26,27] and 1/2 [28] respectively - maybe you'll find it more useful!

 

[yssie]

well - I attempted more reading... I'll be very interested to hear a chemist's views on all this slg - my admittedly hazy memory of intro organic chem is definitely not up for this task!

 

[slg47]

Hmm.. "states" maybe referring to substitution aggregates - groups of 2 Ns, 3 Ns, 4 Ns?

N3 centre is three nitrogens and one void substituting for a C tetrahedron, as you assumed. N3 + void complex has absorption beyond human vision (so doesn't contribute one way or another to colour), but paramagnetic - negative N3 (N2) centre absorbs at 478nm according to wiki - in the 'blue' range, result is faint yellow/brown if Type IaAB material

Articles -
def worth a read - makes it make sense - http://accreditedgemologists.org/lightingtaskforce/2010/2010presentation.ppt
basic outline - http://accreditedgemologists.org/lightingtaskforce/ExecSummary.pdf
if you're up for a meander you might tour this one http://www.nano.ir/papers/isi/224.pdf - I confess I quickly lost patience, but I do see that on pg5 it finally arrives at the conclusion that The spin of the ground state for N-V and N3 are 1 [26,27] and 1/2 [28] respectively - maybe you'll find it more useful!

yssie...couldn't get the last one to open? just getting around to reading these, definitely not light reading material and things have been kinda stressful lately.

 

[yssie]

For the last one try plugging this into google search w/o quotes: Oscillator strength calculations in color centers of diamond and the role of spin

One of the links on the first page should be a pdf (it's the second link when I search google in firefox)



I've been following your other thread - I hope it works for both of you, it definitely sounds like a positive step