A new defect center in type Ib diamond inducing one phonon infrared absorption: The Y center

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The infrared spectra of 68 natural and synthetic diamonds with
detectable C centers at about 1130 cm(-1) and 1344 cm(-1) were recorded.
After correction and normalization of the spectra there was an attempt
to determine the A, B and C center nitrogen content of the samples using
the spectral fitting spreadsheet supplied by David Fisher from the DTC.
It became clear that for the majority of our samples the results were
erroneous for the C center content. In fact, the calculated C center
content based on the 1130 cm(-1) absorption was significantly higher
than what the 1344 cm(-1) absorption height indicated; in the fitted
traces proposed by the spreadsheet the 1344 cm(-1) absorption was always
at least 50\% higher than in the original spectrum. The overestimated C
center content and the residual trace after spectral fitting indicated
that some absorption bands were underlying the well-known,
single-substitutional nitrogen absorption at 1130 cm(-1). For this
reason all spectra were decomposed again by progressive subtraction of
the A, B, C and X center absorptions, in order to visualize any residual
absorption not attributed to any of those four, classically-recognized,
nitrogen-related one-phonon absorption systems. In the spectra of 38
diamonds the decomposition work resulted in a consistent residual
absorption feature with a relatively broad apparent maximum centered at
about 1145 to 1150 cm(-1). For the sake of convenience we use ``1145
cm(-1){''} to describe this feature. Two additional samples did not
exhibit any 1130 cm(-1) absorption but instead precisely the same
one-phonon absorption features as the newly-found residual. Consequently
several hundred nominally type Ib diamonds were screened by infrared
spectroscopy, and 22 had a one phonon absorption with a dominant 1145
cm(-1) absorption. This confirms that this absorption system was not an
artifact of the original spectral decomposition work. Further, this new
system is apparently a characteristic component of many natural type Ib
diamonds. Based on the fact that this newly described center is clearly
related to single substitutional nitrogen and that the last such
one-phonon IR absorption had been named ``X center{''} {[}1] (positively
charged single nitrogen), we propose to call this defect ``Y center{''}.
(C) 2011 Elsevier B.V. All rights reserved.