Specific spectroscopic features of yellow cuboid diamonds from placers in the north-eastern Siberian Platform

Abstract

A series of yellow cuboid diamonds from alluvial placers in the north-eastern Siberian platform have been examined with Fourier-transform infrared (FTIR) absorption spectroscopy, photoluminescence (PL) and electron paramagnetic resonance (EPR). All crystals having characteristic FTIR spectra with predominantly C and A centres belong to mixed type IaA/Ib with small total nitrogen content (up to 330 ppm). PL is characterized by many bands with two bands related to the NV 0 and NVcentres common to all the samples. The FTIR spectra are also characterized by deformation-induced 'amber' centers. Some of the yellow diamonds studied show new bands at 4272, 4548, and 5960 cm -1 instead of the bands at 4060 and 4170 cm -1 common for 'amber' centres. An EPR study has revealed the presence of OK1 centres associated with titanium impurity. The plastic deformation of the studied diamonds is expressed as a 'tatami' strain pattern in the features of their internal structure.

IR Spectroscopy of Vacancy Clusters (Amber Centers) in CVD Diamonds Nanostructured by Fast Neutron Irradiation

“…The changes in the IR absorption spectra after annealing at temperatures above 1000 • C for samples D1 and D3 are shown in Figure 3a,b, respectively. The AC 4100 cm −1 absorption coefficient reaches α = 15 cm −1 for sample D3, which is an order of magnitude higher compared to that for the maximum AC absorption reported for natural diamonds [23][24][25][26][27][28][29][30][31][32][33]. The AC absorption for sample D1 is about three times lower than for D3; this ratio roughly corresponds with the neutron fluence ratio.…”

“…For the sample D3, the 4100 cm −1 band magnitude exceeds that for the two-phonon band (Figure 1b). Based on the 4100 cm −1 band position, shape and evolution with annealing, it can be associated with AC defects [23][24][25][26][27][28][29][30][31][32][33]55]. In the virgin unirradiated samples, CH x bands (2800-3000 cm −1 ) of the bonded hydrogen, presumably located at the grain boundaries, are detected (see bottom spectrum in Figure 1a), as well as a structureless absorption due to the inclusion of amorphous carbon.…”

“…The high-frequency shift in the 4100 cm −1 band position with T an occurs due to the relative amplification of the 4112 cm −1 component. These two components are well-known for diamonds with ACs [23][24][25][26][27][28][29][30][31][32][33].…”

“…The absorption coefficients of AC bands commonly do not exceed a few tenths of cm −1 [23][24][25]29], which causes difficulties in the optical absorption measurement in thin layers. An additional problem is the inhomogeneous color of natural diamonds, as well as the sectorial distribution of impurities and defects over their volume [30][31][32][33].…”