Abstract Gems & Gemology, Spring 2013, Vol. 49, No. 1

A New Defect Center in Type Ib Diamond Inducing One Phonon Infrared Absorption: The Y Center

This paper describes the discovery of a new defect center in natural and synthetic type Ib diamonds: the Y center. Sixty-eight natural and synthetic diamonds with detectable C centers, ranging from 0.01 to 1.34 ct and representing common colors for type Ib diamonds (various hues of yellow, orange, brown, and “olive”) were studied.

The other color centers traditionally responsible for one-phonon absorption (i.e., spectral absorption due to the presence of certain defects in the diamond’s lattice structure) include single isolated boron, the A center (di-nitrogen), the B center (four nitrogen atoms surrounding an atomic vacancy in the diamond lattice), the C center (single-substitutional nitrogen, N0), the X center (positively charged single-substitutional nitrogen, N+), and the D, E, and F centers, which have not been attributed to any specific defect.

After correction and normalization of the samples’ infrared spectra, and an attempt to determine the A, B, and C center nitrogen content using spectral fitting data, the researchers found that the margin of error for the C center content was at least 50%. This suggests that some absorption bands underlie the well-known single-substitutional nitrogen absorption at 1130 cm–1. For this reason, all spectra are decomposed again by progressive subtraction of the A, B, C, and X center absorptions. For 38 diamonds, this resulted in a consistent residual absorption with a relatively broad apparent maximum centered at ~1145 cm–1.

A large sample of type Ib diamonds confirmed that this new absorption system is not an artifact of the original spectral decomposition work. The authors propose to call it the Y center because it is clearly related to the single-substitutional nitrogen system of the last named one-phonon infrared absorption center, the X center.

Abstracted by Edward R. Blomgren