Comparison of gemological and spectroscopic features in type IIa and Ia natural pink diamonds

Abstract

The majority of natural pink diamonds have a color origin due to absorption from a broad 550 nm band that has been associated with plastic deformation. One consistent feature in the photoluminescence spectra of these pink diamonds is a wide emission band extending from ~600 to 750 nm, with a series of smaller oscillations overlaid on the larger emission band. This “pink emission band” is seen in diamonds colored by the 550 nm absorption band; the absorption band often, but not always, shows similar oscillations at ~600 nm (called the 609 nm system by previous researchers). This emission band served as a proxy for the 550 nm absorption band as we performed spatial mapping to chronicle the differences between the uniform coloration in type IIa pink diamonds and the pronounced banding in type Ia pink diamonds. We also used Raman spectroscopy to identify the internal crystal inclusions present in type IIa pink diamonds and determined that the majority have a sub-lithospheric origin.