Lab Notes Gems & Gemology, Spring 2013, Vol. 49, No. 1

Diamond with Extremely Strong 578.9 nm Emission Center

Wuyi Wang

Download PDF
Light Blue Type IIb Diamond
Figure 1. This 4.72 ct Light blue type IIb diamond displayed some of the strongest dislocations ever observed in natural diamonds by GIA. This resulted in a hazy impression and a lower transparency than other type IIb diamonds. Photo by Jian Xin (Jae) Liao.
Photoluminescence analysis at liquid-nitrogen temperatures and varying laser excitations has become increasingly important in diamond color origin testing. The 578.9 nm emission normally occurs with many other emission lines, and it is usually weak in natural type IIa and IIb diamonds. Meanwhile, the physical model of this optical center is unclear. The New York laboratory tested a very rare diamond that showed extremely strong 578.9 nm emission.

This 4.72 ct rectangular diamond (9.75 × 8.90 × 5.92 mm) had a color grade of Light blue and an even color distribution (figure 1). Infrared absorption spectroscopy analysis identified it as a type IIb diamond with a boron concentration of about 16 ppb. This stone showed very strong dislocations, resulting in a hazy impression and a lower degree of transparency than most type IIb diamonds. Microscopic observation revealed very strong linear graining and related high interference colors. The intensity of the dislocations was among the strongest ever observed in natural diamonds at a GIA laboratory.

The outstanding feature of this diamond was the extremely strong emission at 578.9 nm, with possible side bands at 586 and 593 nm (figure 2). No other emission line was detected in the visible light region, which is very unusual for a natural type IIa or IIb diamond. This feature was confirmed with 457 and 488 nm laser excitations. The exclusive occurrence of the 578.9 nm emission and the very strong lattice dislocations suggested that this emission was a dislocation-related optical center.

Visable Range Spectrum Light Blue Type IIb Diamond
Figure 2. The diamond showed extremely strong emission at 578.9 nm and its possible side bands at 586 and 593 nm. The exclusive occurrence of the 578.9 nm emission and the very strong lattice dislocations in this diamond suggested that the emission was a dislocation-related optical center.