This report delves into the intricate characteristics of a peculiar yellow-green diamond, exploring the scientific methods used to understand its unique color zoning and micro-inclusions.

Beyond Brilliance: The Hidden Worlds Within a Starburst Diamond

Initial Observations: A Diamond's Unique Cloud Formations

A recent analysis at the Carlsbad laboratory focused on a 2.50-carat, faint yellow-green round brilliant diamond. What immediately drew attention were several yellow regions, randomly distributed and composed of stacked cloud-like structures. These clouds presented a distinctive four-sided star pattern, particularly noticeable near the diamond's girdle. Closer inspection revealed these clouds to be aggregates of micro-inclusions, with the central part of each cloud showing a cross-shaped arrangement of more intensely colored particles. When observed from a different angle, these same cloud formations transformed, appearing as a sequence of overlapping, bright yellow triangular shapes. The remarkable and unusual nature of these formations prompted a thorough scientific inquiry.

Fluorescence and Spectroscopic Analysis: Uncovering Internal Properties

Under long-wave (365 nm) UV radiation, the diamond's main body exhibited a blue fluorescence. Utilizing a deep-UV imaging microscope (operating at wavelengths below 230 nm), researchers were able to precisely identify that the distinct cloud patches displayed a subtle yellow fluorescence. The diamond's absorption spectrum, spanning ultraviolet, visible, and near-infrared wavelengths, indicated significant absorption features at 415 nm (attributable to the N3 center) and 478 nm (associated with the N2 center). Additionally, broad absorption bands centered around 730 nm and 836 nm, alongside a peak at 563 nm, provided strong evidence for the presence of hydrogen-related defects. Infrared absorption analysis further categorized the diamond as type Ia, notable for its high concentrations of both nitrogen and hydrogen.

Deciphering Color Origins: The Role of Defects and Nitrogen

While hydrogen-related defects can contribute to brownish or greenish hues in a diamond's overall color, they are not considered the source of the vivid yellow color zones observed in this particular specimen. Typically, yellow coloration in diamonds is linked to cape defects, H3 defects, isolated nitrogen atoms (C-centers), or a specific absorption band at 480 nm. However, when considering localized, patchy yellow zones, the influence of C-centers or the 480 nm absorption band is more commonly cited. This distinction was crucial for understanding the unique characteristics of the diamond under investigation.

Photoluminescence Insights: Pinpointing the Yellow Color Source

Photoluminescence (PL) spectra were meticulously recorded from both the bright yellow color zones and their surrounding areas. Notably, neither the H3 center (identified by a peak at 503.2 nm) nor the characteristic PL features associated with the 480 nm absorption band were detected. This crucial finding suggested that these common causes were not responsible for the yellow color zones in this diamond. Instead, the NV– center, which typically appears at 637 nm and is a hallmark of diamonds colored by isolated nitrogen, was exclusively found within the bright yellow zones. This strongly implies that the yellow color originated from the presence of C-centers, confined to specific regions near the diamond's surface.

Unresolved Mysteries and the Power of Advanced Techniques

Previous research has documented instances of yellow overgrowth layers forming on near-colorless diamonds during later stages of growth. However, the precise composition and formation mechanism of the micro-inclusion clouds that coincide with the yellow color zones in this particular diamond remain largely unexplained and warrant further investigation. This extraordinary diamond, with its distinct starburst-patterned clouds and patchy yellow regions, vividly underscores the critical importance of advanced in situ analytical techniques in gemological identification. Such methods allow for the accurate determination of color zone origins through the detailed analysis of spectroscopic features, advancing our understanding of these natural wonders.