Large Treated-Color CVD Laboratory-Grown Diamond Rings
Laboratory-grown diamonds have become a prominent sector of the jewelry market. Part of the consumer appeal relates to the availability of stones with vibrant colors and the range of carat sizes. The New York laboratory received one submission of five laboratory-grown diamonds produced by chemical vapor deposition (CVD) set in variously designed metal rings (figure 1). These samples represent the wide range of stone colors and sizes created using CVD growth technology. CVD diamonds commonly undergo post-growth treatments to improve clarity and color. Post-growth treatments such as high-pressure, high-temperature (HPHT) processing, irradiation, and annealing are often necessary for a more desirable color result. High-temperature treatment may remove internal synthetic graining patterns to improve clarity. Gemologists identify the treatments based on subtle indicators using several methods, specifically spectroscopic data analysis.
Infrared absorption spectroscopy showed no absorption related to nitrogen or boron, classifying these CVD diamonds as type IIa. The visible/near-infrared absorption spectrum, taken at room temperature, displayed GR1 absorption in all five samples (e.g., figure 2). Photoluminescence spectroscopy revealed a GR1 emission and silicon-vacancy doublet at 736.6 and 736.9 nm in samples B–E. The SiV– doublet is usually indicative of CVD growth since it is rarely seen in natural diamonds or HPHT-grown diamonds. The presence of the SiV– reveals CVD growth but does not contribute to the color within these stones. The GR1 defect in these CVD diamonds is evidence of post-growth treatment that included irradiation causing alterations in bodycolor.
The data suggest the samples underwent various treatments including HPHT annealing, irradiation, and possible post-irradiation annealing. Based on spectroscopic data, sample A shows evidence of HPHT treatment due to the lack of the 468 nm peak, irradiation, and low-temperature annealing to create the orange color. The greenish blue colors for samples B and C were created with irradiation and possibly annealing. Both samples contained strong absorption from the GR1 center and a weak 666.5 nm peak that can be annealed out at temperatures ranging from 420° to 540°C (see A.T. Collins, “Spectroscopy of defects and transition metals in diamond,” Diamond and Related Materials, Vol. 9, Nos. 3–6, 2000, pp. 417–423). Sample D likely underwent irradiation and subsequent low-temperature treatment to create the yellowish orange color. The grayish green color in sample E was likely the result of HPHT treatment and irradiation with subsequent annealing. We consider the annealing temperatures to be low to moderate because of the lighter color result in sample E.
Gemological and spectroscopic analysis revealed that all five samples were type IIa CVD-grown diamonds that underwent post-growth treatment to achieve fancy colors. The laboratory-grown diamond market continues to develop, driven by consumer demand for these affordable mined diamond alternatives.
