Properties of optically active vacancy clusters in type IIa diamond

Area of Science:

• Materials Science
• Solid State Physics
• Defect Physics

Background:

• Natural diamonds exhibit color variations, with brown coloration often linked to specific defects.
• Understanding these defects is crucial for diamond characterization and treatment.
• Previous studies suggest vacancy-related defects influence diamond color.

Purpose of the Study:

• To investigate the nature of defects responsible for the brown color in natural diamonds.
• To correlate optical properties with vacancy defect structures.
• To examine the effect of high-pressure, high-temperature (HPHT) treatment on these defects and color.

Main Methods:

• Positron lifetime spectroscopy was employed to analyze vacancy defects.
• Monochromatic illumination was used in conjunction with positron measurements.
• Optical absorption spectra were recorded for comparison.
• Samples included brown natural diamond, HPHT-treated colorless diamond, and naturally colorless type IIa diamond.

Main Results:

• Brown diamonds contain optically active vacancy clusters (40-60 missing atoms).
• These clusters show photo-excitation induced charge changes (neutral to negative).
• Vacancy clusters correlate strongly with optical absorption spectra.
• HPHT treatment, especially at 2500°C, reduces and eventually removes these clusters.
• Treated samples become optically similar to colorless diamonds with comparable positron lifetimes.

Conclusions:

• The study identifies specific vacancy clusters as the origin of brown coloration in natural diamonds.
• The optical activity of these clusters is linked to their charge state.
• High-pressure, high-temperature treatment effectively removes these color-causing defects, leading to decolorization.