Vacancy clusters, dislocations and brown colouration in diamond

Area of Science:

• Materials Science
• Solid State Physics
• Geology

Background:

• Natural diamonds exhibit brown coloration attributed to vacancy clusters.
• Dislocations in diamonds are known to influence their optical and electronic properties.

Purpose of the Study:

• Investigate the role of dislocations in sub-bandgap absorption in natural diamonds.
• Understand the effect of high-pressure, high-temperature (HPHT) annealing on vacancy clusters and diamond coloration.

Main Methods:

• Optical absorption spectroscopy on natural brown and colorless diamonds.
• Analysis of diamond samples before and after HPHT treatment.

Main Results:

• Dislocations exhibit sub-bandgap absorption, similar to theoretical predictions for shuffle dislocation segments.
• HPHT annealing leads to the growth of vacancy clusters trapped in dislocation strain fields, reducing their numbers and optical absorption.
• Observed absorption at dislocations is present in both brown and colorless diamonds, suggesting a general phenomenon.

Conclusions:

• Dislocations contribute to sub-bandgap absorption in diamonds, but vacancy clusters are the primary cause of brown coloration.
• HPHT annealing effectively reduces diamond coloration by altering vacancy cluster configurations at dislocations.
• The presence of vacancies at dislocations is crucial for forming specific configurations that influence coloration.