CVD diamonds are a fascinating product of modern technology, but they sometimes exhibit a brownish hue before they undergo any treatment. This is due to a combination of factors related to the growth process and material properties. Let's break it down further:

1. Presence of Nitrogen:

• During the CVD diamond growth process, carbon atoms are deposited onto a substrate by breaking down a gas mixture (usually methane, CH₄). However, the process can inadvertently introduce other elements, like nitrogen, into the diamond structure.
• Nitrogen impurities are one of the main causes of the brownish or yellowish hues in diamonds. While nitrogen is commonly found in natural diamonds and sometimes in CVD diamonds, it can cause a colored light absorptionthat results in the diamond taking on a brownish tone.
• While nitrogen is often present in low concentrations, higher levels can lead to more noticeable color changes. In fact, some CVD diamonds are intentionally doped with nitrogen during the growth process to create colored diamonds, but when this isn’t controlled precisely, the result can be a brownish hue.

2. Hydrogen Incorporation:

• Hydrogen is another element that can be incorporated into the diamond during the CVD process. When hydrogen atoms are present in the diamond lattice, they can cause distortions that interfere with the crystal structure, leading to color defects like the brownish hue.
• This happens more commonly in diamonds grown under less controlled conditions or when the equipment used is not optimized. As a result, hydrogen-related defects can lead to colorations that need to be removed through post-growth treatment.

3. Defects in the Crystal Lattice:

• CVD diamonds may also have dislocations or point defects in their crystal lattice due to the way the atoms are deposited. These imperfections can affect how light passes through the diamond, causing a brownish tint.
• These defects can be caused by factors like temperature fluctuations during the growth process or slight imbalances in the gases used.

4. Post-Growth Treatment:

• Fortunately, the brownish hue can often be eliminated or reduced through post-growth treatment methods, such as:
  • High-temperature annealing: This process uses heat to remove color defects, allowing the diamond to become more colorless and clear.
  • Laser treatment: Diamonds can be treated with lasers to correct their color or remove any impurities that may cause discoloration.
  • Pressure treatment: Similar to the annealing process, this method involves exposing the diamond to high-pressure environments to alter the internal structure and improve the color.

5. Brownish Hue in Fancy-Colored CVD Diamonds:

• Interestingly, brownish CVD diamonds, particularly those with a light or medium brown color, can sometimes be further treated to produce fancy-colored diamonds, such as pink, blue, or even green. The presence of a brownish hue can sometimes serve as a base for transforming a diamond into another valuable color, leveraging advanced techniques.

6. Conclusion:

• The brownish hue in CVD diamonds is often a result of nitrogen or hydrogen impurities, or imperfections in the crystal lattice. The good news is that post-growth treatments can often correct this color issue, turning a brownish diamond into a colorless or vibrant colored diamond.