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How did yellow diamonds come from?
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How did yellow diamonds come from?

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Yellow diamond is a type of color diamond. 

yellow is the second most common color.  But the yellow diamonds reaching the color level are very rare. 

The color -grade white diamonds cannot be called yellow diamonds. The internationally authoritative hierarchical institution to the yellow diamond color is GIA in the American Jewelry Academy, and the color of yellow diamonds from shallow to deep into 6 levels.

The formation principle of diamond color

After the white light of visible light enters the diamond, the diamond absorbs certain bands or wavelengths in the spectrum and returns or transmits the rest to the observer's eyes. This process is called selective absorption. The color of all substances is determined by this, and diamonds are also determined by it.

Returning to the color of the observer's eyes, which is the color of the object, is a combination of many light waves that have not been absorbed. If only a small amount or no light waves are absorbed, all light waves in the spectrum return, and the object appears colorless or white; If all spectra are absorbed, the object appears black, and there are infinite possibilities between the two.

There are two factors that affect the way diamonds absorb light or form color:

One is the presence of impurities, that is, atoms other than carbon atoms.

The second is structural defects, such as the lack of carbon atoms in the lattice or lattice distortion.

The structural defects that form colors, also known as color centers, are actually the common result of structural defects and impurities. The reason is that structural defects and impurities form open spaces that are filled by other impurity elements. Nitrogen is the most common impurity in diamonds and the main factor causing yellowing.

Firstly, why is it a nitrogen atom? This is because nitrogen atoms and carbon atoms in diamond cubic structures are of similar size and are more easily distributed in this structure, while other elements such as Cr and Fe are too large to enter the lattice easily.

When nitrogen atoms replace certain carbon atoms in diamond crystals (100 out of every one million carbon atoms are replaced), the N3 center, also known as the N3 color center, is formed, where three nitrogen atoms surround one hole. There is significant absorption (called N3 absorption) at 415nm in the visible light blue to purple region. The N3 center can absorb the spectrum from blue to the ultraviolet end, resulting in yellow diamonds. The more N3 centers there are, the more yellow the diamond becomes. This is the reason why yellow diamonds have different shades of color.

Distortion without impurities on the lattice can also form color centers, such as occasional stress or sliding surfaces in the octahedral direction during crystal growth. When light passes through, it may cause partial absorption, leading to a decrease in diamond transparency and resulting in a smoky gray or brown color.

The brownish yellow color of yellow diamonds is mostly related to nitrogen, while a few brownish yellow diamonds have been found to be caused by lattice defects related to hydrogen.

Cultivate the formation of yellow in diamonds

The diamonds cultivated by the HTHP method are mostly yellow series, which is because the diamonds synthesized by this method cannot form the N3 color center of natural diamonds due to their fast growth rate. The color of yellow or orange yellow diamonds cultivated by HPHT is due to the introduction of isolated nitrogen during the growth process, while the excess electrons in Ib type diamonds absorb blue light and form a yellow tone. As the content of lone nitrogen increases, the yellow color of diamonds will become increasingly bright. Due to insufficient control over nitrogen elements, the probability of forming bright yellow is very low.

The vast majority of CVD cultivated diamonds are lla type, with a very low probability of forming bright yellow, while the appearance of yellow cultivated diamonds is mostly attributed to the accidental or intentional addition of nitrogen.

yellow diamonds

Several Misunderstandings about Yellow Diamonds

Misconception 1: Any  diamond with yellow color is a " yellow diamond" 

Except for a very small number of Type IIa diamonds, almost all white diamonds contain a slight nitrogen element. Generally, white diamonds after grade H can see a slight yellow tone, and the lower the grade, the more obvious the yellow tone. This type of diamond with a yellow tone is not yellow diamond, and the more yellow it is, the lower the price.

Misconception 2: Yellow diamond color will fade

Yellow diamonds do not fade with wearing, their color is due to the effect of optics! Diamonds appear yellow because nitrogen atoms replace certain carbon atoms in the diamond crystal during their formation, beginning to absorb blue purple light. Its color is naturally formed and will not change in any way due to wearing.

Misconception 3: Yellow diamonds are all natural

Yellow diamonds can be artificially synthesized and can also be artificially manufactured through irradiation and color modification

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