May 22, 2022 10 min read

Why Do Diamonds Glow Under UV Light? Explained by Experts

Unlocking the Mystery: Discover Why Diamonds Glow Under UV Light. Dive into the mesmerizing world of gemstone brilliance!

Why Do Diamonds Glow Under UV Light

If you've ever seen a diamond under ultraviolet (UV) light, you may have noticed that it glows. This phenomenon is known as diamond fluorescence, and it's a fascinating characteristic that has puzzled scientists and gem enthusiasts for centuries. 

But why do diamonds glow under UV light? The answer lies in the unique atomic structure of diamonds, which causes them to emit light when exposed to certain wavelengths of UV radiation.

Diamond fluorescence occurs because the UV light excites electrons within the diamond, causing them to move to higher energy levels. When the electrons retreat to their base energy level, they emit energy in the form of visible light. The amount of fluorescence that a diamond exhibits can change based on factors like the intensity of the UV light, the color of the diamond, and the presence of impurities or defects within the diamond.

Key Takeaways

  • Diamond fluorescence causes diamonds to discharge visible light when exposed to UV radiation.
  • The intensity of diamond fluorescence can change depending on various factors, including the intensity of the UV light and the presence of impurities or defects within the diamond.
  • The presence of fluorescence in a diamond can impact its value and is considered when grading and certifying diamonds.

What is Diamond Fluorescence?

Diamond fluorescence is a phenomenon where diamonds discharge visible light when placed under ultraviolet (UV) light. This effect is caused by the absorption of UV light energy by the diamond's electrons, which then release the energy in the form of visible light.

Fluorescence can be observed in diamonds under different lighting conditions, including daylight, fluorescent lamps, and UV lamps. The fluorescence intensity can vary, with some diamonds exhibiting strong fluorescence and others showing no fluorescence at all.

The fluorescence color can also vary, with most diamonds exhibiting blue under long-wave UV rays. However, some diamonds can also fluoresce in other colors, such as yellow, green, or even red.

Diamond fluorescence does not affect the diamond's structural integrity or value. In fact, some people prefer diamonds with strong fluorescence as they can appear brighter and more vibrant under certain lighting conditions.

Color and Appearance of Diamonds Under UV Light

Diamonds may exhibit different colors and appearances when exposed to ultraviolet (UV) light. Some diamonds may glow blue, while others may appear milky or yellow. The color and fluorescence of a diamond under UV light can depend on various factors, such as the diamond's color grade and the presence of certain impurities.

Due to nitrogen impurities, diamonds with a yellow tint may appear more yellow or brownish under UV light. On the other hand, blue diamonds may exhibit a stronger blue fluorescence under UV light, amplifying their color and making them appear more sparkling.

The fluorescence of a diamond under UV light does not necessarily indicate its overall color grade. A diamond with a lower color grade may exhibit stronger fluorescence under UV light, giving it a whiter appearance. However, this does not necessarily mean that the diamond is of a higher quality or color grade.

In some cases, diamonds may appear milky or hazy under UV light, which can be caused by the presence of certain degrading elements or structural imperfections. This milky appearance can affect the diamond's fire and brilliance, making it appear less attractive.

The color and appearance of diamonds under UV light can vary depending on its color grade, level of impurities, and structural imperfections present. While fluorescence can enhance a diamond's color and make it appear whiter or more vibrant, it's important to consider other factors when evaluating its quality and value.

Intensity of Diamond Fluorescence

When exposed to UV light, diamonds can exhibit a range of fluorescence intensities. The intensity of diamond fluorescence can be classified into six categories:strong, very strong, medium, faint, none, and nil. The intensity of fluorescence is determined by the amount of energy absorbed by the diamond and the number of impurities present in the crystal lattice.

Diamonds with strong fluorescence emit a bright blue glow under UV light, while those with very strong fluorescence emit an even brighter blue glow. Medium fluorescence diamonds emit a slightly weaker blue glow, and faint fluorescence diamonds emit a very weak blue glow. Diamonds with no fluorescence do not emit visible light under UV light, while those with nil fluorescence do not react to UV light.

The strength of diamond fluorescence can affect its value, with some people preferring diamonds with strong fluorescence and others preferring those with none. It is important to note that fluorescence does not necessarily indicate a lower-quality diamond but rather a unique characteristic that can enhance or detract from its overall appearance.

Impact of Fluorescence on Diamond Value

Fluorescence is a common characteristic of diamonds, emitting a visible light when opened to ultraviolet (UV) light. The fluorescence of a diamond can have a significant impact on its value.

Diamonds with strong fluorescence may appear milky or hazy under certain lighting conditions, negatively affecting their appearance and value. On the other hand, diamonds with faint or no fluorescence may appear more transparent and brighter, leading to higher value and price.

The impact of fluorescence on diamond value also depends on other factors such as carat weight, quality, and color. For example, a diamond with a higher carat weight and better quality may have a higher value despite having strong fluorescence.

Fluorescence impact on diamond value is not always straightforward. In some cases, diamonds with strong fluorescence may be discounted, leading to a lower price. However, in other cases, diamonds with strong fluorescence may be of high demand by collectors and enthusiasts, leading to a higher price.

The overall impact of fluorescence on diamond value is complex and dependent on various factors. When evaluating a diamond's value, you have to consider its fluorescence in conjunction with other characteristics such as carat weight, quality, and color.

The Role of Impurities and Defects

When it comes to understanding why diamonds glow under UV light, impurities and defects play a crucial role. Nitrogen is one of the most common impurities found in diamonds, and it can cause the diamond toglow yellow under UV light. In contrast, boron impurities can cause the diamond toglow blue. These impurities affect how light is absorbed and emitted by the diamond, resulting in the characteristic glow.

Defects in the diamond crystal lattice can also cause the diamond to glow under UV light. For example, a single nitrogen atom can replace a carbon atom in the diamond lattice, forging a defect known as a nitrogen-vacancy center. This defect can cause the diamond to glow red under UV light. Similarly, a boron atom can replace a carbon atom, creating a defect known as a boron vacancy center, which can cause the diamond to glow green.

In addition to impurities and defects, how the diamond is cut and polished can also affect how it glows under UV light. The angle of the facets and the polish's quality can influence how light is reflected and refracted within the diamond, resulting in a more intense or subdued glow.

Diamond cutting is a highly specialized and precise process used to shape, facet, and enhance the appearance of diamonds, which are among the hardest known natural materials. The primary goal of diamond cutting is to maximize the diamond's brilliance, fire, and overall aesthetic appeal. 

Overall, impurities and defects in the diamond crystal lattice play a significant role in determining why diamonds glow under UV light. By aggregating these factors, researchers can better understand how to manipulate the properties of diamonds for use in various applications, from electronics to medical imaging.

Grading and Certification of Diamonds

When it comes to diamonds, grading and certification are operational standards. The Gemological Institute of America (GIA) is the most trusted and well-known organization for diamond grading. They evaluate diamonds based on the 4Cs: cut, color, clarity, and carat weight.

The GIA and other reputable gemological laboratories issue diamond grading reports. These reports provide a detailed analysis of the diamond's characteristics and quality. A GIA diamond grading report is the most generally recognized and respected certificate in the diamond industry.

Color grades are assigned to diamonds based on their lack of color. The spectrum stretches from D (colorless) to Z (light yellow or brown). Clarity grades are assigned based on the presence of internal and external characteristics. The scale runs from Flawless (no inclusions or deformities visible under 10x magnification) to Included (inclusions visible to the naked eye).

The cut of a diamond alludes to itsproportions,symmetry, andpolish. A well-cut diamond will bounce light back to the viewer's eye, creating a beautiful sparkle. Gemologists and trained professionals evaluate the cut of a diamond to ensure maximum brilliance and fire.

When purchasing a loose diamond, ensure it comes with a certificate. A certificate guarantees the quality and authenticity of the diamond. Retailers and jewelers should only sell certified diamonds to ensure customer satisfaction and trust.

Distinguishing Between Real and Fake Diamonds

Identifying real diamonds from fake ones is crucial in the jewelry industry. While there are many ways to distinguish between the two, the most reliable method is to identify characteristics unique to real diamonds. One such characteristic is the presence of inclusions or blemishes, which are natural imperfections that occur during the diamond's formation.

Another way to distinguish between real and fake diamonds is by their weight. Real diamonds are denser than fake ones, so they will weigh more for the same size. Additionally, real diamonds will have a high level of transparency and will not appear hazy or cloudy.

Lab-grown diamonds are another type of diamond that can be mistaken for fake diamonds. However, they are real diamonds that are created in a laboratory setting. These diamonds have the same chemical and physical properties as natural diamonds, which are just as valuable.

When it comes to identifying fake diamonds, there are a few things to look out for. Fake diamonds are often made of materials such as cubic zirconia or moissanite, which have a different chemical composition than real diamonds. They may also have a lower level of transparency and appear hazy or cloudy.

Identifying real and fake diamonds can be arduous, but it is imperative to ascertain its transparency and maintain the high quality of the diamond industry. By identifying characteristics such as inclusions, weight, and transparency, you can confidently distinguish between real and fake diamonds.

Special Cases and Exceptions

In some cases, diamonds may not glow under UV light due to compromised structural integrity. Diamonds that are hazy, cloudy, or oily may not exhibit fluorescence. Additionally, table-up diamonds may not show fluorescence due to light being reflected away from the pavilion.

Not all diamonds emit the same spectrum of fluorescence under UV light. Some diamonds may emit a different color or fluorescence intensity than others.

While artificial light can also cause diamonds to emit fluorescence, it is less strong than UV light. Durability should not be a concern when exposing diamonds to UV light, as it does not affect the crystal structure of the diamond.

It is also worth noting that while diamonds may emit X-rays and lasers, this is not related to their fluorescence under UV light. Some diamonds may exhibit phosphorescence, which is the emission of light after removing the UV light source.

When acquiring a diamond engagement ring, it must be evaluated by a gemological laboratory such as the Gemological Institute of America to ensure its authenticity and quality. Additionally, viewing the diamond upside down is recommended to observe its brilliance and ensure it is not hazy or cloudy.

While diamonds may not always exhibit fluorescence under UV light, they are still useful for identifying and evaluating gemstones.


The captivating world of diamonds continues to astonish us with its hidden secrets and mesmerizing qualities. As we've explored in this article, the phenomenon of diamonds glowing under UV light is a testament to their natural wonder and the brilliance of human craftsmanship. From the crystal lattice structure that traps and releases photons to the remarkable artistry of diamond cutting, every facet of this enigmatic gemstone is a testament to the delicate dance between science and beauty.

In the journey of understanding why diamonds glow, we've delved into the crystal lattice, impurities, and defects that make each diamond special. The experts have unveiled the intricate dance of electrons, revealing the hidden story within these stones. But beyond the science, the glowing diamond is a symbol of authenticity.

In an era of advanced technology and synthetic diamonds, the ability to glow under UV light is a powerful indicator of a diamond's natural origin. It's a testament to the diamond's geological journey, millions of years in the making, and the unique conditions that forged its brilliance. When you witness a diamond's ethereal glow, you're witnessing a connection to the Earth's history, a testament to its authenticity and rarity.

Frequently Asked Questions

Do all diamonds fluoresce under UV light?

No, not all diamonds fluoresce under UV light. The fluorescence of a diamond depends on the presence of certain impurities or structural defects in the crystal lattice. Some diamonds have a strong fluorescence, while others have a weak or no fluorescence at all.

What causes diamonds to fluoresce under UV light?

Diamonds fluoresce under UV light due to the existence of trace elements or structural imperfections in the crystal lattice. 

When the diamond absorbs UV light, it causes the electrons in the impurities or defects to become excited and emit light of a different wavelength, which is visible as fluorescence.

What colors can diamonds glow under UV light?

Diamonds can glow in various colors under UV light, including blue, green, yellow, and red. The fluorescence color depends on the type and concentration of impurities or defects in the diamond.

Can lab-grown diamonds also fluoresce under UV light?

Yes, lab-grown diamonds can also fluoresce under UV light. Like natural diamonds, the fluorescence of lab-grown diamonds depends on the presence of impurities or defects in the crystal lattice.

Is diamond fluorescence a sign of quality?

Diamond fluorescence is not necessarily a sign of quality. In fact, some high-quality diamonds may have no fluorescence at all, while others may have a strong fluorescence. The fluorescence of a diamond is simply a natural characteristic of the stone and does not necessarily affect its beauty or value.

Can diamond fluorescence affect the value of a diamond?

The effect of fluorescence on the value of a diamond depends on the individual stone and its other characteristics. 

In some cases, a strong fluorescence may enhance a diamond's beauty and increase its value. In other cases, it may have no effect or even decrease the value of the stone. Ultimately, the value of a diamond is determined by a coalescence of factors, including its cut, color, clarity, and carat weight.