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Diamond Fluorescence Explained

The gleam and glint of a diamond can be so otherworldly that ancient cultures explained their existence as tears of the gods, shards of the stars, or the product of lightning. And one of the most fascinating qualities of some diamonds isn’t even visible to the naked eye. Or is it?

Diamond fluorescence is the phenomenon in which a diamond emits a glow under UV light. The result of otherwise invisible impurities, this effect will not present in most diamonds, but in other cases, it can result in diamonds that shine a stunning bright blue or other iridescent hues. 

Looks aside, there is debate about how fluorescence affects a diamond’s desirability. If you’re intrigued to know more about why diamond fluorescence happens, how often it occurs and its effects on a diamond price, read on—and you just may discover the fascinating essence of fluorescence. 

The Science of Diamond Fluorescence

Within the ideal geological conditions—usually volcanic and in most cases, billions of years ago—that are necessary to create diamonds, a few imperfections are to be expected. 

On their way to becoming Earth’s hardest natural mineral, the carbon molecules that create diamonds pick up a few trace amounts of other elements, like nitrogen, which is present in 98% of natural diamonds, boron, and aluminum among others.

A few of these elements and their molecular configurations are agitated, or heated up, by longwave ultraviolet light. The visible, often colorful light that we see as fluorescence is the molecules’ efforts to relax, or cool down, by discharging photons.

The Many Shades of Diamond Fluorescence

Diamond fluorescence is not to be confused with colored diamonds, in which impurities in the stone produce blue, pink, green, black and other colorations visible to the naked eye. 

But while one color represents the vast majority of fluorescent diamonds, the variety of trace elements and their mixtures also results in a rainbow of possibilities. This allows fluorescence to show up in a number of colors, which makes the effect that much more intriguing to many jewelry professionals and admirers. 

  • Blue – Around 95% of fluorescent diamonds emit blue light, caused by clusters of three nitrogen atoms, called N3 centers.
  • Green – Groups of two or four nitrogen atoms near a vacancy (a site where a carbon atom is missing from the molecular lattice) will create green fluorescence.
  • Yellow – Yellow fluorescence is caused by aggregations of nitrogen atoms creating planar defects in the diamond called platelets. One nitrogen atom that has taken the place of a carbon atom will produce an orangish yellow.
  • Orange – When one nitrogen atom is held next to a vacancy, it results in orange fluorescence. 
  • Red – Due to their boron and nitrogen content, blue diamonds like the Hope diamond exhibit red fluorescence and phosphorescence, meaning that the glow continues after the UV light is removed, sometimes for several minutes. 

Measuring Diamond Fluorescence

Only 25 to 35% of diamonds exhibit any degree of fluorescence. As such, while it is certainly an identifying characteristic and is indicated on a stone’s grading report, it is not one of the 4C factors—diamond cut, color, clarity, and carat—that go into a diamond’s grade.

The Gemological Institute of America (GIA) grades fluorescence on a five-point scale: 

  • None
  • Faint
  • Medium
  • Strong
  • Very Strong 

As suspected, given that most diamonds do not exhibit fluorescence at all, the rarity of diamonds in each category increases with the intensity of the effect. 

Man-Made Fluorescence

A popular misconception is that fluorescence is a convenient way to discern natural, mined diamonds from the lab-grown variety. This theory falters when considering that, while at least half of natural diamonds do not fluoresce, many lab-grown diamonds do

The patterns of a lab-grown diamond fluorescence can even help determine the method used to create it. The most common fluorescent shapes from synthetic diamonds include: 

  • Stripes
  • Crosses
  • Angular shapes 

Some diamond substitutes, such as cubic zirconia, are capable of fluorescing, as well. Additionally, treatments meant to enhance a diamond’s color, like radiation and annealing, can increase the natural diamond fluorescence. 

This seems to illuminate the conclusion that, indeed, nothing is perfect—and plenty of beauty lies in the imperfect. 

Is Fluorescence Good or Bad?

Scientists continue to discover new medical and industrial applications for fluorescence in nanodiamond particles.

Though when it comes to ornamental diamonds, since it is generally imperceptible and does not affect the structural integrity of the stone, fluorescence cannot be said to be either good or bad, but rather a matter largely of personal taste. 

However, there is debate as to the extent to which fluorescence can manifest in ways that are perceptible to the human eye without the aid of special UV light. Many in the diamond industry contend that strong fluorescence makes its presence known unassisted.

The Effect of UV Rays 

The sun is also a source of ultraviolet radiation, and even the GIA acknowledges that the same UV rays that compel us to lather on the SPF for beach days are also capable of triggering a subtle glow in stones with a strong fluorescent effect.

In this case, a diamond bearing a low color grade but strong fluorescence can be favorable. 

  • Yellow plus blue – For diamonds with a yellow tint (those in the lower color-grade ranges of I to N), a medium to very strong blue fluorescence may benefit the appearance of the stone’s color in sunlight.
  • Yellow minus yellow – Inversely, a yellow stone that exhibits the much rarer yellow fluorescence could be graded below the diamond color it would display indoors, where most of us spend the bulk of our diamond-brandishing time.

The International Gem Society (IGS) maintains that since 2008, when diamond color began to be graded under light containing UV equivalent to a bright, sunny day, “the effect of fluorescence is built into the color grade.”

They suggest that many diamonds with blue fluorescence are graded above their actual color, which under most lighting conditions would appear more yellow.

The Debate on Fluorescence and Transparency 

Another common theory is that fluorescence is tied to negative qualities in a diamond’s transparency. It is often the case that stronger fluorescence and higher color grades in the D to H range positively correlate with stones appearing cloudy, milky, hazy, or oily.

Other experts contend that fluorescence has little impact, if any, on the transparency of a stone unless it has an extremely rare light-scattering defect, in which cases fluorescence could exacerbate a haziness already present.

The GIA points to a study demonstrating that the average diamond customer is unable to detect clarity effects in fluorescent diamonds and that even industry experts differed in their perceptions of fluorescence’s effect, or lack thereof, on particular stones. 

Does Fluorescence Affect Price?

While it may or may not be possible to notice the effects of fluorescence on a diamond’s appearance, it is certainly possible to notice the effects on a diamond’s price.

In general, more intense fluorescence tends to drive a diamond price down. How much depends on the stone’s color grade, and for some of the reasons we’ve discussed above, fluorescence can result in a couple of different price points. 

  • High Color / Strong Fluorescence – Whether it’s a real phenomenon or a phantom one, perceptions about the diamond fluorescence’s effect on transparency results in diamonds with high color grades and strong fluorescence being priced much lower than diamonds in those color grades with no fluorescence. A Grade D diamond with strong fluorescence can be priced similarly to Grade G or H diamonds with no fluorescence.
  • Low Color / Strong Fluorescence – Due to the possible effects of blue fluorescence on yellow-tinted diamonds, stones of low color grades and medium to strong fluorescence have been known to see prices slightly higher than stones in the same color grade with faint or no fluorescence.

The bottom line? It’s helpful to keep fluorescence in mind as a price factor, but it’s certainly not the only factor to consider in a diamond. It comes down to your personal preferences and the attributes of the stone that you want to highlight the most. 

Diamond Nexus: Fluorescence to Flawless

As with all precious things, people form bonds with their diamonds and gems. However visible the effects of diamond fluorescence may be, whether you want a diamond that fluoresces or not comes down to personal preference, perhaps with a hint of cost considerations.

The Nexus Diamond™ alternative is a completely colorless diamond and internally flawless, so while our lab-created diamond simulants may not wow the blacklight party, there’s no yellow coloration to mask with sunlight and you’ll never describe them with words like milky, cloudy or dusty. 

All of our diamond alternatives are 90% the cost of mined diamonds, free of ethical concerns, more eco-friendly, and made to last forever. With jewelry from Diamond Nexus, the precious stone you bond with is designed to align with your values at a better value—so you can enjoy fine jewelry and the finer things in life, too. 


Gemological Institute of America. Is Diamond Fluorescence Good or Bad?

Gemological Institute of America. Fact Checking Diamond Fluorescence: 11 Myths Dispelled.

Gemological Institute of America. HPHT and CVD Diamond Growth Processes.

American Gem Society. Fluorescence in Diamonds.

International Gem Society. How Does Diamond Fluorescence Affect Price and Color?

Gems & Gemology. A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds.

Gems & Gemology. Measurement and Characterization of the Effects of Blue Fluorescence on a Diamond’s Appearance.

Scientific American. Diamonds: Tears of the Gods.
Smithsonian. Bombarded with ultraviolet light, the blue Hope Diamond glows red.

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