About Fluorescence

What makes some diamonds glow?

An intriguing phenomenon of some diamonds is that they appear to glow blue, and less often green, yellow, orange, or a combination of these colors when exposed to invisible ultraviolet rays. This glow is called fluorescence, and lasts only as long as the diamond is exposed to the ultraviolet rays.

The culprit nitrogen.

In most cases, fluorescence is caused by the presence of nitrogen as a trace element impurity in diamond. You may know that diamonds are composed of carbon atoms organized in a lattice-like crystal structure. Sometimes some carbon atoms are missing in the lattice. These single or multiple vacancies may each be filled by a nitrogen atom. For example, a single nitrogen atom trapped near a vacancy causes bright orange-yellow fluorescence. But most commonly, three nitrogen atoms in lattice positions adjacent to a vacancy cause blue fluorescence.

In addition to color, fluorescence also varies by strength – from none, faint, medium, strong, and very strong, as described on GIA grading reports. The fluorescence color and its intensity are additional characteristics that can help to identify a specific diamond.

A common feature of diamonds.

Fluorescence is a common phenomenon in diamond. Of all the diamonds submitted to GIA over the past decade, approximately 25% to 35% exhibit some degree of fluorescence. And of those, only 10% show strengths of fluorescence in the medium, strong, or very strong categories.

GIA studies have shown that the strength of fluorescence has no widely noticeable effect on a colorless or near-colorless diamond’s appearance. In fact, many prefer the appearance of diamonds that have medium to strong fluorescence. In very rare cases (fewer that 0.2% of the fluorescent diamonds submitted to GIA), some diamonds with extremely strong blue fluorescence may appear hazy or oily.

No impact on a diamond’s strength.

The presence of nitrogen or other impurity atoms in the diamond crystal structure does not have any influence on the hardness or durability of a diamond.

More information

Download the fluorescence FAQs.   Or for in-depth information, read the results of GIA's 1997 research study in the Gems & Gemology article, “A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds.”