- Fluorescence is an optical phenomenon that makes diamonds emit visible light (usually blue) when exposed to ultraviolet light
- Fluorescence can influence a diamond´s price as well as its appearance, that´s why it is stated in every gemological certificate
- Important: In gemology fluorescence is not a quality feature, but rather a characteristic for identification
- In 95% of fluorescenet diamonds the color is blue, however, in rare cases different colors are possible as well

The changes in a diamond´s crystal struture that can both - cause and prevent fluorescence - are in no way disadvantageous for the gem stone (more on this). About 25-35% of all diamonds have a varying degree of fluorescence. The intesity of the emitted visible light is graded accordingly:

Term on the certificate	Explanation
None	The diamond shows no fluorescence
Faint	UV light makes the diamond show a slight blueish shade
Medium	The diamond emits visible light when exposed to ultraviolet light
Strong	The reaction to UV light is clearly visible
Very Strong	The diamond glows in an intense blue color when exposed to UV light

None	Faint	Medium	Strong	Very strong

Expert advise:
Fluorescence plays an important role in diamonds when speaking about its appearance as well as the price. If you like this special optical phenomenon (only 25-35% of all diamonds have it) and find it fascinating, then you should enjoy the discount on these gem stones. We will help you make the right decision in your specific case and can have our partners examine every diamond beforehand.
If you intend to buy the diamond thinking of it as an investment at the same time, we recommend you follow the market view and pay the premium for non-fluorescent diamonds.

Additional information: The diamond certificate describes fluorescence as a reaction to long-wave ultraviolet light at 366 nm. Short-wave ultraviolet radiation at 254 nm is relevant in a different context. More on this here.

Influence on price

Fluoroscent diamonds are usually sold on a discount in the market. Among high color grades (D-G) the difference in price can be up to 15%. The market considers fluorescence disadvantageous which is expressed in price. One reason could be the fear of the so called "overblues": Diamonds with extremly strong fluorescence that can cause the stone to appear hazy. The most famous example for this is the 127 carat "Portugese Diamond", the largest cut diamond of the Smithsonian Collection.

From a gemological point of view studies of the Gemological Institute of America (GIA) come to a different conclusion regarding fluorescence in diamonds - especially when used in jewelry. According to GIA studies the overwhelming majority of fluorescent diamonds do not show any negative relation or influence on the appearance of the gem stone. On the contrary: In many cases test subjects would welcome the effect of fluorescence - for diamonds that show a little color, the blueish fluorescence actually neutralizes the yellow color shade and makes the gem stone appear brighter. This is proven by the most important results of the GIA study from 1997:


1)    The (positive) effect of fluorescence on the appearance of diamonds becomes most obvious at lower color grades I to K. At the same time the (negative) effect of fluorescence on price is most prominent among high color grades.
2)    The occurence of "overblues" that account for the negative influence of fluorescence on price is extremely rare. Not more than 0.2% of all fluorescent diamonds that are graded by GIA have the hazy appear. In fact, there are so few diamonds of this kind that GIA could not find enough stones to conduct a separate study on the topic.

Interesting in this discussion is also a historical aspect:

In the beginning of the 20th century the finest, colorless and most transparent diamonds were called "Blue Whites". The term relates to the blueish color tone that was caused by fluorescence. Back then the blue glow was considered additional sparkle and a quality feature. The enhancing effect of fluorescence on the color grade of the gem stone was well-known even then. However, in the standardization process of the American Trade Commission the term "Blue White" was declared misleading and was since reserved for actual blue diamonds. In addition, the enchancing optical effect interfered with the process of standardization of evaluation and grading systems for diamonds. In the beginning everybody used different lighting conditions without UV filters and therefore graded diamond color differently. Originally Blue Whites came from the South-African Jagersfontein mine. Not only the term "Jager" was used as a synonym for Blue White, but Jager also referred to the highest color grade of a diamond.

Changes in the crystal structure

Diamond is a pure mineral. Yet, structural defects in its crystal structure may occur. Single or multiple atoms of mainly nitrogen, hydrogen and boron can be found in between the carbon atomic structure. In most cases nitrogen is the impurity in the crystal structure - which is also responsible for the yellow color in most diamonds. Changes in the crystal structure can cause and prevent fluorescence. Important is the amount of nitrogen atoms:

i) A group of two nitrogen atoms, the A aggregation, prevents fluorescence
ii) A group of three nitrogen atoms, the N3 center, causes blue fluorescence
iii) A group of four nitrogen atoms, the B aggregation, is neutral
iv) One single nitrogen atom is responsible for yellow fluorescence
v) In addtion there is a range of other possibilities and combinations of the above nitrogen variations, that influence the occurence of fluorescence differently