What is fluorescence in a diamond
Over the years we've been asked this question time after time by our customers, to find out that many have heard different explanation to fluorescence by different jewelers. The fact is some diamonds show fluorescence and some don't, Fluorescence is the emission of visible light by a diamond when it is stimulated by invisible ultraviolet (UV) rays. It is a common characteristic of diamonds. The diamond simply glows under the UV lights, usually a blue color, which most often stops when the energy source causing it is removed. For more than 50 years, GIA has indicated the presence of diamond fluorescence on its diamond grading reports, but described it on the report as an identification characteristic only - not a grade, The five terms GIA uses to classify the intensity of the fluorescence are: None, Faint, Medium, Strong, and Very Strong. 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.
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. The bottom line is that faint to slight and even medium blue has no impact on the diamond's appearance or value. More than this (e.g. strong on grading certificates) can have negative or positive impacts depending on what color you are purchasing, but strong fluorescence is only to be avoided when it makes the diamond appear 'milkish', like there is a fog/haze inside.
What is it?
Florescence results from the interaction between a light's energy and the atoms in a diamond and makes diamonds glow in Ultraviolet light (which is found in sunlight). The most common color for fluorescence is blue. It is not so much whether there is fluorescence but the degree of fluorescence that matters. MEDIUM and STRONG fluorescence can make 'off white' diamonds appear whiter and can make white diamonds look bluer. As the best diamond color, D is actually a "Blue white" some decades ago, fluorescent diamonds used to be prized but since then the trend has reversed. When a diamond has fluorescence it can be categorized into just 5 levels from none, faint, medium, strong, and very strong per GIA grading system.
How does it happen?
Diamond is crystallized carbon. If there were traces of other minerals present e.g. nitrogen, boron (these are common element) present in the earth when the crystallization process occurred, the diamond will fluoresce. Blue is the most common color for the fluorescence.
Do all diamonds have fluorescence?
About 50-66% of the diamond has some fluorescence that can be observed under special conditions such as short wave ultra violet light. FAINT, SLIGHT or MEDIUM fluorescence has no visible impact on the diamond. 10% of the diamonds on the market have florescence that is strong it is some of these diamonds (according to GIA), only 3% that are to be avoided as they make the diamond look milky/hazy.
Here is a summary from GIA study on this subject:
"Some gem diamonds fluoresce, most commonly blue, to the concentrated long-wave ultraviolet radiation of a UV lamp. There is a perception in the trade that this fluorescence has a negative effect on the overall appearance of such a diamond. Visual observation experiments were conducted to study this relationship. Four sets of very similar round brilliant diamonds, covering the color range from colorless to faint yellow, were selected for the different commonly encountered strengths of blue fluorescence they represented. These diamonds were then observed by trained graders, trade professionals, and average observers in various stone positions and lighting environments. For the average observer, meant to represent the jewelry buying public, no systematic effects of fluorescence were detected. Even the experienced observers did not consistently agree on the effects of fluorescence from one stone to the next. In general, the results revealed that strongly blue fluorescent diamonds were perceived to have a better color appearance when viewed table-up, with no discernible trend table-down. Most observers saw no relationship between fluorescence and transparency." For more information see gia.edu/pdfs/W97_fluoresce.pdf which is the results of GIA research on this subject.