Diamonds, formed deep within the Earth, sometimes exhibit a property known as fluorescence. This natural phenomenon occurs when a diamond emits a visible glow when exposed to sources of ultraviolet (UV) light, such as black lights or strong sunlight. It results from their atomic structure and composition. The glow is not considered a defect.
The Atomic Origins of Diamond Fluorescence
The underlying reason for diamond fluorescence lies in the presence of trace elements or structural imperfections within the diamond’s crystal lattice. During the immense pressure and heat of their formation, microscopic amounts of foreign atoms can become incorporated into the otherwise pure carbon structure. These impurities act as “activators” for fluorescence.
When exposed to UV light, these specific impurities absorb the high-energy UV photons. This absorption causes electrons within the impurity atoms to jump to a higher energy level. As these excited electrons subsequently return to their original, lower energy state, they release the absorbed energy as photons of visible light. The color of the emitted visible light depends on the specific type of impurity or defect present in the diamond.
Nitrogen atoms are the most common impurity responsible for fluorescence in diamonds. However, other elements like boron can also contribute to this effect, although they are far less common. Additionally, certain structural defects in the carbon lattice itself can also create sites that fluoresce under UV excitation. The exact arrangement and concentration of these atomic impurities dictate the specific fluorescent color and its intensity.
Why Blue Fluorescence Dominates
Blue is the most frequently observed color of fluorescence in diamonds, accounting for the vast majority of fluorescent stones. This prevalence is directly linked to the specific configurations of nitrogen atoms within the diamond’s crystal structure. When nitrogen atoms are present as isolated single atoms or in specific clusters, they are particularly efficient at absorbing UV light and re-emitting it as blue light.
Its unique electronic structure allows for the absorption of UV energy and the subsequent emission of photons in the blue region of the visible spectrum. While blue fluorescence is dominant, other less common impurities or defect structures can lead to different fluorescent colors. For instance, certain nitrogen-vacancy combinations can sometimes result in green or yellow fluorescence, but these are considerably rarer than blue.
Assessing Fluorescence and Diamond Beauty
Diamond fluorescence is systematically graded by gemological laboratories, such as the Gemological Institute of America (GIA), under controlled UV light conditions. These grades typically range from None, Faint, Medium, Strong, to Very Strong, indicating the intensity of the observed glow. This grading provides a standardized way to describe a diamond’s fluorescent characteristic.
For most diamonds, particularly those with faint to medium fluorescence, this characteristic has no discernible impact on their appearance under normal lighting conditions. The subtle glow is only visible when the diamond is exposed to a strong UV light source. There is a common misconception that fluorescence always negatively affects a diamond’s beauty, leading to a milky or hazy appearance.
However, this milky or oily effect is rare and typically associated only with diamonds exhibiting strong or very strong fluorescence. Even in these rare cases, the effect is often only noticeable under specific, intense lighting scenarios. In fact, some individuals prefer diamonds with faint to medium blue fluorescence, especially in diamonds with a slight yellowish tint. The blue light emitted by the fluorescence can subtly counteract the yellow, making the diamond appear whiter or more colorless to the eye in certain lighting.