What is Diamond Fluorescence?
Diamond fluorescence is the ability of a diamond to glow under ultraviolet (UV) light, occurring when it absorbs invisible UV radiation and then re-emits it as visible light. While most commonly observed as a blue glow, fluorescence can also manifest in other less frequent colors, including yellow, green, orange, or even red. Approximately 25% to 35% of diamonds exhibit some degree of fluorescence; reputable grading laboratories, such as the Gemological Institute of America (GIA), assess and categorize its strength. The GIA uses a five-level scale, ranging from “None” (no fluorescence) to “Faint,” “Medium,” “Strong,” and “Very Strong” fluorescence.
The Science Behind the Glow
The ability of some diamonds to fluoresce stems from the presence of specific trace elements embedded within their crystal structure. These elements were incorporated during the diamond’s formation. Nitrogen atoms are the primary impurity responsible for causing blue fluorescence in diamonds. Other elements, or unique structural defects, can lead to different fluorescence colors. When exposed to UV light, electrons within these impurity atoms absorb energy, moving to a higher, unstable state; as they return to their original levels, they release this absorbed energy as visible light. The specific color of the emitted light depends on the type and arrangement of the trace elements. This re-emission of light stops almost immediately once the UV light source is removed.
Fluorescence and Diamond Quality
For the majority of diamonds, the presence of fluorescence has no discernible impact on their appearance under typical lighting conditions, such as sunlight or indoor illumination. The glow is only visible when the diamond is exposed to a strong UV light source, like a black light. In some rare cases, particularly with colorless diamonds that exhibit “Very Strong” blue fluorescence, the diamond might appear milky, hazy, or oily in normal lighting. This effect is not common, occurring in less than 0.2% of fluorescent diamonds graded by the GIA. The diamond industry, including grading laboratories, meticulously assesses and notes the presence and intensity of fluorescence on diamond grading reports. Fluorescence can sometimes even have a beneficial effect on a diamond’s appearance; for diamonds with a yellowish tint, blue fluorescence can make them appear whiter. This occurs because the blue light emitted by the fluorescence visually masks the subtle yellow body color. While strong fluorescence can occasionally lead to a slight reduction in a diamond’s market value, especially for those exhibiting a milky appearance, its impact is generally negligible for the vast majority of diamonds.