Real diamonds can glow when exposed to ultraviolet (UV) light. This phenomenon, known as fluorescence, occurs in some natural diamonds. It is a temporary effect.
Understanding Diamond Fluorescence
Diamond fluorescence describes the emission of visible light by a diamond when it absorbs ultraviolet (UV) radiation. This occurs when UV photons excite electrons within the diamond’s atomic structure, causing them to jump to a higher energy level. As these electrons return to their original state, they release absorbed energy as visible light. This glow is temporary, ceasing immediately once the UV light source is removed.
What Causes Diamonds to Glow
The glow in diamonds stems from specific impurities within their crystal lattice; nitrogen atoms substituting for carbon atoms are the most common cause. These nitrogen impurities absorb UV light and re-emit it as visible light. Their arrangement and concentration determine whether a diamond will fluoresce and how strongly. Other trace elements, such as boron, can also contribute, though less common than nitrogen. The absence of these impurities explains why many diamonds do not fluoresce.
Colors and Intensity of the Glow
The most common color of fluorescence is blue, accounting for approximately 95% of fluorescing diamonds. Diamonds can also glow in other colors, including yellow, green, orange, or red, depending on the specific impurities and their configurations. For instance, structural defects or the presence of boron can lead to different emission colors. Gemological laboratories grade the intensity of fluorescence as Faint, Medium, Strong, or Very Strong. An estimated 25% to 35% of natural diamonds exhibit some degree of fluorescence.
Fluorescence as an Identification Tool
While fluorescence is a property of many natural diamonds, it is not a definitive test for authenticity. Many real diamonds do not fluoresce, so a lack of glow does not indicate a fake stone. Diamond simulants, such as cubic zirconia or moissanite, can also exhibit fluorescence, sometimes with different colors or intensities. Some lab-grown diamonds are engineered to fluoresce, mimicking natural stones. Relying solely on fluorescence to determine if a diamond is real can be misleading; professional gemological testing, which involves a comprehensive analysis of various optical and physical properties, remains the only reliable method for authenticating a diamond.
How Fluorescence Affects Diamond Appearance
For most diamonds, fluorescence has no discernible impact on their visual appeal under normal lighting, as the glow is only visible when exposed to a strong UV light source, such as a black light. In typical indoor or outdoor lighting, fluorescence is generally imperceptible. However, a small fraction of diamonds with very strong blue fluorescence may exhibit a slightly “oily,” “milky,” or “hazy” appearance. This effect is rare and typically only noticeable in direct sunlight or UV-rich environments. In some cases, blue fluorescence can enhance diamonds with a faint yellow tint by making them appear whiter, as the blue light counteracts the yellow.