Fluorescence is the emission of visible light by a substance when exposed to ultraviolet (UV) light. For diamonds, this means the stone may temporarily exhibit a colored glow when held under a UV light source, such as a black light. This phenomenon is a natural characteristic resulting from the diamond’s atomic structure. Not all diamonds possess this property, so the answer to whether all diamonds glow is definitively no.
The Direct Answer: Not All Diamonds Fluoresce
The majority of natural diamonds do not exhibit fluorescence; they are considered “inert” when exposed to ultraviolet radiation. Statistical data shows that only approximately 25% to 35% of natural diamonds display some degree of fluorescence. This reaction can range from an extremely subtle glow to a very strong, distinct illumination.
The idea that all diamonds glow is a misconception. Most diamonds remain unaffected by UV light, showing no visible reaction whatsoever. Fluorescence is therefore an exception, not an expected quality, across the diamond population.
The Atomic Cause of Fluorescence
The glow is caused by minor structural imperfections or the presence of trace elements within the diamond’s pure carbon lattice. These elements, primarily nitrogen atoms, become incorporated into the crystal structure during the diamond’s formation. The specific configuration of these impurities determines if the diamond will fluoresce.
When a diamond with these defects is exposed to UV light, the energy from the UV rays is absorbed by the trace elements, exciting their electrons to a higher energy state. As these excited electrons drop back down to a stable, lower energy state, they release the excess energy as visible light photons. This emission is observed as fluorescence. Blue fluorescence, the most common color, is attributed to the presence of three nitrogen atoms clustered together (N3 centers) within the carbon structure.
Understanding Color and Intensity Variations
The visible glow is not always the same color, though blue is the most common, accounting for over 95% of fluorescent diamonds. Rarer colors can include yellow, green, white, or orange, depending on the specific combination of trace elements and defects present. The color of the glow results directly from the wavelengths of light emitted by the excited electrons returning to their ground state.
The intensity of the fluorescence is graded by institutions like the Gemological Institute of America (GIA) using a five-level scale: None, Faint, Medium, Strong, and Very Strong. This assessment provides a standardized way to describe the strength of the glow a diamond exhibits under long-wave UV light.
Impact on Diamond Grading and Appearance
Fluorescence is considered an identifying characteristic on a grading report, not a grading factor like the 4Cs (cut, color, clarity, and carat weight). The presence of fluorescence can subtly influence the diamond’s perceived appearance, which affects its market value.
For diamonds in lower color grades (I-M range) that possess a slight yellow tint, blue fluorescence can be beneficial. The blue color acts as a complementary color to the yellow, neutralizing the faint yellowish tone and making the diamond appear whiter.
Conversely, strong or very strong fluorescence can cause a diamond to appear hazy, milky, or oily, particularly in the highest color grades (D-H). This hazy effect is statistically rare, occurring in less than 0.2% of all fluorescent diamonds submitted for grading.