The Science of the Glow
When a diamond with fluorescent properties is exposed to ultraviolet (UV) light, it absorbs energy from UV photons. Absorption occurs at specific locations within the diamond’s crystal lattice, where atomic structures or impurities are present. This absorbed energy causes electrons within these particular atoms to become excited, elevating them to a higher energy state.
These excited electrons remain in this elevated, unstable energy state for only a fleeting moment. To regain stability, they release this excess energy as visible light photons, creating the diamond’s glow. This energy transformation from invisible UV light to visible light defines fluorescence.
The specific color of the visible light emitted, such as the common blue glow, is determined by the distinct energy levels involved in the electron transitions and the nature of the impurity or defect causing the fluorescence. As soon as the external UV light source is removed, the electrons return to their ground state, and the diamond’s glow immediately ceases.
Trace Elements and Diamond Fluorescence
Diamond fluorescence stems from specific trace elements or structural defects incorporated during its natural formation. These elements act as impurities within the diamond’s carbon lattice. The most common element responsible for diamond fluorescence is nitrogen.
Nitrogen atoms, in particular configurations within the diamond’s crystal structure, absorb UV light and re-emit it as visible light. For example, a common cause of blue fluorescence, observed in over 95% of fluorescent diamonds, is the N3 center, a specific arrangement of three nitrogen atoms around a vacancy in the carbon lattice. Nitrogen is found in approximately 75% of all diamonds that fluoresce.
While blue is the predominant color, other trace elements can cause different fluorescent hues. Boron, for instance, is often linked to yellow or green fluorescence, though it is a less common impurity, found in about 2% of diamonds. Other elements like hydrogen and aluminum, or structural irregularities, can also contribute to the diverse colors and intensities of fluorescence.
Fluorescence and Diamond Appearance
Diamond fluorescence is graded by gemological laboratories, such as the GIA, on a scale that includes “None,” “Faint,” “Medium,” “Strong,” and “Very Strong.” This grading indicates the glow’s intensity when the diamond is exposed to long-wave UV light. Approximately 25-35% of diamonds exhibit some level of fluorescence, but for the vast majority, this characteristic has no noticeable impact on their appearance under normal lighting conditions.
For most diamonds, including those with faint to medium fluorescence, the glow is only visible under concentrated UV light sources like a blacklight. The average person cannot distinguish between a diamond with faint or medium fluorescence and one without, especially outside a laboratory setting.
A common concern is that strong or very strong fluorescence can cause a diamond to appear “oily,” “milky,” or hazy. This effect is extremely rare, occurring in under 0.2% of fluorescent diamonds submitted to the GIA. When it does happen, it is typically limited to diamonds with very strong fluorescence in higher color grades (D-F), where it might reduce transparency.
Conversely, faint to medium blue fluorescence can sometimes enhance a diamond’s appearance. In diamonds with a slight yellowish tint (typically I to M color grades), the blue fluorescence can visually counteract the yellow, making the diamond appear whiter or more colorless. This can be a desirable effect, particularly in natural daylight, which contains some UV radiation.
From a market perspective, diamonds with strong fluorescence, especially in high color grades, may sometimes be priced lower due to historical perceptions. However, for most diamonds, particularly those with faint to medium fluorescence, this characteristic generally does not negatively influence value or visual appeal. Many buyers find diamonds with some fluorescence to offer good value, as its impact on beauty is often negligible or beneficial.