Lab-grown diamonds (LGDs) share identical chemical, physical, and optical properties with natural diamonds, as they are composed of pure carbon atoms crystallized in the same structure. Like their natural counterparts, LGDs often exhibit fluorescence, which is a visible glow they emit when exposed to ultraviolet (UV) light. This characteristic is a common occurrence in diamonds, and its presence or absence is simply a factor of trace elements incorporated during the crystal’s formation.
Understanding Diamond Fluorescence
Diamond fluorescence is a form of luminescence where a material absorbs high-energy light and re-emits it as lower-energy, visible light. A diamond absorbs invisible UV light, which excites electrons in the crystal lattice, causing them to jump to a higher energy state. When these excited electrons return to their stable state, they release the excess energy as photons of visible light, which we perceive as a glow. The physical cause of this light emission is the presence of atomic impurities or structural defects within the diamond’s pure carbon lattice.
Gemological laboratories measure the intensity of this glow on a standardized scale that includes None, Faint, Medium, Strong, and Very Strong. This assessment is performed under controlled long-wave UV lamps, and the result is noted on the diamond’s grading report. While fluorescence is a reaction that occurs only under UV light, it is considered an identifying characteristic because the impurities causing it are permanently locked within the diamond’s structure. Fluorescence is distinct from phosphorescence, which is a rare effect where the diamond continues to glow briefly even after the UV light source is removed.
Fluorescence Colors and Their Causes in Lab-Grown Diamonds
The color of fluorescence in lab-grown diamonds relates directly to the type of atomic impurity or defect present in the carbon crystal. Blue fluorescence is the most common color seen in diamonds, both natural and lab-grown, often linked to the presence of single nitrogen atoms or the N3 defect center. However, the controlled environment of the lab can introduce other elements, leading to a wider spectrum of colors.
For instance, the introduction of boron during the growth process, which is used to produce near-colorless diamonds, can result in a distinct blue fluorescence. Conversely, defects known as Nitrogen-Vacancy (N-V) centers, where a nitrogen atom sits adjacent to a missing carbon atom, often produce orange, red, or sometimes yellow fluorescence. Other trace contaminants, particularly nickel or iron from the equipment or growth medium, can introduce unique defect centers that result in green or yellow-green fluorescence. These varied color centers allow gemologists to use fluorescence analysis as a tool for identifying a diamond’s growth method and origin.
How Growth Processes Determine Fluorescence
The two primary methods for creating lab-grown diamonds, High-Pressure, High-Temperature (HPHT) and Chemical Vapor Deposition (CVD), each introduce unique impurities that define their fluorescence profile. HPHT diamonds are grown in a chamber using a molten metal solvent-catalyst, typically an alloy containing iron, nickel, or cobalt, to dissolve a carbon source and precipitate diamond crystals. Trace amounts of these metal catalysts are incorporated into the crystal lattice, leading to metal-related defects that often cause green, yellow-green, or orange fluorescence, sometimes resulting in a characteristic cuboctahedral growth pattern visible under UV light. Additionally, if boron is introduced to produce colorless HPHT diamonds, a blue fluorescence reaction is common.
CVD diamonds grow by depositing carbon atoms layer-by-layer from a carbon-rich gas, resulting in a different impurity mechanism. The CVD process often results in diamonds that contain various point defects, such as the Silicon-Vacancy (Si-V) center or the Nitrogen-Vacancy (N-V) center, because of the hydrogen-rich plasma environment. These defects are responsible for the typical red, orange-red, or sometimes weak blue fluorescence that can be observed in CVD stones. The layer-by-layer growth habit of CVD diamonds frequently manifests as a distinct, layered or striped fluorescence pattern, which is a key identifying feature. Manufacturers often subject CVD diamonds to a post-growth HPHT treatment to improve color, which can alter the initial defects and change the resulting fluorescence color and intensity.
Practical Impact on Appearance and Grading
For the average consumer, the intensity of fluorescence is the most practical consideration, as it is documented on every professional grading report. In most diamonds, fluorescence graded as Faint or Medium has no discernible effect on the stone’s appearance in typical lighting conditions. However, the effect of fluorescence can be advantageous for diamonds with a slight yellow tint, specifically those in the I-K color range.
In these stones, a Medium to Strong blue fluorescence can optically counteract the yellow color, causing the diamond to appear whiter or closer to a higher color grade in daylight, which contains UV light. The negative perception of fluorescence arises from the rare instances where Very Strong fluorescence, regardless of color, can cause a diamond to appear milky, hazy, or oily, even in normal light. Because of this rare potential for a negative visual impact, diamonds with Strong or Very Strong fluorescence are sometimes priced lower than non-fluorescent diamonds of otherwise identical quality.