Which statement about fluorescence under longwave UV is true for CVD lab-grown diamonds?

• A. CVD lab-grown diamonds fluoresce under longwave UV in most cases.
• B. Fluorescence under longwave UV is never observed in CVD lab-grown diamonds.
• C. It is extremely rare for CVD lab-grown diamonds to fluoresce under longwave UV.
• D. Fluorescence under longwave UV has no diagnostic value.

Answer: (C)

Fluorescence under UV light comes from specific impurities and lattice defects, and the likelihood of those centers forming depends on how the diamond was grown. CVD lab-grown diamonds typically have an impurity profile that does not favor the longwave UV fluorescence centers, especially when nitrogen content is kept low. That’s why seeing fluorescence under longwave UV is not common in CVD diamonds, making it extremely rare in practice. You may encounter occasional weak fluorescence in some samples, but it’s far from the norm.

It’s also useful to remember that fluorescence can provide a clue in distinguishing diamond types when used with other tests, but it isn’t a definitive diagnostic on its own.