Diamonds are known for their brilliance and sparkle, but do they really glow in the dark? The answer is yes, but only under certain conditions. Diamonds contain different chemical elements that, depending on their concentration, can cause them to fluoresce in a variety of colors when exposed to ultraviolet light. The most common color is blue, but diamonds can also fluoresce in yellow, red and green. When some real diamonds are subjected to a dark room with ultraviolet light, they can give off a certain glow.
This phenomenon is called fluorescence and approximately 35% of natural diamonds show some degree of this effect. In nature, the presence of certain chemical impurities within the diamond composition triggers this brilliant effect in the presence of an ultraviolet light source. Diamonds that belong to a group called type IIB tend to appear blue when exposed to UV light. The residual glow of a diamond varies in color from blue to pink and fiery red, depending on the diamond.
Some sources say that blue diamonds could be real, while others say that if a diamond turns blue, it's not of high quality. If a gem doesn't shine in dark light, it could fall into the category of natural diamonds that don't fluoresce. This is because when photons from UV sources hit the diamond, impurities found in the diamond will cause it to emit the shine and it is not present in CZ, which is a common counterfeit that scammers use to imitate diamond. Interestingly, diamonds can also glow under black light in a variety of other colors ranging from yellow, white, red, green and orange. To learn more about these brilliant phosphorescent gems, chemical engineers at the Gemological Institute of America studied the Aurora Heart Collection, which contains 239 colored diamonds and a series of type IIB blue stones, in addition to the Smithsonian's Esperanza diamond and its blue heart diamond. When diamond contains specific chemical impurities, it is likely to shine when subjected to ultraviolet light.
When a diamond tilts and swings at different angles, some of the light reflects off the surface of the facets instead of bouncing inside the diamond. If a certain gemstone does not shine in areas with less light, it would be inaccurate to assume that it is fake, since it could fall into the category of naturally extracted diamonds that lack fluorescence. Keep in mind that cut quality determines the brilliance of a diamond and not its ability to shine in low light conditions.