Some gemstones change color in UV light due to the presence of impurities in their crystalline structure that are sensitive to ultraviolet rays. These impurities absorb UV light and emit a new color, causing the gemstone to change hue.
Gemstones are essentially crystals, meaning they are matter organized into regular and repetitive structures. Their beauty often comes from their precise composition and tiny chemical variations that determine their color and optical properties. Take the case of rubies and sapphires: both come from the same mineral called corundum, which is mainly composed of aluminum oxide. The only small difference is a few tiny traces of other elements! In rubies, traces of chromium give them their bright red color, while in sapphires, it is often iron or titanium that provides the deep blue or other nice shades. The emerald, on the other hand, belongs to the beryl family — a mineral rich in beryllium and aluminum — turned green thanks to some traces of chromium and sometimes vanadium. In short, the secret of gemstones often lies in very slight differences: tiny chemical variations that create all the magic!
Gemstones have a network-organized structure, a kind of crystalline atomic scaffolding. When they are exposed to ultraviolet rays, their structure absorbs part of this intense energy. Some electrons that quietly orbit around their atoms are then temporarily boosted to higher levels: this is an excited state. When they return to their original position, these electrons will release the accumulated energy in the form of visible light, thereby temporarily changing the perceived color. This light emission is directly dependent on the specific arrangement of atoms in the crystal structure, explaining why each type of stone shines differently under UV.
Some gemstones contain tiny amounts of impurities, often metals like chrome, iron, or manganese. These elements trap some of the energy when UV light hits the stone. They absorb and then re-emit this energy as visible light: this is called fluorescence. Sometimes, the energy remains trapped a bit longer and slowly comes out even after the UV light is turned off; this is phosphorescence. The exact nature of the impurities determines what color the stone will take under UV light. Each metal has its precise light signature, offering unique reflections.
It's a story of electrons. When a mineral receives UV light, its electrons absorb this energy and temporarily move to an excited state (basically, they jump up to a higher energy level). Not a very stable situation! They quickly want to return to their normal position, their ground state. When they go back to their initial state, they release this absorbed energy in the form of visible light. This phenomenon is called fluorescence. Some materials stay excited a little longer and slowly release this energy: this is phosphorescence, the nice "glow-in-the-dark" effect that persists even after the UV light is turned off. The color you see directly depends on the energy gaps between these electronic states and the nature of the elements present in the stone.
Willemite and calcite found in certain mines in New Jersey are famous for their incredible multicolored fluorescence under UV light, making these extraction sites popular natural light shows for collectors.
In gemology, observing the behavior under UV light is sometimes used to differentiate natural stones from synthetic diamonds, as the latter may exhibit specific fluorescent patterns.
Fluorescence, responsible for the color change of certain gemstones under UV light, derives its name from the mineral fluorite, known for its exceptional ability to glow under ultraviolet light.
The "Hope" diamond, famous for its mysterious blue color, emits a strong red phosphorescence when exposed to UV light, a phenomenon used to verify its authenticity.
No, the effect produced under UV light is temporary. As soon as the ultraviolet light stops, the gemstone almost instantly returns to its original color. This phenomenon is due to the rapid release of the energy absorbed by the atoms or molecules present in the crystalline structure.
The main difference lies in the duration of the phenomenon: fluorescence is only visible during exposure to UV light and stops immediately after the irradiation ceases, whereas phosphorescence persists for a few seconds to several minutes after the exposure to UV light has ended.
In general, short and moderate exposure is not dangerous. However, prolonged or repeated exposure to intense UV radiation could slightly alter the appearance of certain sensitive or delicate stones. Therefore, it is advisable to limit such occurrences.
No, not all gemstones necessarily react under UV light. Only certain stones containing specific elements, known as impurities or activators, will exhibit fluorescence or phosphorescence under UV.
Yes, fluorescence or phosphorescence can influence the value of a gemstone depending on its intensity and the visual effect it produces. In some rare cases, this increases its value by making it more aesthetically pleasing and attractive to collectors.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
