Fluorescent Gemstones

Beside their great colors, shapes and variety, gemstones exhibit other properties that make them even more attractive to collectors and the fashion world. One of those characteristics that not many people knows is the fluorescent properties that most of them posses. Fluorescence is a property that some materials exhibit when they are exposed to certain types of light. When some gemstones are irradiated with light they may fluoresce.

What exactly is fluorescence?

Fluorescence is a type of luminescence. Luminescence is basically any light not produced at high temperatures but at room temperature. Fluorescence refers to luminescent light produced by the action of gamma radiation, X-rays or more commonly ultraviolet (UV) light on an object. When an object is irradiated with UV light, which possess higher energy than visible light, it absorbs the energy of the beam and is "excited" to a higher energy level. In order to recover to its original state, the object will irradiate that energy in the form of heat and light. The light that is irradiated have a lower energy than the light originally used and usually corresponds to light that belongs to the visible spectrum.

Remember that UV light is invisible to the human eye, while visible light is the one people is able to detect with their eyes and correspond to all the different colors, starting from violet (high energy visible light) and finishing in red (low energy visible light). Depending on the energy used and the properties of the material (in this case the gemstone) different colors are obtained after irradiation. When the source of UV light is removed, the emission of light finishes.

Another interesting property of many substances is phosphorescence, another type of luminescence in which the material keeps emitting light after the source of excitation is removed. Gemstones can also exhibit phosphorescence. An example of this type of luminescence corresponds to the hope diamond, which is blue and phosphoresces red (emits red light) during several seconds after exposure to UV light.

Minerals and gemstones that fluoresce contains substances in their structure known as activators, which are the responsible for the absorption of high energy light when exposure and the subsequent emission of visible light. The most important activators are magnesium, lead and some rare-earth elements, especially europium. Different types of light can cause different responses from the same gemstone. When longwave UV is used, a gemstone can emit one color whereas when shortwave UV light is used, the same gemstone can emit light of a different color. Some gemstones can emit the same color after exposure to either short or longwave UV light. Others may fluoresce in one wavelength (long or short) but not in the other one.

The color and intensity of the fluorescence may vary among different species of the same minerals; this is because the substances that cause the fluorescence may vary according to the origin and formation of the gemstone.

Which gemstones exhibit fluorescent properties?

Rubies spinel, emeralds and hope diamond exhibit red fluorescence when exposed to shortwave UV light. Diamonds emit light after exposure to X-rays. Rubies can exhibit a variety of colors (orange, yellow, blue, violet and green) after exposure to either shortwave UV, longwave UV or X-rays. Colorless sapphire emits orange either at short or longwave UV light while Sri Lanka sapphire emits red at both wavelengths. Emeralds tend to emit red at any wavelength while topaz emits orange after exposure to shortwave UV light and X-rays.

Many other gemstones and minerals can be fluorescent or phosphorescent, a great property that can help us to not only recognized certain gemstones but to collect them. Fluorescent minerals and gemstones can be easily collected in the dark using a powerful UV lamp. Collecting gemstones for collection can be a fascinating and delighting experience due to the immense array of shapes, sizes, species, colors and localities around the world.