Fluorescence, a captivating phenomenon where materials emit light upon exposure to ultraviolet (UV) radiation, has intrigued scientists, artists, and enthusiasts alike for centuries. This magical transformation occurs due to the interaction between photons and electrons within the material, resulting in a visible glow that ranges from subtle to vibrant.
Historical Insights
16th Century: In the mid-1500s, the Spanish Franciscan missionary Bernardino de SahagĂșn described the properties of certain Mexican plants that exhibited glowing characteristics under certain conditions. However, these observations were not systematically studied.
17th Century: In the late 1600s the English natural philosopher Robert Boyle, noted the strange glowing properties of certain natural substances like quinine, which fluoresced under specific conditions. His observations laid the groundwork for future explorations into the nature of light and luminescence.
Early 19th Century: In the early 1800s, Scottish scientist Sir David Brewster conducted experiments on various materials and noted the emission of light, calling it "internal dispersion." While not yet termed fluorescence, his work added to the growing body of knowledge.
In 1852, the British scientist Sir George Gabriel Stokes made a ground-breaking discovery while studying the mineral fluorite. He observed that fluorite emitted a blue light when exposed to ultraviolet light. Stokes coined the term "fluorescence" from the mineral fluorite and described the phenomenon as the emission of light at a longer wavelength after absorbing light of a shorter wavelength. His work was pivotal, leading to the formulation of Stokes' Law, which states that the wavelength of emitted light is always longer than the wavelength of the absorbed light.
Causes of Fluorescence
At its core, fluorescence is caused by the absorption of high-energy photons (typically UV light) by a material's electrons. These electrons briefly enter an excited state before returning to their ground state, emitting lower-energy photons in the process. This emission results in the characteristic glow associated with fluorescence.
Applications in Industry and Science
The unique properties of fluorescence find widespread use across diverse industries. In mineralogy, it aids in the identification and categorization of minerals, as different minerals exhibit distinct fluorescence patterns under UV light. In manufacturing, fluorescence is utilized in quality control processes, where it helps detect imperfections in materials such as textiles and plastics.Â
The discovery of fluorescent dyes, such as fluorescein, and their applications in biology and medicine revolutionized diagnostics and research. Fluorescent microscopy became a powerful tool for visualizing cells and tissues, aiding in countless scientific discoveries.
If you have watched Outback Opal Hunters you may have seen the miners âblack-lightingâ â a term used to describe the use of UV lights at night or in a darkroom to find opal, which fluoresces brightly and is much easier to see in the dark than in the daytime. It is such an effective method for spotting opal I am often surprised how few miners use the technique. You may also have seen the use of UV torches on crime scene investigation programmes, they are really effective for finding traces of fluids that would otherwise be invisible. Absolutely under no circumstances should you use a UV torch in a hotel room or your own bathroom - you will be horrified.
UV Lights and Wavelength Variations
If you want to see fluorescence you really need a UV torch. UV lights come in different wavelengths, such as longwave (UVA) and shortwave (UVB), each revealing unique fluorescence properties in materials. Shortwave UV lights should be used with extreme caution, the rays can burn skin and damage eyes. A much safer option is Longwave or Mediumwave. Longwave torches are available on Amazon, the USB chargeable ones are great. As a gemmologist and mineralogist I use my UV torch all the time. It is a very fast and simple tool that can help identify materials quickly based on their UV responses (or lack of). In most cases a UV torch alone isnât sufficient to confirm identity but it certainly helps.
Beauty of Fluorescence
Beyond its scientific applications, fluorescence adds a mesmerizing dimension to art and aesthetics. Gemstones like diamonds, opals, and fluorite often exhibit stunning fluorescent properties, enhancing their allure and value. The play of colours and light intensifies under UV illumination, transforming these stones into natural works of art. The sheer range of colours and patterns is incredible and many people collect gems or crystals for their fluorescent properties.Â
Mineral Examples
Take fluorite, for instanceâa mineral known for its fluorescence variability. While some specimens fluoresce vividly under UV light, others may exhibit no fluorescence at all due to variations in their chemical composition and impurity levels. Â Fluorite is a very popular crystal because of its fluorescence as well as its metaphysical properties. Sodalite sometimes has a strong orange fluorescence.Â
Calcite is another mineral that often exhibits strong fluorescence, often in pink and yellow hues.
Gemstone Examples
Opals, rubies, emeralds, pearls and sapphires often have strong fluorescence. Sometimes the presence of iron can mask fluoresce, for this reason you rarely find garnets that fluoresce - garnets have heavy concentrations of iron. The colour of the fluorescence can sometimes help in identifying where the gem has come from, for example some Sri Lankan sapphires have an apricot fluorescence which is characteristic, other sapphires will typically fluoresce red.Â
Natural Diamonds and Fluorescence
Interestingly, approximately 25% to 35% of natural diamonds exhibit fluorescence when exposed to UV light. This fluorescence can manifest in many colours, but blue is the most common. Jewellers often consider fluorescence when assessing a diamond's quality, as it can either enhance or diminish its appearance depending on the specific lighting conditions. Typically a diamond that has a strong fluorescent response will be 16% cheaper than one that does not. Strong fluorescence can sometimes cause a diamond to look hazy, oily, or milky under certain lighting conditions. This is particularly true for diamonds with very strong fluorescence. Such effects can detract from the diamond's clarity and brilliance, making them less desirable to buyers. In reality this price difference will only apply to stones over 0.50 carats, smaller stones such as those surrounding coloured stones as shown in the rings above are rarely price affected by UV responses. Personally I think the UV responses add something special and I really don't mind if my diamond glows blue in the dark.
Synthetic diamonds (lab created) often have very different UV responses to UV light which can help to distinguish them from natural (earth mined) stones.
Collecting UV Minerals
Enthusiasts and collectors are drawn to UV minerals for their otherworldly glow and the thrill of discovering hidden fluorescent treasures. From fluorescent calcite to willemite, each mineral exhibits a distinct fluorescence pattern that adds excitement to the pursuit of UV mineral collecting. At mineral shows it is not unusual to see people carrying a handful of torches around with them, one for each - SW, MW and LW. They shop by torch and I always ensure that I have a good selection of pieces that have wonderful UV responses.
Conclusion
Fluorescence transcends mere scientific curiosityâit is a phenomenon that bridges art, science, and industry. From its historical roots to modern applications, fluorescence continues to captivate and inspire, offering a glimpse into the luminous secrets hidden within the natural world. Whether adorning a gemstone or illuminating a mineral specimen, fluorescence invites us to appreciate the beauty and complexity of light in its most radiant form.
Check out the amazing fluorescent minerals over at the Geminlogical shop, the wavellite, calcite and fluorites are very ethereal.
