At first glance, this blue-purple glowing mineral seems almost unnatural. But it is not illuminated in blue by artificial light. It is a hackmanite that fluoresces under UV light.
Fluorescence is based on the effect of light: If high-energy radiation such as UV light hits an atom or molecule, it can happen that part of its energy is absorbed by the electrons in the material. As a result, they briefly jump onto a lane further out. After a short time, however, the electrons fall back on their original path and release the excess energy again. This is released as radiation – the fluorescent light. Typically, the light emitted is slightly lower in energy than the light emitted before. The UV light that is invisible to us is therefore emitted again as visible light.
It is precisely this phenomenon that an international team of researchers led by Mika Lastusaari from the University of Turku has investigated in more detail with the mineral hackmanite. This occurs naturally in Afghanistan, Greenland, Canada and Pakistan and appears under normal light in an inconspicuous gray color. Under UV light, however, it glows in blue-violet colors.
During their analysis, the scientists were particularly interested in which components are responsible for the fluorescence of this natural mineral. Many minerals get their fluorescence from ions that are integrated into the crystal lattice and whose electrons are particularly easy to excite. For example, naturally occurring apatite crystals owe their glow, among other things, to manganese ions and ions of rare earth metals.
With the help of experiments with UV light and calculations, the research team has now also identified the components that give the hackmanite its bright color in this photo. According to this, the composition of the mineral from sulfur, potassium, titanium and iron plays a decisive role.
Based on their results, the researchers were finally able to develop a synthetic material that fluoresces for significantly longer than the model on our picture. “Nature has helped significantly in the development of increasingly effective luminous materials,” explains Lastusaari. The new findings should also be used in the future for the development of better synthetic materials that are already used today, for example for self-luminous emergency exit signs.