Triboluminescence

The term Triboluminescence (from Greek τριβείν tribein, rub ' and Latin. Lumen ' light ' ) was coined in 1895 by Wiedemann and Schmidt for the occurrence of a "cold light emission " under strong mechanical stress of solids. Today we group the term somewhat and is, for example, the luminescence that arises during rapid unwinding of tape to this category.

Description and History

Rubbing in a completely dark room, with well- adapted to the dark eyes, two pieces of sugar cubes together so you can see a faint bluish light. This observation goes back to Francis Bacon and is the original form of Triboluminescence: light, which arises upon breaking of crystals.

This phenomenon has been studied extensively but only at the beginning of the 20th century. In 1900, examined Chugaev 510 inorganic and organic crystals on eventual Tribolumineszenzvermögen and found that 127 of them showed a Triboluminescence. Four years later, Max Trautz found in a monumental study that examined 827 of crystalline substances had 283 connections Triboluminescence. Among the great number tribolumineszenzfähiger substances but the light emission was so bright that you could see a color only a few. Additionally, showed very quickly that the light emission is often not dependent on the substances themselves, but by the method of crystallization. Even crystals to a crystallization batch behaved differently. In addition, it was found that often the stresses that occur during crystallization within a crystal or in shock freezing, enough to cause Triboluminescence.

Scientific background

Triboluminescence is not a unitary phenomenon, but can be triggered in different ways. It distinguishes seven different excitation mechanisms:

Without in-depth investigation, it is practically not possible to conclude only from the outer appearance to the respective excitation mechanism. A proven with many materials mechanism of action is the excitation of nitrogen molecules by electrical discharges. These mostly occur whenever quickly charges are separated and there is a rollover flash. This has been demonstrated by spectroscopic studies. Also have been observed as a thin, curved lines with the aid of a microscope, the radio paths on the crystal surface. In some cases, corresponds to the spectrum of triboluminescence but the fluorescence, i.e., mechanical energy, in this case causes a direct transition of electrons in the excited state. It is not necessary to destroy the crystal, but the action of mechanical energy sufficient for this. In principle, as the production of a triboinduzierten light generator is possible.

Triboluminescence today

Triboluminescence is hardly processed today. Recent work shows that when rolling out tapes not only triggered Triboluminescence, but even X-ray radiation is emitted. The same is true for the opening of self-adhesive envelopes. In industry triboluminescent materials, especially doped zinc sulfide, used to get an overview of the mechanical loading and the material flows within turbines or impact mills. In materials science triboluminescent substances are used as functional fillers. You can also make statements to peak loads, microcracks and possible internal damage resulting in mechanical stress on the light.

Experimental

Due to the simple experimental access Triboluminescence provides the ideal way to create a form of self- luminescence and observe. What's needed is just a dark room, crystalline materials and something to grinding, crushing or grinding. H. Brandl has compiled and described a selection of readily available materials. In the simplest case, one can observe Triboluminescence when one smashes a sugar cube in the dark, crushed with pliers or two pieces rub together. This weak Triboluminescence can be amplified by the addition of a small quantity of oil of wintergreen. Some of the previously known compounds shine so bright that you can already see in daylight the Tribolumineszenzlicht. It is the organic compound, anthracene -9- carbonsäurementhylester (blue triboluminescence, with a (-)- menthyl, since triboluminescence has not been observed for the racemic compounds, and probably does not exist ) and europat to triethylammonium ( dibenzoylmethanato ) ( III) ( red triboluminescence ), moreover, is the triboluminescence some more rare earth complexes ( with β -diketones ligands ), such as the tris ( dipivaloylmethanato ) terbium (III )-p- dimethylaminopyridine (green triboluminescence ) visible even in daylight.

More tribolumineszierende substances are, for example:

• Zinc sulfide
• Willemite
• Uranyl nitrate
• L- Nicotinsalicylat (only one of three crystal structures observed )
• Tape including tape on envelopes