Triboluminescence

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Triboluminescence in quartz

The term triboluminescence (from Greek τριβείν tribein 'rub' and Latin lumen 'light') was coined by Wiedemann and Schmidt in 1895 for the occurrence of “cold light emission” when solids are subjected to strong mechanical stress. Today the term is defined a little broader and, for example, the luminescence that occurs when adhesive tape is unwound quickly belongs to this category.

Description and history

If you rub two pieces of sugar against each other in a completely dark room, with your eyes well adapted to the dark, you can see a faint bluish light. This observation goes back to Francis Bacon and is the original form of triboluminescence: light that is created when crystals break.

However, this phenomenon was not intensively researched until the beginning of the 20th century. Around 1900, Chugayev examined 510 inorganic and organic crystals for possible triboluminescent properties and found that 127 of them showed triboluminescence. Four years later, Max Trautz found out in a monumental study that 283 of the 827 crystalline substances examined showed triboluminescence. Of the large number of substances capable of triboluminescence, however, only a few had the light emission so bright that a color could be recognized. In addition, it quickly became apparent that the light emission often does not depend on the substances themselves, but on the method of crystallization. Even crystals of a crystallization batch behaved differently. It was also found that the voltages that occur during crystallization within a crystal or during shock freezing are often sufficient to trigger triboluminescence.

Scientific background

Triboluminescence is not a uniform phenomenon, but can be triggered in different ways. There are seven different stimulation mechanisms:

  1. Deformation luminescence
  2. Tribo-induced gas discharge luminescence
  3. Tribo-induced electroluminescence
  4. Tribo-induced photoluminescence
  5. Tribo-induced resonance radiation
  6. Tribo-induced thermoluminescence
  7. Light emission at phase transitions

Without a detailed examination, it is practically impossible to draw conclusions about the respective excitation mechanism only from the external appearance. One mechanism of action that has been proven for many materials is the excitation of nitrogen molecules by electrical discharges. These practically always occur when charges are quickly separated and there is a flashover. This could be proven by spectroscopic investigations. In addition, with the help of a microscope, the spark paths on the crystal surface could be observed as thin, crooked lines. In some cases, however, the spectrum of triboluminescence corresponds to that of fluorescence , that is, mechanical energy causes a direct transition of electrons into the excited state. It is not necessary to destroy the crystal, only the action of mechanical energy is sufficient. In principle, a tribo-induced light generator can be produced in this way.

Triboluminescence today

Today, triboluminescence is hardly studied scientifically. Recent work shows that unrolling adhesive tapes not only triggers triboluminescence, but also emits X-rays. The same applies to opening self-adhesive envelopes. In technology, triboluminescent materials, especially doped zinc sulfides, are used to get an overview of the mechanical load and the material flows within turbines or impact mills . In materials science, triboluminescent substances are used as functional fillers. Statements can also be made here about load peaks, microcracks and any internal damage using the light generated by mechanical stress.

Experimental

Triboluminescence from L-nicotine salicylate

Triboluminescence can be proven experimentally with simple means: All you need is a dark room, crystalline materials and something to grind, crush or grind. H. Brandl has compiled and described a selection of easily accessible materials. In the simplest case, you can observe triboluminescence when you smash a lump of sugar in the dark, crush it with a pair of tongs or rub two pieces together. This weak triboluminescence can be significantly increased by adding a small amount of methyl salicylate . Some of the compounds known to date shine so brightly that the triboluminescent light can be seen in daylight. These are the organic compound anthracene-9-carboxylate (blue triboluminescence, only with one (-) - menthyl radical, since triboluminescence has not yet been observed with racemic compounds and probably does not exist) and triethylammonium tetrakis (dibenzoylmethanato) europate ( III) (red triboluminescence). In addition, the triboluminescence of other rare earth complexes (with β-diketone ligands), such as tris (dipivaloylmethanato) terbium (III) -p-dimethylaminopyridine (green triboluminescence), is also visible in daylight.

Other triboluminescent substances are z. B .:

Web links

Commons : Triboluminescence  - collection of images, videos and audio files

Individual evidence

  1. ^ E. Wiedemann, GC Schmidt: About luminescence. In: Annals of Physics and Chemistry. 54, 1895, pp. 604-625.
  2. ↑ Ritsch, ratsch, x-ray. In: Berliner Zeitung. October 23, 2008 (Science).
  3. ↑ L. Tschugajew: About triboluminescence. In: Chem. Ber. 34, 1901, pp. 1820-1825.
  4. ↑ M. Trautz: Studies on chemiluminescence. In: Journal of physical chemistry. 53, 1905, pp. 1-105.
  5. ↑ Max Trautz: Report on the tribuluminescence. (pdf; 489 kB) In: ZEITSCHRIFT FÜR ELECTRONIK, ATOMISTIK; IONOLOGY; RADIOACTIVI ACTIVITY ETC. 1910, accessed April 27, 2011 .
  6. ^ AJ Walton: Triboluminescence. In: Advances in Physics. 26, 1977, pp. 887-948.
  7. ^ PA Thiessen, K. Meyer: Triboluminescence in deformation processes of solid bodies. In: Natural Sciences. 57, 1970, pp. 423-427.
  8. ^ Carlos G. Camara et al .: Correlation between nanosecond X-ray flashes and stick-slip friction in peeling tape. In: Nature. 455, 2008, pp. 1089-1092, doi : 10.1038 / nature07378 .
  9. ↑ Ian Sage, Grant Bourhill: Triboluminescent materials for structural damage monitoring . In: Journal of Materials Chemistry . tape 11 , no. 2 , 2001, p. 231-245 , doi : 10.1039 / b007029g .
  10. ↑ H. Brandl: The phenomenon of triboluminescence . In: MNU . No. 45 , 1992, pp. 195-202 .