Triboluminescence

Triboluminescence is an optical phenomenon in which light is generated via the breaking of asymmetrical bonds in a crystal when that material is scratched, crushed, or rubbed. This is a variant of luminescence; the term comes from the Greek tribein (to rub) and the Latin lumen (light).

For example, a diamond may begin to glow while being rubbed. This occasionally happens to diamonds while a facet is being ground or the diamond is being sawn during the cutting process. Diamonds may fluoresce blue or red. Ordinary friction tape (the cloth type — not the shiny electrician's tape) displays a glowing line where the end of the tape is being pulled away from the roll. Many postal envelopes will produce a blue glow when opened in the dark or in low-light conditions. Also, when sugar crystals are crushed, tiny electrical fields are created, separating positive and negative charges that then create sparks while trying to reunite. WintOGreen Life Savers work especially well for creating such sparks, due to the fact that wintergreen oil (methyl salicylate) is fluorescent and converts ultraviolet light into blue light. Some Band Aid wrappers also glow bluish-green when unwrapped swiftly.

The discovery of triboluminescence was accidental. In the late 1790's sugar production began to produce more refined pure sugar crystals. These crystals were formed into a large solid cone for transport and sale. This solid cone of sugar had to be broken into usable chunks using a device known as a sugar nip. People began to notice that as sugar was "nipped" in low light, tiny bursts of light were visible. The first recorded observation however, occurred even earlier and is attributed to English scholar Francis Bacon when he wrote in his 1620 "Novum Organum"[1] that "It is well known that all sugar, whether candied or plain, if it be hard, will sparkle when broken or scraped in the dark.". The scientist Robert Boyle also reported on some of his work on triboluminescence in 1663.

Additional recommended knowledge

Essential Laboratory Skills Guide

Safe Weighing Range Ensures Accurate Results

Weighing the right way

Mechanism of action

Materials scientists have not yet arrived at a full understanding of the effect, but the current theory of triboluminescence — based upon crystallographic, spectroscopic, and other experimental evidence — is that upon fracture of asymmetrical materials, charge is separated. When the charges recombine, the electric discharge ionizes the surrounding air, causing a flash of light. Research further suggests that crystals which display triboluminescence must lack symmetry (in order to permit charge separation) and be poor conductors. However, there are substances which break this rule, and which do not possess asymmetry, yet display triboluminescence anyway. It is thought that these materials contain impurities, which confer properties of asymmetry to the substance. Much of the work done on triboluminescence has been done by Dr. Linda M. Sweeting who is professor of chemistry at Towson University.

Uncompahgre Ute Indians

The Uncompahgre Ute Indians from Central Colorado are one of the first documented groups of people in the world credited with the application of mechanoluminescence involving the use of quartz crystals to generate light. The Ute constructed special ceremonial rattles made from buffalo rawhide which they filled with clear quartz crystals collected from the mountains of Colorado and Utah. When the rattles were shaken at night during ceremonies, the friction and mechanical stress of the quartz crystals impacting together through the translucent buffalo hide produced flashes of light.

See also

• Fractoluminescence
• Piezoelectricity
• Earthquake light

References

• Martín Gil Jesús and Martín Gil Francisco J. "Triboluminescence of new uranyl salts", Journal of Chemical Education, 1978, 55(5):340.