Triboluminescence

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Triboluminescence is an optical phenomenon in which light is generated when asymmetrical crystalline bonds in a material are broken when that material is scratched, crushed, or rubbed. The phenomenon is not fully understood, but appears to be caused by the separation and reunification of electrical charges. The term comes from the Greek tribein (to rub) and the Latin lumen (light). Triboluminescence can be observed when breaking sugar crystals (especially Wint-O-Green Life Savers) and peeling adhesive tapes.

Triboluminescence is often used as a synonym for fractoluminescence (a term sometimes used when referring only to light emitted from fractured crystals). Triboluminescence differs from piezoluminescence in that a piezoluminscent material emits light when it is deformed, as opposed to broken. These are examples of mechanoluminescence, which is luminescence resulting from any mechanical action on a solid.

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[edit] History

[edit] 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.

[edit] Later descriptions

The first recorded observation occurred is attributed to English scholar Francis Bacon when he wrote in his 1620 Novum Organum 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."[1] The scientist Robert Boyle also reported on some of his work on triboluminescence in 1663. In the late 1790s sugar production began to produce more refined 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.

[edit] 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 recent work on triboluminescence was done by Dr. Linda M. Sweeting who was professor of chemistry at Towson University until her untimely death in September 2003.

[edit] Examples

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.[2] In 1953, Russian scientists showed that triboluminescence caused by peeling a roll of Scotch Tape in a vacuum can produce X-rays.[3] In 2008, Mexican scientists working at UCLA performed an experiment that showed the rays can be strong enough to leave an X-ray image of a finger on dental photographic paper; they hoped to use their research to create a new type of x-ray imaging device.[4] 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. Wint-O-Green Life Savers work especially well for creating such sparks, because wintergreen oil (methyl salicylate) is fluorescent and converts ultraviolet light into blue light. Some Band Aid wrappers and Breathe Right wrappers also glow bluish-green when unwrapped swiftly.

[edit] Fractoluminescence

Fractoluminescence is often used as a synonym for triboluminescence.[5] It is the emission of light from the fracture (rather than rubbing) of a crystal, but fracturing often occurs with rubbing. Depending upon the atomic and molecular composition of the crystal, when the crystal fractures a charge separation can occur making one side of the fractured crystal positively charged and the other side negatively charged. Like in triboluminescence, if the charge separation results in a large enough electric potential, a discharge across the gap and through the bath gas between the interfaces can occur. The potential at which this occurs depends upon the dielectric properties of the bath gas.

This phenomenon can be demonstrated by removing ice from a freezer in a darkened room, under conditions in which the ice makes cracking sounds from sudden thermal expansion. If the ambient light is dim enough, flashes of white light from the cracking ice can be observed.

[edit] See also

[edit] References

  • Martín Gil Jesús and Martín Gil Francisco J. "Triboluminescence of new uranyl salts", Journal of Chemical Education, 1978, 55(5):340.
  1. ^ Bacon, Francis. Novum Organum
  2. ^ Nature (journal). Sticky tape generates X-rays
  3. ^ http://www.nytimes.com/2008/10/28/science/28xray.html?_r=1&partner=rssnyt&emc=rss
  4. ^ http://www.technologyreview.com/blog/editors/22157/
  5. ^ http://goldbook.iupac.org/T06499.html

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Triboluminescence"
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