How does the light emission mechanism of triboluminescence work? The famous sugar experiment

If you break a piece of sugar, then a barely noticeable bluish light is released. The very fact of such a glow of sugar when it is mechanically damaged was described by Francis Bacon.

Today there are plenty of such experiences on the Internet, and I myself wrote about this phenomenon. If take a transparent glass and chop a piece of sugar on a plate with it, and do the experiment in a dark room, then a small flash will be observed and with great care it can be noticed. This, of course, is not a camera flash, but it is visible.

Phenomenon called triboluminescence. It is characteristic of many crystalline bodies and appears when they are destroyed. Sugar, quartz, mercury in glass and many other materials can exhibit such properties.

Here there is nothing fundamentally new. The phenomenon has been described and discussed many times. But here how to physically explain the process taking place? I couldn’t find any information about this among the many scientific articles. Therefore, let's look at the physics of the process.

Surprisingly, the explanation of the phenomenon is still somewhere at the level of a physical paradox. There is no unanimous opinion about its nature. There are three basic hypothetical explanations and all of them… are considered objective. It turns out that all that remains is to choose the one that you like.

In some cases the phenomenon is explained excitation of photoluminescence by electrical dischargesoccurring during the splitting of a crystalline body, in other cases it is caused movement of dislocations during deformation. The biological phenomenon of triboluminescence is caused by the recombination of free radicals during mechanical activation. Well, my personal professional opinion is release of energy in the form of a quantum of light upon destruction of the structure. Let's go through these ideas.

Photoluminescence excited by electrical discharges

By definition, luminescence is a non-thermal glow of a substance that occurs after it absorbs excitation energy. Accordingly, photoluminescence is a process associated with excitation through visible light or a flow of electrons (aka electrical discharges).

When a material is mechanically damaged, its structure is the first to suffer. The structure in a crystalline body is a group of ordered atoms arranged in some sequence. Atoms include electrons. When damaged, these electrons begin to migrate and charge flow can occur. Such movement can, in some cases, initiate an excited state of the material structure and, after returning to their positions from higher energy levels, the electrons will release energy in the form of a light quantum. This is the phenomenon we observe.

True, complexity arises when it comes to non-metals. There are significantly fewer electrons capable of “running” like this. But we can quite observe the glow under mechanical influence. It turns out that the mechanism of its occurrence may differ from simple excitation by an electrical discharge.

Dislocation movement

Well, this is perhaps the most understandable form of process description for a materials scientist. Dislocation logic is based on the fact that in the crystal structure there are always “deviations” from the correct arrangement of atoms. Let's say 10 atoms will be located along a straight line, and 11 will be slightly shifted. When many such displaced atoms appear, they are arranged in a regular manner and a dislocation is formed. Existence dislocation is perceived by materials scientists as a natural imperfection of any material.

Well, then, if you start, for example, to deform such a body, then dislocations will move and their generalization will lead to the formation of a crack. This is the dislocation theory of fracture.

Along with the movement of a dislocation, not only a crack can form, and also release energy. Energy is released in the form of a quantum of light and this is due both to the interactions of electrons and to the breaking of bonds.

Technically, this mechanism would also be well suited for metal bodies. But it is more difficult to classify it as a non-metal, although it also has a crystalline structure. Traditionally, all dislocation models are attributed specifically to metallic materials.

Maybe everything is even simpler?

Well, I will not try to explain the biological mechanism mentioned above, since I have no knowledge in this area. As I understand it, it all comes down to to the destruction of chemical bonds, which initiates a reaction with the release of light. Something like the glow of a firefly.

My process logic triboluminescence simpler and more difficult at the same time. It is not entirely clear why we should look for some kind of intermediate mechanism.

All of you have probably broken a stick over your knee. In this case, energy is released, which is contained inside the material. The breaking of bonds leads to the initiation of a sound wave. Like the crack of a whip through the air. And here, for some reason, there is no confusion. Mechanical energy initiates vibrations in the medium.

Consider damage to atomic bonds within a crystalline material. Classical physics likes to portray this as a kind of material string between two particles. Communication, of course, contains energy. When it is destroyed, energy will be released into the environment, but in the form of a light quantum. This phenomenon is equivalent to snapping your fingers, but in the case of snapping your fingers, vibrations occur in the air, and in the case of destruction of the structure A “click” occurs in an electromagnetic field. We see it as light.

But according to this logic, any body with mechanical damage… would have to emit visible light. But we observe the phenomenon only in some cases and for some crystalline materials. Probably this specificity related to the number of atoms per unit volume. Which implies a certain number of atomic bonds. I will study this logic in more detail and talk about it in more detail someday.

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