September 29, 2022

Researchers created a new glass ceramic that emits light in response to mechanical stress. The highly transparent material is made of a potassium germanate glass matrix embedded with chromium-doped zinc gallate (ZGO) crystals that give the material its mechanoluminescent properties. Credit: Lothar Wondraczek, Friedrich Schiller University Jena

Researchers have created a new glass-ceramic that emits light in response to mechanical stress, a property known as mechanoluminescence. With further development, the new material could be used to create a light source that is turned on by mechanical stress. This can be useful for monitoring tension in artificial joints in the body or providing warnings of dangerous tensions or fractures in buildings, bridges and other structures.


“Most materials that exhibit mechanoluminescence are made as powders, which are not very versatile,” said study team leader Lothar Wondraczek of Friedrich Schiller University Jena in Germany. “We designed a glass-ceramic with mechanoluminescence, which allows the use of glass-like processing approaches to form virtually any shape — including fibers, beads or microspheres — that can be processed into various components and devices.”

The research is reported in a special issue of Optical Materials Express commemorating the United Nations’ International Year of Glass 2022, which celebrates the vital role glass plays in society.

The new highly transparent glass ceramic is made of chromium-doped zinc gallate (ZGO) crystals embedded in a potassium germanate glass matrix. These crystals give the material its mechanoluminescent properties, but are so small that they do not significantly affect the visual transparency of the glass.

“Our work could help make mechanoluminescent materials widely used in a variety of applications, including light-emitting product labels and security codes,” Wondraczek said. “It also ties in well with the International Year of Glass by demonstrating the wide versatility and unexpected properties of glass-like materials.”

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A more practical material

In addition to being difficult to mold into various geometries, mechanoluminescent powders require additional processing steps such as encapsulation in a matrix material. To make a more practical material, the researchers turned to glass ceramics.

Glass ceramic is a relatively new type of material that consists of a crystalline material embedded in a glass matrix. The crystals can be used to give these materials very specific properties, while the glass matrix allows them to be formed using many of the same processes used for glass.

The researchers created the mechanoluminescent glass ceramic by developing an exceptionally fast and stable crystallization process that allows the small ZGO crystals to homogeneously precipitate in the glass after it has been formed. They showed that the materials emitted light under mechanical stress by using the ball drop test, a standard way of imparting a known impact force to a material. “We found that the mechanoluminescence response was reproducible and rechargeable and that it showed a direct correlation with the impact energy,” Wondraczek said.

Now that they have demonstrated the light-emitting properties of the material, they plan to adapt the glass composition so that it can be formed into microscale plate-like objects, optical fibers and spherical spheres, and then explore how these can be used in components and devices. They are also intended to exploit other characteristics commonly attributed to glass-ceramics, such as thermal, chemical and mechanical stability, to extract new functions from the glass-like materials.


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More information:
Jiangkun Cao et al, Mechanoluminescence of highly transparent ZGO:Cr spinel glass ceramics, Optical Materials Express (2022). DOI: 10.1364/OME.459185