Scientists from Shandong University jointly with their colleagues from the Lanzhou Institute of Chemical Physics at the Chinese Academy of Sciences have developed an elastic material that can emit ultraviolet light in response to mechanical stress, such as stretching, friction or bending. This effect makes it possible to generate light directly from movement, without using batteries, wires or an external power source. These self-powered materials could form the basis for a new generation of wearable sensors, smart skin for robots or hidden marking systems, and could even be used to sterilize surfaces with safe ultraviolet light.
In order to create this material, the researchers synthesized the inorganic phosphor Sr₃(BO₃)₂, i.e., strontium bromate doped with praseodymium ions, and uniformly distributed its microparticles in an elastic polymer matrix made of polydimethylsiloxane. The formation of a strong interfacial contact between the phosphor crystals and the polymer was crucial. It is at this interface that contact electrification occurs during mechanical deformation: repeated cycles of contact and separation of the surfaces result in electron transfer, forming a local electric field that excites praseodymium ions and leads to the emission of ultraviolet light.
Experiments showed that the resulting composite emits intense ultraviolet radiation with a peak wavelength of 272 nanometers. This range belongs to the so-called solar-blind ultraviolet, which is virtually absent in natural sunlight and is therefore easily detected even under bright external lighting. In the first tensile cycle, the radiant power density reached about 6.2 mW per square meter. During cyclic tests, the material retained detectable luminescence even after 10,000 strain cycles, indicating high stability of the effect.
The material’s self-healing ability was also important. After the load is removed, the interfacial bonds partially regenerate on their own. With just one second of rest, ultraviolet luminescence intensity goes back to roughly 43% of its original level, reaching approximately 90% after 24 hours. At the same time, the researchers demonstrated that the optimal balance between brightness and durability is achieved with moderate strains of up to 40%. While a higher stretch does produce a brighter initial signal, it also accelerates the degradation of the interface between the phosphor particles and the polymer, reducing the stable operating period.
The scientists are exploring several practical applications for this material. For instance, it could be used in autonomous mechanical load and strain sensors, flexible sensor coatings and smart skin elements for robotics, where it is important to visually monitor stress distribution without using complex electronics.
The solar-blind nature of the radiation makes it a promising material for hidden optical marking and outdoor object tracking. As a demonstration, the researchers attached an elastic film to the wing of a bird model: when flapped, it began to glow under ultraviolet light, making it possible to detect motion reliably even in bright sunlight, which means that it acted as a self-powered optical tag.
Another area of research involves the bactericidal properties of hard ultraviolet light. Experiments have shown that when the film is stretched repeatedly, the generated radiation kills harmful bacteria, including E. coli and staphylococcus. This paves the way for self-cleaning surfaces, such as door handles or medical instruments that self-sterilize upon use.
This work is currently at the research stage. Before these materials can move from laboratory prototypes to engineering devices, it is planned to conduct a series of additional experiments to optimize the interface, increase mechanical durability and quantify the relationship between the load and ultraviolet output power more precisely.
