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he light emission lifetime from a family of perovskite-like tin halides depends strongly on temperature, researchers reported in the journal Nature Materials (doi:10.1038/s41563019-0416-2). They used the materials to make a high-resolution remote thermal imaging device. Thermal imagers are used in medicine, defense, and security cameras and to inspect buildings and pipelines. Conventional devices detect infrared

Nacre-inspired composites display optical transparency, fracture toughness

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nspired by the structure of mother of pearl (nacre), researchers from ETH Zürich have demonstrated an approach to fabricating optically transparent composite materials that are tough, strong, and wear-resistant—normally an elusive combination. As they reported in Nature Communications (doi:10.1038/s41467019-10829-2), the composites have some of the highest strengths among glasses and a fracture toughness up to three times greater than that of common glasses. Optically transparent materials such as silica- and soda-lime glasses are strong enough to withstand heavy loads, but they are prone to shattering—cracks spread quickly due to their brittle nature. Chemical and thermal treatments can increase the strength of a material but not its resistance to crack propagation, a property associated with fracture toughness. Recently, research has demonstrated that engraving microstructures on a brittle glass surface can increase its fracture toughness, but the microstructures act as defects that reduce the material’s strength. Led by André R. Studart and Florian Bouville (now at Imperial College London), the ETH team took a natureinspired approach to designing a material that is tough yet strong. The inside of mollusk shells and the outside of pearls are composed of nacre, a strong, tough, iridescent material. This combination of properties is achieved via a two-pronged

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radiation from objects. But another promising approach is to use temperature-sensitive photoluminescent materials that emit visible light. These materials can be integrated into objects as temperature probes. To measure the object’s temperature, the material is hit with laser pulses, and then the temperature-dependent photoluminescent decay is measured. These emitters need to be thermally sensitive (less than 0.1°C) over a large temperature range.

After testing several tin halide perovskite compounds, ETH Zürich’s Sergii Yakunin and Maksym V. Kovalenko and their colleagues shortlisted three materials with suitable thermographic properties. The materials could reproducibly measure temperature down to 0.013°C over a range of 100°C. Using low-cost hardware for fluorescence lifetime imaging, the research team was able to use one of the perovskites (C4N2H14I)4SnI6 to make a sensitive, real-time thermal recording.

approach: a chemical a b composition that offers optical functionality and a complementary microscale architecture that adds toughness to an otherwise brittle material. Studart calls this approach “a pathway to combine, in a single composite ma1 cm 1 cm terial