UV/NUV and BW‐I Mechanoluminescence from Bi‐Activated CaY ₂ Ge ₄ O ₁₂ Polycrystals

Abstract Mechanoluminescent (ML) materials emitting in the near‐ultraviolet (NUV) and near‐infrared (NIR) spectral regions are of interest across various fields, including stress sensing, advanced labelling technology and bio‐imaging. However, the majority of current ML materials is found to emit light in the visible region, while those in the NUV/NIR spectral range remain relatively rare. Here, a series of polycrystalline bismuth‐doped CaY ₂ Ge ₄ O ₁₂ is presented as an NUV/NIR‐ML material for the first time. Making use of the simultaneous presence of multiple bismuth species in a single host, multi‐modal luminescence is achieved, enabling simultaneous emission in the ultraviolet‐A region and tissue‐penetrating near infrared region. Bi doped CaY ₂ Ge ₄ O ₁₂ shows multi‐mode luminescence in first biological window (BW‐I; 700–950 nm) and second biological window (BW‐II; 1050–1300 nm), under optical and mechanical stimulation. The composites prepared by embedding such phosphor into different elastic matrices exhibit stable ML under mechanical stimulation, confirming the phosphor's compatibility with diverse encapsulation media for potential 3D printing. The designed ML material can hold potential applications for stress sensing, UV‐emitting scaffolds, biomedical imaging, and anti‐counterfeiting applications.