Near infrared mechanoluminescence from Sr3Sn2O7: Nd3+ for in situ biomechanical sensor and dynamic pressure mapping

Mechanoluminescence (ML) is a phenomenon upon external mechanical stimuli and it has found diverse applications such as stress sensing, structure health diagnosis, 3‐D signature, energy harvesting etc because of its unique properties of in situ and real‐time response to the stimuli. However, ML of most of the state‐of‐art phosphors primarily appears within the spectral range from ultraviolet to visible, which does not lie in the biological transparent windows, and, therefore, limits its applications in biological field. Here, we report a strong near infrared (NIR) ML from orthorhombic Cmcm perovskite Sr3Sn2O7: Nd3+, which is peaked at ~ 900 nm and located exactly within the first optical transparent window of tissues. The ML apparates after gradual discharge of the traps deeper than 0.73 eV triggered by the external mechanical stimuli and subsequently excitation of Nd3+ to the state of 4F3/2. The rechargable ML presents well repeatable linearity to loaded force at least up to 5000 N, and it can penetrate tissues easily that are thick up to 30 mm such as pigskin and the ceramic disk of hydroxy apatite which is the main constituent of bone. These results demonstrate the potential application for in situ biomechanical sensor. Meanwhile, by recording and processing these ML signals during signing on a pellet sample, for the first time, we provide a novel signature system based on NIR ML. This could raise the security level of existed signature anti‐countering to a higher level.