Near infrared mechanoluminescence from the Nd3+ doped perovskite LiNbO3:Nd3+ for stress sensors

Mechanoluminescence (ML) from most state-of-the-art phosphors primarily appears within the spectral range of ultraviolet to visible and does not lie in the biological transparency windows, therefore limiting its application in biological fields. In this study, we report a novel Nd3+ doped LiNbO3 phosphor, which demonstrates intense and elastic near infrared (NIR) ML under compressive forces. The ML intensity increases with force from 500 to 2500 N, and it remains stable under larger forces due to the failure of the resin. Both the starting and stopping of force loading are found to trigger ML, but the intensity is weakened over time. Meanwhile, this ML emission, peaking at 895 nm, is located within the first biological transparency window range (650–950 nm), and it has been proved to penetrate tissue thicker than 20 mm. This, therefore, extends ML into the NIR range and makes it possible to detect biomechanical behavior in situ inside living bodies.