Dual‐Window Broadband Near‐Infrared Mechanoluminescence in MgO‐Based Phosphors

Abstract

ABSTRACT Near‐infrared (NIR) mechanoluminescence (ML) offers a self‐powered and non‐invasive route for stress visualization and biomechanical imaging, yet most NIR ML materials remain constrained by narrow emission bandwidths and reliance on dark‐field conditions. Here, we report two complementary MgO‐based ML systems spanning the NIR‐I and NIR‐II windows, establishing MgO as a robust platform for broadband mechanoresponsive emission. MgO:Cr 3+ delivers tunable NIR‐I ML (700–1000 nm; full width at half maximum, FWHM, 94–188 nm) under diverse mechanical stimuli, including friction, impact, tension, compression, bending, and twisting, while MgO:Ni 2+ produces ultrabroadband NIR‐II ML (1000–1700 nm; FWHM 225 nm) readily detectable under ambient lighting. Mechanistic studies reveal that ML arises from the synergistic interplay of local piezoelectric polarization, dislocation‐mediated charge separation, and triboelectric effects at organic–inorganic interfaces, whereas the observed spectral variations stem from crystal‐field modulation and lattice distortions. Co‐doping of Cr 3+ and Ni 2+ further differentiates optical and mechanical excitation pathways—optical excitation induces Cr 3+ ‐sensitized Ni 2+ emission, whereas mechanical excitation directly activates their low‐lying levels. These insights unify mechano‐to‐photon conversion in centrosymmetric oxides and provide design principles for broadband, durable, and environmentally adaptive ML materials, advancing applications in multimodal sensing, structural health monitoring, and noninvasive biomechanical imaging.