Self-powered near-infrared mechanoluminescence through MgO/MgF₂ piezo-photonic heterojunctions

Near-infrared mechanoluminescent (NIR ML) materials attract considerable attention for their force-to-light conversion capabilities. However, current materials generally have disadvantages such as high threshold and poor self-recovery ability, which limit their practical applications. Herein, we present a self-powered NIR ML material MgF₂:Cr³⁺, which does not require pre-charging process. Leveraging the structural similarity between MgF₂ and MgO, we design a MgO/MgF₂:Cr³⁺ heterojunction piezo-photonic system that exhibits high intensity, low activation threshold, and excellent self-powered ML performance. By tuning the molar ratio of MgO to MgF₂, the optimized ML intensity enhances by ≈18 times. Kelvin probe force microscopy surface potential measurement reveals a significant built-in electric field at MgF₂:Cr³⁺ heterojunction interface. Based on the first-principle calculation results, the excellent ML performance originates from the offset of the valence band and the conduction band in the MgO/MgF₂:Cr³⁺ heterostructure and the narrowing of the band gap, which significantly improve the electron (4.09 × 10²cm²V^-1 s^-1) and hole (4.62 × 10²cm²V^-1 s^-1) mobility, thereby boosting charge transfer and recombination processes. This study provides a strategy for designing high-performance self-powered NIR ML materials based on interfacial effects, offering insights into their expanded applications in the potential bio stress related biological field.