Synthesis of ZnS:Mn2+@Al2O3 core–shell mechanoluminescent materials and the multimodal mechanical sensing performance

Abstract

Conventional ZnS:Mn²⁺ mechanoluminescent materials suffer from low emission efficiency due to non-radiative recombination at surface dangling bonds and defects, alongside poor interfacial stress transfer within polymer matrices. Herein, a ZnS:Mn²⁺@Al₂O₃ core–shell architecture is designed via interfacial engineering to achieve a synergistic breakthrough in surface passivation and efficient stress conduction. Polyhedral ZnS:Mn²⁺ cores were synthesized via a high-temperature solid-state method, followed by controlled liquid-phase deposition of an alumina precursor in an acetate buffer system and subsequent calcination at 300 °C to yield core–shell composites with varying coating gradients (5–20 wt%). The phase structure, micro-morphology, and interfacial chemical bonding of the pure core–shell powders were systematically characterized via X-ray diffraction (XRD), scanning electron microscopy – energy dispersive spectroscopy (SEM-EDS), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). A synchronized opto-mechanical system evaluated their ML performance in polyurethane (PU) and epoxy matrices under tensile, compressive, and friction modalities. Results demonstrate conformal Al₂O₃ encapsulation. At the optimal 10 wt% coating, tensile ML intensity in PU increased 3.48-fold, while compressive and tribo-ML intensities in epoxy improved by 1.81-fold and 1.21-fold, respectively. Relying on a physical hybrid model, this moderate Al₂O₃ layer efficiently repairs surface defects and maximizes interfacial strain-energy coupling via its high modulus. Conversely, an excessively thick shell induces a detrimental stress shielding effect. Exhibiting excellent linear sensing responses (R² > 0.96) under multimodal loading, this system offers a robust paradigm for high-sensitivity structural health monitoring.