Characterization and luminescence properties of CaMgGe₂O₆: Mn²⁺ NIR-I mechanoluminescence phosphor

In recent years, materials exhibiting multimodal luminescence properties from deep red to near-infrared (NIR) wavelengths have been a focal point of research, particularly in the exploration of applications within the realms of stress sensing and dynamic signature anti-counterfeiting. A pyroxene-type layered crystal structure compound, CaMgGe₂O₆: Mn²⁺, has been reported as a mechanoluminescent (ML) material. Upon incorporation into the host, Mn²⁺ ions preferentially substitute for Mg²⁺ ions, emitting deep red to near-infrared light (600–800 nm) within this six-coordinated [MgO₆] octahedral environment. The congruence of photoluminescence and ML spectra indicates that both types of luminescence originate from the same emissive center. The doping of Mn²⁺ ions introduces impurity band, effectively reducing the optical band gap, as evidenced by ultraviolet diffuse reflectance measurements. Thermoluminescence results reveal three defect centers within the phosphor, whose concentrations decrease with Mn²⁺ doping, correlating with a reduction in ML intensity. The ML mechanism of the phosphor is elucidated through the analysis of local piezoelectric properties within the crystal. Overall, this study may pave new pathways for the development of efficient near-infrared mechanoluminescent materials, showcasing potential applications within the biological domain.