Achieving Tunable Mechanoluminescence in CaZnOS:Tb³⁺, Sm³⁺ for Multicolor Stress Sensing

Mechanoluminescent (ML) materials can exhibit visible-to-near-infrared mechanoluminescence when responding to the fracture or deformation of a solid under mechanical stimulation. Transforming mechanical energy into light demonstrates promising applications in terms of visual mechanical sensing. In this work, we synthesized the phosphor CaZnOS:Tb³⁺, Sm³⁺, which exhibited intense and tunable multicolor mechanoluminescence without pre-irradiation. Intense green ML materials were obtained by doping Tb³⁺ with different concentrations. Tunable multicolor mechanoluminescence (such as green, yellow-green, and orange-red) could be realized by combining green emission (about 542 nm), attributed to Tb³⁺, and red emission (about 600 nm) generated from the Sm³⁺ in the CaZnOS substrate. The tunable multicolor ML materials CaZnOS:Tb³⁺, Sm³⁺ exhibited intense luminance and recoverable mechanoluminescence when responding to mechanical stimulation. Benefiting from the excellent ML performance and multicolor tunability in CaZnOS:Tb³⁺, Sm³⁺, we mixed the phosphor with PDMS and a curing agent to explore its practical application. An application for visual mechanical sensing was designed for handwriting identification. By taking a time-lapsed shot while writing, we easily obtained images of the writer's handwriting. The images of the ML intensity were acquired by using specific software to transform the shooting data. We could easily distinguish people's handwriting through analyzing the different ML performances.