Multimodal optical sensing based on a Sm3+-activated Sr3Sn2O7 phosphor: stress visualization and temperature monitoring

Conventional mechanoluminescent (ML) materials are limited to stress sensing, restricting their application in integrated optical sensing. In this study, we develop a multimode-emitting phosphor, Sr_2.996(Sn_1.75Ge_0.25)O_7.002:0.004Sm³⁺, which exhibits simultaneously excellent ML properties through defect engineering of the host matrix and non-contact temperature sensing capability based on the fluorescence intensity ratio (FIR). The incorporation of Li⁺ boosts the ML intensity by approximately 4-fold, resulting in an ML signal 30 times stronger than its persistent luminescence (PersL). The enhancement drastically suppresses the PersL interference during stress sensing. Furthermore, the phosphor exhibits a high relative temperature sensitivity of 1.48% K⁻¹ at 303 K. Experimental characterization and first-principles calculations elucidate the mechanism behind the ML enhancement. Multifunctional phosphors, capable of simultaneous non-contact stress and temperature sensing, have significant potential for application in advanced optical sensing systems, particularly in high-temperature, high-pressure machinery monitoring, and are expected to find practical applications in industrial monitoring, biomedical devices, aerospace and deep-water exploration.