Mechanically Induced Light Emission and Infrared-Laser-Induced Upconversion in the Er-Doped CaZnOS Multifunctional Piezoelectric Semiconductor for Optical Pressure and Temperature Sensing

In this study, we report an Er-doped quaternary piezoelectric semiconductor CaZnOS:Er³⁺ which shows both mechanoluminescence and upconversion luminescence properties. Under mechanical stimulation, green light emission can be observed by the naked eye from a flexible film fabricated by encapsulating CaZnOS:Er³⁺ particles between two polyethylene glycol terephthalate substrates. The integral emission intensity is proportional to applied pressure, making CaZnOS:Er³⁺ suitable for dynamic pressure sensing applications. Moreover, the doped sample also shows bright visible emission with near-infrared (980 nm) excitation. The fluorescence intensity ratio between two upconversion emission bands corresponding to ²H_11/2, ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ is sensitive to the variation of temperature. As a multifunctional optical material, CaZnOS:Er³⁺ could be used to not only visualize two-dimensional pressure distribution, through mechanically induced emission, but also sense temperature via the upconversion (UC) luminescence. This work provides a novel kind of multifunctional luminescent material for the development of integrated and coupling devices.