Effects of Repetitive Pressure on the Photoluminescence of Bare and ZnS-Capped CuInS₂ Quantum Dots: Implications for Nanoscale Stress Sensors

Semiconductor quantum dots (QDs) are promising materials for stress/strain sensing applications owing to their pressure-dependent photoluminescence (PL) and nanoscale size, while the impact of stress and microstructure on their optical properties still awaits in-depth investigations under more realistic loading conditions. Herein, bare CuInS2 QDs and core–shell structured CuInS2/ZnS QDs are investigated under repetitive pressure loadings to elucidate the pressure-dependent PL responses over many pressure cycles. The CuInS2/ZnS QDs not only show higher PL intensity but also exhibit a reliable and simple relationship between PL emission peak energy (EPL) and external pressure (P), which is desirable for actual application in stress/strain sensing. Specifically, the EPL–P relationship of bare CuInS2 QDs changes after the first loading–unloading cycle, while the EPL–P relationship of CuInS2/ZnS QDs shows repeatable trajectories under different cycles. This research provides experimental support for designing QD-based stress/strain sensing materials and explains how the shell and surface microstructure will affect the mechanical-luminescence responses of QDs.