Phosphorescent MoS₂ quantum dots as a temperature sensor and security ink

Currently, few phosphorescent materials (PMs) possess a long phosphorescence lasting time and have potential for application in chemical sensors. Herein, we disclose that the incorporation of few-layer molybdenum disulfide quantum dots (FL-MoS₂ QDs) into poly(vinyl alcohol) (PVA) matrices leads to the emission of bright green phosphorescence with a long lasting time of 3.0 s and a phosphorescence quantum yield of 20%. This enhanced phosphorescence originates from the formation of O-H⋯S hydrogen bonding networks between the rich sulfur sites of the FL-MoS₂ QDs and the hydroxyl groups of the PVA molecules, which not only rigidifies the vibration modes of the FL-MoS₂ QDs but also provides an oxygen barrier. Further investigations reveal that the FL-MoS₂ QD/PVA composites exhibit a longer phosphorescence lasting time than N,S-doped carbon dots, few layer tungsten disulfide quantum dots, Rhodamine 6G, and Rhodamine B in PVA matrices. Since heat efficiently induced the removal of water moisture from PVA matrices, the FL-MoS₂ QD/PVA composites could be implemented for phosphorescence turn-on and naked-eye detection of temperature variations ranging from 30 to 70 °C. By contrast, the carbon dot/PVA composites were incapable of sensing environmental temperature due to their weak hydrogen bonding with the hydroxyl groups of PVA matrices. Additionally, this study reveals the potential of the FL-MoS₂ QD/PVA composites as an advanced security ink for anti-counterfeiting and encryption applications. The given results could open a new direction for potential application of two-dimensional quantum dots in phosphorescence-based sensors and security inks.