Biaxial strain tuned upconversion photoluminescence of monolayer WS.

Monolayer tungsten disulfide (1L-WS) is a direct bandgap atomic-layered semiconductor material with strain tunable optical and optoelectronic properties among the monolayer transition metal dichalcogenides (1L-TMDs). Here, we demonstrate biaxial strain tuned upconversion photoluminescence (UPL) from exfoliated 1L-WS flakes transferred on a flexible polycarbonate cruciform substrate. When the biaxial strain applied to 1L-WS increases from 0 to 0.51%, it is observed that the UPL peak position is redshifted by up to 60 nm/% strain, while the UPL intensity exhibits exponential growth with the upconversion energy difference varying from - 303 to - 120 meV. The measured power dependence of UPL from 1L-WS under biaxial strain reveals the one photon involved multiphonon-mediated upconversion mechanism. The demonstrated results provide new opportunities in advancing TMD-based optical upconversion devices for future flexible photonics and optoelectronics.