Defect and strain effects on photoluminescence and lifetime of monolayer WS₂ and WSe₂

Defect and strain engineering is critical for tailoring the electronic and optical properties of two-dimensional semiconductors for optoelectronics and quantum photonics applications. In this work, atomic defects are created in monolayer WS₂ and WSe₂ using various particle irradiation, including electron, proton, and helium ion. Strain perturbations are introduced by nanopillars patterned on silica substrates. The effects of defects and strain on photoluminescence (PL) and its dynamics are comprehensively investigated at room and cryogenic temperatures. Irradiation of heavy particles or high dose generates high density of defects, where the low-energy defect-bound excitons exhibit long recombination lifetime of several hundred nanoseconds at cryogenic temperatures. Moreover, the power dependence of the defect-bound exciton and localized exciton can be modulated by irradiation dose and particle. Redshifted PL spectra with a 6-21% enhancement in the trion intensity and an increase in the long decay component of lifetime are observed at the strained regions, indicating an efficient funneling effect. The results indicate that irradiation-induced defects and site-controlled strain are effective and highly beneficial for controllable and high-efficiency quantum optical applications.