Generating Room Temperature Defect Bound Excitons in Vanadium Doped WS 2 Monolayers

ABSTRACT Defect‐localized excitons in monolayer transition‐metal dichalcogenides like WS 2 , have attracted enormous interest due to their vast applications in optoelectronics and quantum technologies. Although chemically doped monolayers exhibit a defect‐bound exciton, this distinct feature has preliminary been observed at cryogenic temperatures. Here, we report a prominent defect‐bound excitonic state at room temperature (RT), about 130 meV below the characteristic exciton emission line, in Vanadium‐doped WS 2 (V‐WS 2 ) monolayers. Temperature‐dependent differential reflectance spectra reveal the presence of defect‐bound excitons from 4 K to room temperature. Furthermore, with increasing V‐concentration, a gradual increase in binding energy is observed, from 106 meV at 1.2 wt.% V‐WS 2 to 130 meV at 4 wt.% V‐WS 2 in photoluminescence (PL). Temperature‐dependent PL studies show the sharpening of defect‐emission at low temperatures, from ∼45 nm at RT to ∼3 nm at 4 K. The time‐resolved PL spectra reveal the increased PL decay lifetimes from 30 ± 0.4 ps in pristine WS 2 to 38 ± 0.6 ps in V‐WS 2 at 20 K temperature, confirming the trap‐states. We find that V‐doping induces localized excitons, and increasing the vanadium concentration enhances the Coulomb interaction, stabilizing the defect emission at RT.