  Monolayer transition metal dichalcogenides have emerged as promising
materials for optoelectronic and nanophotonic devices. However, the low
photoluminescence (PL) quantum yield (QY) hinders their various potential
applications. Here we engineer and enhance the PL intensity of monolayer WS2 by
femtosecond laser irradiation. More than two orders of magnitude enhancement of
PL intensity as compared to the as-prepared sample is determined. Furthermore,
the engineering time is shortened by three orders of magnitude as compared to
the improvement of PL intensity by continuous-wave laser irradiation. Based on
the evolution of PL spectra, we attribute the giant PL enhancement to the
conversion from trion emission to exciton, as well as the improvement of the QY
when exciton and trion are localized to the new-formed defects. We have created
microstructures on the monolayer WS2 based on the enhancement of PL intensity,
where the engineered structures can be stably stored for more than three years.
This flexible approach with the feature of excellent long-term storage
stability is promising for applications in information storage, display
technology, and optoelectronic devices.
