Nonstoichiometry induced broadband tunable photoluminescence of monolayer WSe2

A nonstoichiometric process by modulating the W/Se atomic ratio was employed to tune the excitonic PL band of monolayer WSe2 from 810 nm to 690 nm. DFT calculations indicate that Se-rich conditions reduce the band gap, while Se-deficient conditions facilitate the increasing band gap and decreasing excitionic binding energy, which finally induces such broadband tuning of the PL band.