Photoluminescence enhancement at a high generation rate induced by exciton localization

The photoluminescence (PL) efficiency of two-dimensional (2D) transition metal dichalcogenides (TMDs) is extremely low under high power excitation, limiting its potential in display and light-emission application. This arises from the much shorter lifetime of non-radiative recombination than radiative recombination, wherein photo-carriers tend to decay through non-radiative processes. Herein, a "molecular state" near the valence band is successfully introduced into the ${{\rm MoS}_2}$ monolayer to increase the density of radiative states and speed up the exciton relaxation. This reduces the recombination lifetime of excitons by two orders of magnitude and forms vigorous competition with non-radiative decays. As a consequence, dozens of times enhancement of PL in ${{\rm MoS}_2}$ monolayers under high excitation power (${\rm G}\sim{{10}^{19}}\;{{\rm cm}^{- 2}}\cdot{{\rm S}^{- 1}}$) is realized. These results provide an effective method to improve PL efficiency under high injection levels for applications of 2D materials in light-emission industry.