Exciton dynamics in tungsten dichalcogenide monolayers.

The strong photoluminescence from monolayer WS and WSe paves the way for a range of optoelectronic applications and opens up the door for ultrafast carrier dynamics study. In this work, we observed that monolayer WS and WSe exhibited giant absorption in the visible frequency range. This phenomenon has been ascribed to the band nesting effect. We used time-resolved photoluminescence spectroscopy to study the absorption and recombination dynamics of the photocarriers in monolayer WS and WSe. We found that some of the electron-hole pairs excited in the band nesting region initially relaxed to the K/K' point and then underwent radiative decay. The decay and recombination of the photocarriers occurred rapidly and terminated within the sub-nanosecond timescale. The observed experimental results indicate the great potential of these materials in optoelectronic devices.