Single Photon Emission from Deep Level Defects in Monolayer WSe2

We report an efficient method to observe single photon emissions in monolayer WSe2 by applying hydrostatic pressure. The photoluminescence peaks of typical two-dimensional (2D) excitons show a nearly identical pressure-induced blue-shift, whereas the energy of pressure-induced discrete emission lines (quantum emitters) demonstrates a pressure insensitive behavior. The decay time of these discrete line emissions is approximately 10 ns, which is at least one order longer than the lifetime of the broad localized (L) excitons. These characteristics lead to a conclusion that the excitons bound to deep level defects can be responsible for the observed single photon emissions.