  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.
