Carrier relaxation to quantum emitters in few-layer WSe2

We present a detailed study of the time-resolved photoluminescence of narrow-line emission centers in WSe2 monolayers and bilayers. Our experiments reveal noninstantaneous photoluminescence intensity rise after the laser pulse. This shows that the simplest excitation model in which the localized states are directly populated by free excitons is not sufficient to fully reproduce experimental results. We, therefore, analyze a more complex phenomenological model where the relaxation of the carriers is mediated by long-lived intermediate states. Strong suppression of the lifetime of those intermediate states at elevated temperatures reveals their unique character, not matching any relaxed excitonic state in WSe2 monolayer.