Long Non-Exponential PL Decay from Localized Defect States in Monolayer WSe$_2$ at Low Temperature

We investigate the recombination dynamics of localized defect emission in monolayer WSe$_2$ using time-resolved photoluminescence over the temperature range from 4 to 120 K. The defect emission comprises a dominant sub-nanosecond exponential component and two weak, long-lived power-law channels extending from a few nanoseconds to several hundred nanoseconds. The power-law relaxation admits an interpretation in terms of continuous distributions of recombination lifetimes associated with an inhomogeneous ensemble of localized states. Temperature-dependent measurements were performed to examine the thermal detrapping mechanisms governing these long-lived channels. Spin-resolved electronic-structure and optical-transition calculations provide microscopic insight into the localized states and the available recombination pathways. These results provide a framework for understanding long-lived, non-exponential defect recombination in two-dimensional semiconductors.