Phonon induced line broadening and population of the dark exciton in a deeply trapped localized emitter in monolayer WSe2

We acknowledge financial support by the State of Bavaria. Y.-M.H. acknowledges support from the Sino-German (CSC-DAAD) Postdoc Scholarship Program. This publication was funded by the German Research Foundation (DFG) and the University of Wuerzburg in the funding programme Open Access Publishing. We study trapped single excitons in a monolayer semiconductorwith respect to their temperature stability, spectral diffusion and decaydynamics. In a mechanically exfoliated WSe2 sheet, we could identifydiscrete emission features with emission energies down to 1.516 eV whichare spectrally isolated in a free spectral range up to 80 meV. The strongspectral isolation of our localized emitter allow us to identify strongsignatures of phonon induced spectral broadening for elevated temperaturesaccompanied by temperature induced luminescence quenching. A directcorrelation between the droop in intensity at higher temperatures with thephonon induced population of dark states in WSe2 is established. While ourexperiment suggests that the applicability of monolayered quantum emittersas coherent single photon sources at elevated temperatures may be limited,the capability to operate them below the GaAs band-edge makes themhighly interesting for GaAs-monolayer hybrid quantum photonic structures. Postprint