  Photoluminescence (PL) of transition metal dichalcogenide (TMD) monolayers is
strongly influenced by the dielectric environment. The defect states present in
the substrate induces uncontrollable doping in the TMD monolayer and thereby
modifies the PL spectra. There have been enormous efforts to tune and overcome
the effect of inevitable subtract defects in PL spectra, but a proper
understanding and a convenient way are still lacking. Here, we systematically
studied the effect of surface defects by gradually increasing the separation
between WS2 monolayer and substrate. Hence, we could precisely modulate the
exciton and trion contribution in the PL spectra of WS2. The excitation power
dependant measurements on dielectric engineered and patterned substrates helped
us to shed light on the mechanism of PL modulation in monolayer WS2. We have
also studied the influence of the nature of the charge carried by substrate
defects on the PL spectra. These results open a new pathway to modulate and
obtain the desired PL spectra of TMDs by engineering the substrates. Our
findings will be useful for fabricating excitonic interconnects, valleytronic,
and single-photon devices.
