Tailoring of Bound Exciton Photoluminescence Emission in WS₂ Monolayers

Temperature- and laser power-dependent photoluminescence (PL) properties of the asymmetric defect-bound exciton band XD in defective WS2 monolayers, grown by chemical vapor deposition, are studied. Based on PL mapping, a monolayer region with an intensive XD band emission at about 1.9 eV is chosen for further studies. The XD band is thermally quenched above 180 K, and the thermal activation energy is found to be Ea = 33 +/- 4 meV. At T= 15 K, the XD band intensity reveals a sublinear dependence with increasing excitation power and the peak position shows a blueshift of about 15 meV per decade of laser power. It is shown that the XD band is related to the deep defect states within the band gap of WS2.