Intralayer Excitons in Graded Alloys of Mo_xW_1-xS₂ Monolayers compared to pristine MoS₂, and WS₂

We employed an additive-assisted synthesis technique to prepare single-crystalline monolayers of alloyed Mo_xW_1-xS₂ and investigated their optical properties at the nanoscale. The monolayer has tunable band gaps in a broad range of 1.70–2.05 eV displaying prominent variations in sulfur composition from the center to the edge regions. The existence of excitons, trions, and defect-bound excitons are investigated using power-dependence and temperature-dependent (4 K−300 K) photoluminescence spectroscopy. Detailed analysis of the alloyed monolayer reveals evidence of new types of defect-bound excitons originating at low temperatures compared to pristine MoS₂ and pristine WS₂