Optical properties tuned by alloying in monolayer MoWS₂ with graded composition

We investigated the optical and photocarrier properties of monolayer MoWS 2 alloys with graded composition. The samples were synthesized via a two-step chemical vapor deposition method. Photoluminescence spectroscopy revealed a composition-tunable optical bandgap, while the evolution of the trion binding energy demonstrated a pronounced doping effect across the alloy. Power-dependent photoluminescence and transient absorption measurements indicated a significant reduction in exciton–exciton annihilation in the alloy by an order of magnitude, illustrating strong exciton localization. These findings highlight the critical influence of doping and localization effects in determining the photocarrier and optical properties of transition metal dichalcogenide (TMD) alloys. The suppression of exciton–exciton annihilation results in a power-independent photoluminescence quantum yield, suggesting these alloys as promising candidates for optoelectronic applications under high excitation conditions, surpassing the performance limitations of pristine transition metal dichalcogenides.