Greatly Enhanced Radiative Recombination at High Exciton Density in Acid-Treated 2D Alloy

Enhanced photoluminescence (PL) in transition metal dichalcogenides (TMDs) is critical for their application in optoelectronics. In this study, we report a 99 × PL enhancement in a superacid bis(trifluoromethane) sulfonimide (TFSI)-treated MoS_{2(1-<i>x</i>)}Se_2<i>x</i> alloy. The alloy's optical bandgap is tunable by changing its stoichiometry, allowing for PL enhancement at tailored positions. The PL enhancement is robust even at high excitation power, overcoming the limitation of exciton-exciton annihilation observed in MoS₂. Through molecular dynamics simulations and spectroscopic analysis, we demonstrate that the MoS_{2(1-<i>x</i>)}Se_2<i>x</i> monolayer inherently exhibits moderate strain, which shifts the van Hove singularity in the S-rich domain. Furthermore, density functional theory calculations reveal the absence of a pronounced van Hove feature in the alloy configuration. Our findings extend the range of materials amenable to superacid treatment and open new avenues for optoelectronic applications, particularly those requiring high excitation powers.