Tunable Exciton Radiative Recombination Lifetime in Twisted Bilayer Molybdenum Disulfide

The ability to control exciton radiative recombination dynamics is a promising element for expanding applications of atomically thin two-dimensional (2D) materials. Here, we show that twist angle can be used to control the interlayer indirect exciton dynamics of transition-metal dichalcogenide bilayers by changing the indirect band gaps in the two layers. Exciton radiative recombination lifetimes of twisted MoS2 bilayers are monitored by fluorescence lifetime imaging microscopy (FLIM) technology. Interestingly, interlayer twists cause only a weak change of direct excitons, but greatly modify the indirect exciton recombination channel due to the repulsive steric effects. Thus, the indirect exciton radiative recombination lifetime first increases from 5.2 to 27.0 ns with twist angle (θ) changing from 0 to 30° (more than 5-fold), and then decreases to 8.3 ns with θ further increasing to 60°. Our work paves a new route for engineering exciton radiative recombination dynamics of 2D materials, which can improve the future applications of optoelectronic devices based on 2D materials.