External control of optical excitations is key for manipulating light–matter coupling and is highly desirable for photonic technologies. Excitons in monolayer semiconductors emerged as a unique nanoscale platform in this context, offering strong light–matter coupling, spin–valley locking and exceptional tunability. Crucially, they allow electrical switching of their optical response due to efficient interactions of excitonic emitters with free charge carriers, forming new quasiparticles known as trions and Fermi polarons. However, there are major limitations to how fast the light emission of these states can be tuned, restricting the majority of applications to an essentially static regime. Here we demonstrate switching of excitonic light emitters in monolayer semiconductors on ultrafast picosecond time scales by applying short pulses in the terahertz spectral range following optical injection. The process is based on a rapid conversion of trions to excitons by absorption of terahertz photons inducing photodetachment. Monitoring time-resolved emission dynamics in optical-pump/terahertz-push experiments, we achieve the required resonance conditions as well as demonstrate tunability of the process with delay time and terahertz pulse power. Our results introduce a versatile experimental tool for fundamental research of light-emitting excitations of composite Bose–Fermi mixtures and open up pathways towards technological developments of new types of nanophotonic device based on atomically thin materials.

光学激发的外部控制是操纵光与物质耦合的关键，也是光子技术非常需要的。在这种背景下，单层半导体中的激子成为一种独特的纳米级平台，提供强光-物质耦合、自旋谷锁定和卓越的可调谐性。至关重要的是，由于激子发射体与自由电荷载流子的有效相互作用，它们允许对其光学响应进行电切换，形成称为三重子和费米极化子的新准粒子。然而，这些状态的光发射的调节速度存在重大限制，将大多数应用限制在基本静态的状态。在这里，我们通过在光注入后应用太赫兹光谱范围内的短脉冲，演示了单层半导体中激子光发射器在超快皮秒时间尺度上的切换。该过程基于通过吸收太赫兹光子诱导光脱离而将三重子快速转化为激子。通过监测光泵/太赫兹推动实验中的时间分辨发射动力学，我们实现了所需的谐振条件，并证明了该过程随延迟时间和太赫兹脉冲功率的可调性。我们的研究结果为复合玻色-费米混合物的发光激发的基础研究引入了一种多功能实验工具，并为基于原子薄材料的新型纳米光子器件的技术开发开辟了道路。