The study investigates electroluminescence in single-layer molybdenum disulfide (MoS₂) field-effect transistors (FETs) built on transparent glass substrates. By comparing absorption, photoluminescence, and electroluminescence, the researchers find that all these processes involve the same excited state at 1.8 eV. The electroluminescence exhibits pronounced threshold behavior and is localized at the contacts. The results suggest that single-layer MoS₂, a direct band gap semiconductor, has potential for novel optoelectronic devices such as 2D light detectors and emitters. The study also highlights the importance of improving electrostatic gating techniques to enhance the efficiency of light emission and detection in MoS₂-based devices.The study investigates electroluminescence in single-layer molybdenum disulfide (MoS₂) field-effect transistors (FETs) built on transparent glass substrates. By comparing absorption, photoluminescence, and electroluminescence, the researchers find that all these processes involve the same excited state at 1.8 eV. The electroluminescence exhibits pronounced threshold behavior and is localized at the contacts. The results suggest that single-layer MoS₂, a direct band gap semiconductor, has potential for novel optoelectronic devices such as 2D light detectors and emitters. The study also highlights the importance of improving electrostatic gating techniques to enhance the efficiency of light emission and detection in MoS₂-based devices.