Tip-induced dynamic control of exciton-trion interconversion at the nanoscale in two-dimensional semiconductors

As two-dimensional (2D) semiconductor devices demand ever higher performance and tunable photo-energy responses, the ability to probe and control exciton-trion interconversion has attracted much attention. However, conventional optical studies predominantly rely on far-field schemes, which suffer from inherent limitations, such as low spatial resolution and weak photoluminescence signals, restricting practical applications. To address these challenges, plasmonic structures have been employed to enhance local electromagnetic fields, facilitating more efficient exciton-trion interconversion in 2D transition metal dichalcogenides. Furthermore, tip-enhanced approaches have expanded the frontiers of excitontrion study by enabling nanoscale spatial resolution and various modulation capabilities, under active cavity configuration. This review article addresses the critical challenge of probing and controlling exciton-trion interconversion. It provides a comprehensive overview of current techniques, spanning far field spectroscopy, plasmonic enhancement, and tip based methodologies, including both foundational strategies and emerging advanced modulation schemes. By summarizing recent developments in this field, this work aims to outline future directions for harnessing photonic quasi particles to advance next-generation optoelectronic and quantum technologies.