Exciton-to-trion conversion in monolayer WS2 under pressure

Exciton-to-trion conversion in two-dimensional semiconductors defines the transition from an optoelectronics based on neutral bosons to one based on charged fermions, with a huge impact on the transport and spin/valley-related properties. This process has been successfully induced in field-effect transistors under gate voltage, chemically doped samples, and nonuniformly nanoscale-strained materials. Here, we study the evolution of the photoluminescence spectrum of monolayer WS2 under high pressure, decoupling exciton and trion contributions by their responses to laser-power variations. We demonstrate that crystal compression drives a substrate-independent, partially reversible exciton-to-trion conversion, with trion recombination dominating the emission above 3 GPa. The observed mechanism does not rely on external charge injection but involves the pressure evolution of intrinsic doping levels within the band structure. Our results indicate that trion-based emission can be achieved by reshaping the periodic crystal potential via the modulation of interatomic interactions, offering a novel approach to the study of exciton-to-trion conversion in two-dimensional materials.