Enhancement of Exciton Emission from Multilayer MoS₂ at High Temperatures: Intervalley Transfer versus Interlayer Decoupling

It is very important to obtain a deeper understand of the carrier dynamics for indirect-bandgap multilayer MoS₂ and to make further improvements to the luminescence efficiency. Herein, an anomalous luminescence behavior of multilayer MoS₂ is reported, and its exciton emission is significantly enhanced at high temperatures. Temperature-dependent Raman studies and electronic structure calculations reveal that this experimental observation cannot be fully explained by a common mechanism of thermal-expansion-induced interlayer decoupling. Instead, a new model involving the intervalley transfer of thermally activated carriers from Λ/Γ point to K point is proposed to understand the high-temperature luminescence enhancement of multilayer MoS₂. Steady-state and transient-state fluorescence measurements show that both the lifetime and intensity of the exciton emission increase relatively to increasing temperature. These two experimental evidences, as well as a calculation of carrier population, provide strong support for the proposed model.