Formation and influence of the K–Q trion state

Determine the formation process of the K–Q trion and characterize the influence of this high-energy state on the observed exciton complexes in a WS₂ monolayer.

Background

The paper models temperature-dependent photoluminescence kinetics in a negatively doped WS₂ monolayer using coupled bright, dark, trion, and charged-biexciton populations. The authors identify a middle-lived component in the bright-trion kinetics that may arise from population transfer involving a higher-energy Q-valley state.

They estimate a phonon energy consistent with the energy difference between excitons in the K–K′ and K–Q valleys. Although prior theoretical work suggests that phonon-mediated transitions involving these states may be slower than direct intravalley relaxation, the paper explicitly leaves unresolved both how the K–Q trion forms and how the high-energy state affects the observed exciton complexes.

References

One of the possible mechanisms responsible for the middle lifetime may be unaccounted population transfer involving the higher-energy $Q$-valley state. The obtained value of $\Delta_{ph}$ also agrees well with the energy difference between excitons in the $K-K'$ band and the $K-Q$ band . According to recent theoretical studies , the transition between these excitons via the phonons should be significantly slowed down compared to the direct intravalley transition in comparison with intravalley $K-K'$ relaxation through the $K_3$ phonon. However, the formation process of the $K-Q$ trion remains unclear, and the influence of this high-energy state on the observed exciton complexes is still debated.

— Self-balancing luminescence kinetics of charged excitons in WS$_2$ monolayer  (2609.17289 - Veretennikov et al., 15 Sep 2026) in Section “Analysis and discussion,” subsection “Trion $X^-$ kinetics”