Thermally Activated Dark States and Temperature-Dependent Carrier Dynamics in Ultrasmall Ge1-xSnx Colloidal Quantum Dots

Ge1-xSnx alloy quantum dots (QDs) are an attractive class of Group IV nanoemitters, yet the effects of composition and quantum confinement on carrier and recombination dynamics in the ultrasmall regime (<∼2 nm) remain poorly understood. Here, detailed temperature-dependent optical characterization is reported for ultrasmall colloidal Ge1-xSnx QDs with Sn compositions up to 23.6%. Steady-state and time-resolved photoluminescence indicate preservation of a larger fraction of 10 K radiative intensity and rate acceleration with Sn inclusion, allowing attribution of decay components with core, mixed, and defect-related character. Further Arrhenius analysis reveals distinct thermally activated channels; a shallow confinement dependent pathway with EA1 ∼ 7−19 meV potentially corresponding to dark-bright excitonic state splitting alongside a deeper channel with EA2 ∼ 46−162 meV, likely associated with parasitic traps or surface states across the alloy series. These results provide groundwork for enhancement of the notoriously low emission efficiencies in Ge-based nanoemitters, contributing towards further understanding of dark states, defects, and their roles as key limiting mechanisms.