Low-Energy Cathodoluminescence of Type-I CdSe/ZnCdS Quantum Dots

Quantum dots (QDs) are a cornerstone of modern nanotechnology due to their unique optical properties. In this study, we investigate excitation dynamics in II–VI core–shell QDs under high carrier injection conditions using low-energy cathodoluminescence (CL) in a scanning tunnelling microscope (STM) setup. This approach enables spatially confined excitation of a limited number of QDs and access to higher-order excitonic states. We find that electron energies of at least 130 eV are required to induce luminescence, with no emission observed below this threshold. In QDs with thin shells (1.2 nm), increasing excitation energy modifies both luminescence intensity and spectral features, indicating altered carrier distributions and multiexciton processes in the core. In contrast, QDs with thicker shells (4.2 nm) exhibit predominantly single-exciton emission under the same conditions, consistent with reduced electron reach and carrier generation in the core. The results are compared with low-power continuous-wave photoluminescence (cw-PL), revealing distinct excitation pathways and charge dynamics. Prolonged electron exposure leads to a significant decrease in CL intensity without spectral shift or broadening, suggesting blinking behavior likely caused by charging of the QD shell. These findings provide new insight into energy deposition, carrier recombination, and beam-induced effects in core–shell QDs under localized excitation conditions.