Publication date: 15th May 2025
Photoluminescence-spectroelectrochemistry (PL-SEC) is used to study charge carrier relaxation processes in semiconductor nanostructures.[1,2] PL-SEC allows us to reversibly block charge carrier relaxation pathways by electrochemically filling or emptying the involved states. Here, we focus on changes in the PL signal of CdSe/CdS dot-in-a-rod (DRs) nanostructures as a result of electrochemical electron injection into surface trap states and conduction band states.
CdSe/CdS DRs with trioctylphosphine oxide (TOPO) ligands as well as sulfide ligands were studied. Changing the ligands varies the type and density of trap states on the surface of the particles. This drastically influences the PL-SEC response. PL quenching upon electron injection was observed for high quantum yield (QY) particles capped with TOPO-ligands, whereas PL enhancement was observed for sulfide-capped low QY particles. These measurements indicate fast electron trapping on surface sulfur species and subsequent non-radiative recombination in sulfide-capped DRs. Furthermore, the non-radiative recombination centers could be passivated chemically by treatment with cadmium salts, which resulted in an enhanced QY and a recovery of the PL-SEC response that was obtained prior to ligand exchange.
This study shows the impact of surface chemistry on semiconductor nanocrystal PL-SEC measurements. Furthermore, it aims to lay a foundation for studying charge transfer processes in more complex systems such as metal-tipped semiconductor nanocrystals with potential application in photocatalysis.
[1] Ashokan et al., Chem. Mater. 2024, 36, 1810-1817. [2] W. van der Stam et al., Chem. Mater. 2018, 30, 8052−8061.
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