Ligand and solvent effects on the absorption spectra of CdS magic-sized clusters

The absorption spectra of congenetic wurtzite (WZ) and zincblende (ZB) CdS magic-sized clusters are investigated. We demonstrate that the exciton peak positions can be tuned by up to 500 meV by varying the strong coupling between X-type ligands and the semiconductor cores, while the addition of L-type ligands primarily affects cluster midgap states. When Z-type ligands are displaced by L-type ligands, red shifts in the absorption spectra are observed, despite the fact there is a small decrease in cluster size. Density functional theory calculations are used to explain these findings and they reveal the importance of Cd and S dangling bonds on the midgap states during the Z- to L-type ligand exchange process. Overall, ZB CdS clusters show higher chemical stability than WZ clusters but their optical properties exhibit greater sensitivity to the solvent. Conversely, WZ CdS clusters are not stable in a Lewis base-rich environment, resulting in various changes in their spectra. Our findings enable researchers to select capping ligands that modulate the optical properties of semiconductor clusters while maintaining precise control over their solvent interactions.

Automated summary

The absorption spectra of congenetic WZ and ZB CdS magic-sized clusters are studied. Exciton peak positions can be tuned by varying the coupling between X-type ligands and semiconductor cores, while midgap states are affected by L-type ligands. Red shifts in absorption spectra are observed when Z-type ligands are replaced by L-type ligands, despite a small decrease in cluster size. Density functional theory calculations explain these findings and highlight the importance of Cd and S dangling bonds during ligand exchange. ZB CdS clusters are more chemically stable but show greater sensitivity to solvents, while WZ CdS clusters exhibit various spectral changes in a Lewis base-rich environment. These findings enable researchers to selectively modulate the optical properties of semiconductor clusters while controlling their solvent interactions.