Effect of Ligand Chain Length on Morphology and Optical Properties of Colloidal CdSe Quantum Dots

Colloidal CdSe quantum dots (QDs) are promising materials for optoelectronic and photonic applications because their optical properties can be controlled through size, morphology, and surface chemistry.In this study, we investigated the effect of carboxylic acid chain length on the morphology and optical properties of CdSe QDs by comparing oleic acid (OA), a long-chain ligand, with octanoic acid (OTAc), a short-chain ligand.Transmission electron microscopy revealed that OA promoted the formation of nearly spherical QDs, whereas OTAc induced anisotropic growth, producing tetrapod-like nanocrystals.Photoluminescence (PL) spectra showed that the emission peak of the OA system shifted from 530 to 605 nm with reaction time, whereas the OTAc system shifted more rapidly from 535 to 620 nm and exhibited broader emission linewidths.Time-resolved PL measurements further confirmed ligand-dependent recombination kinetics, with OTAc-derived tetrapods showing decreased decay times at longer wavelengths, suggesting enhanced nonradiative recombination associated with anisotropic morphology.Unlike previous studies mainly focused on size control, this work demonstrates that ligand chain length alone can switch the growth pathway from isotropic QDs to anisotropic tetrapod-like nanocrystals, enabling simultaneous control of morphology, emission evolution, and carrier recombination dynamics.