Reducing Competition by Coordinating Solvent Promotes Morphological Control in Alternating Layer Growth of CdSe/CdS Core/Shell Quantum Dots

The formation of core/shell structures in colloidal semiconductor nanocrystals is important in maintaining the spectroscopic properties of colloidal quantum dots (QDs) and defining new functions. When using selective ionic layer adhesion and reaction (SILAR)-based techniques, conversion of shell precursors to surface-adsorbed equivalents should be maximized for effective control of shell growth. In this work, we monitored precursor conversion and shell growth on CdSe QDs in the presence of three different amine solvents in an effort to increase the synthetic yield of shell growth. UV–vis and photoluminescence spectroscopy are applied to monitor shell growth. Photoluminescence excitation spectroscopy was applied to confirm the presence/absence of precursor nucleation. Additionally, during shell growth, the free precursor concentration was measured by inductively coupled plasma mass spectrometry (ICP-MS), and fit with a Langmuir isotherm-based model, which reveals the influence of the different solvents on the fractional occupation of shell precursor equivalents on the QD surface. The binding affinities of the solvent molecules to the QD surface are also studied to understand the influence of such interactions on shell growth. We find that a tertiary amine solvent is effective in increasing precursor conversion and suppressing nucleation of side products when compared to primary and secondary amines at similar solvent mole fraction. The difference appears to be associated with competition for surface sites between the metal carboxylate precursor and the primary amine. This study is important for understanding the mechanism of growing the core/shell nanoparticles via SILAR technique and further could be applied to synthesize isotropic/anisotropic core/shell nanoparticles in an advanced and controllable manner.