Amine-Mediated Diameter Control of Core/Shell Nanorods for Tunable Band Structure and Enhanced Optical Anisotropy

Semiconductor core/shell nanorods (NRs) exhibit highly diameter-dependent optical properties. However, post-synthetic strategies for broad and controllable diameter modulation remain limited. Here, we present an amine-mediated approach that enables wide-range diameter modulation of CdSe/CdS NRs through two distinct, temperature-dependent pathways: intraparticle ripening and etching. These opposing processes allow continuous expansion or reduction of NR diameter, leading to systematic red- and blue-shifts in photoluminescence along with corresponding changes in band alignment and exciton dynamics. Notably, diameter reduction via etching induces a pronounced enhancement of fluorescence anisotropy. Continued etching beyond shell thinning leads to anisotropic reshaping of the CdSe core into a more elongated geometry, which enhances light-hole-heavy-hole subband splitting and results in strongly linearly polarized emission. These results suggest that, although smaller cores are typically associated with reduced fluorescence anisotropy, diameter reduction coupled with anisotropic core reshaping provides a viable strategy to enhance anisotropy. At the ensemble level, this enhancement leads to high polarization contrast after macroscopic alignment. This work establishes amine-mediated diameter engineering as a versatile post-synthetic approach for simultaneously tuning excitonic structure and fluorescence anisotropy of semiconductor NRs, providing a practical design guideline for polarized light-emitting and optoelectronic applications.