Surfactant-Mediated Doubling of Förster Resonance Energy Transfer in Quinolate-Complexed CdS Quantum Dots

Colloidal CdS quantum dots (QDs) are promising FRET donors, yet surface traps severely limit their photophysical performance. Herein, we demonstrate that cetyltrimethylammonium bromide (CTAB) acts as an efficient interfacial modifier that reduces the donor–acceptor separation distance and enhances Förster resonance energy transfer (FRET) in CdQ 2 -attached CdS quantum dot (QD)–Rhodamine B (RhB) assemblies. CTAB modification preserves the crystal structure and morphology of CdQ 2 -attached CdS QDs while passivating surface trap states, leading to improved photoluminescence and extended exciton lifetimes. Zeta potential and FTIR analyses confirm charge inversion and dual-mode interactions, where CTAB electrostatically anchors to CdQ 2 -attached CdS QDs and hydrophobically associates with RhB, reducing donor–acceptor separation. Consequently, CTAB-modified systems exhibit nearly 2-fold enhancement in FRET efficiency (71.28 ± 3.35% vs 35.85 ± 2.21%), supported by steady-state quenching and time-resolved decay studies. Control experiments exclude artifacts from pH, dilution, and direct sensitization effects. This work establishes surfactant-mediated interfacial engineering as a powerful strategy to modulate nanoscale energy transfer in semiconductor QD systems.