Photoluminescence Quenching Versus Enhancement of InP Core/Shell and Core/Shell/Shell Quantum Dots Induced by Adsorption of Rhodamine Dyes

ABSTRACT We compare the photoluminescence (PL) quenching of InP/ZnS core/shell (CS) and InP/ZnSe/ZnS core/shell/shell (CSS) quantum dots (QDs) in assemblies with Rhodamine dye molecules of different ionic characters, Rhodamine 560 (cationic) and Rhodamine 575 (zwitterionic). Steady‐state and time‐resolved optical spectroscopy data reveals that the Stern–Volmer (SV) constant K SV and bimolecular quenching rate constant k q are significantly higher for CSS QDs, which is attributed to the expansion of the conduction band (CB) electron wave function from the InP core to the outer ZnS shell, making electron transitions occur more likely to the dye‐induced surface states. Further, we show that the QD PL quenching can be controlled by varying the excitation wavelength; that is, quenching is less pronounced at longer excitation wavelengths (500 nm vs. 450 and 410 nm). Although longer excitation wavelengths lower the chance of excited charge carrier's interaction with surface traps or phonons and related nonradiative recombination, they excite dye molecules significantly and cause Förster resonance energy transfer (FRET) from dyes to QDs. Since the distance between QD and dye molecules is relatively small in assemblies with CS QDs compared to CSS QDs, an efficient FRET (77%) process can contribute to CS QD's PL enhancement in the assembly under 500 nm excitation, suggesting their suitability for bioimaging applications. However, for CSS QDs, the intermediate ZnSe shell lowers the FRET efficiency (18%). We estimate that the PL quenching rate exceeds the FRET rate by a factor up to 10.3, reflecting effective charge separation, making these assemblies promising for dye‐sensitized solar cells.