This paper describes the mechanism behind the pH response of the photoluminescence (PL) of aqueous dihydrolipoic acid (DHLA)-capped PbS quantum dots (QDs). The PL spectra of ensembles of PbS-DHLA QDs bathochromically shift by up to 95 meV as the pH value decreases from 12 to 5. The results of optical spectroscopy and dynamic light scattering experiments, along with the results of a phenomenological model for exciton hopping among QDs, suggest that bathochromic shifts can be entirely accounted for by Förster-type energy transfer (EnT) among QDs as they aggregate with decreasing pH. The magnitude of the PL shift is strongly correlated with the full width at half maximum (fwhm) of the ensemble's PL in its most disaggregated state (i.e., the polydispersity of the sample directly after phase transfer into basic water). Extrapolation of these data to a hypothetically completely monodisperse sample of QDs yields a PL fwhm of an ensemble of single DHLA-capped PbS QDs in water of 130 meV. This work shows that the PL linewidth before aggregation, which is controlled by the phase transfer procedure, is an excellent predictor of the pH response of the emission spectra of the QDs.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films