FRET between Close-Packed Quasi-Monodispersed PbS QDs in a Porous Matrix

Forster resonant energy transfer (FRET) between PbS quantum dots (QDs) in assemblies of QDs with a narrow size distribution (quasi-monodispersed), embedded in a porous matrix, is investigated. Analysis of size-selective steady-state and transient photoluminescence (PL) of these assemblies demonstrates the influence of FRET on the QD optical properties. In particular, we found that FRET drastically changes the QD PL lifetime size-dependence. We show that the FRET efficiency increases up to 35% as the QD concentration in the matrix increases. The observed saturation of the energy transfer efficiency is attributed to the formation of ordered, close-packed, QD structures with minimal interdot distance and, therefore, maximal FRET efficiency. Evidence supporting this conclusion is supplied by small-angle X-ray scattering (SAXS) measurements. Thus, we demonstrate that FRET analysis supplies information regarding the formation of a close-packed ordered structure.