Variations in Photoluminescence Intensity of a Quantum Dot Assembly Investigated by Its Adsorption on Cubic Metal–Organic Frameworks

Abstract

In this study, a novel method is proposed for investigating energy transfer between quantum dots (QDs), especially of the same type, in an ensemble by employing cubic crystals of a commonly used metal–organic framework-5 (MOF-5). Three types of QDs were synthesized by standard methods and ligand-exchanged with weakly bound pyridine derivatives; thereafter, they were instantaneously adsorbed on MOF-5 in a monolayer by simply mixing both the materials. When two types of QDs were simultaneously loaded, energy transfer from the green- to red-emitting QDs as reflected by an increase in the photoluminescence (PL) intensity of the long-wavelength component was clearly observed. Conversely, when the same type of QDs were loaded on MOF-5, the increase in the PL intensity was lower than that expected corresponding to the amount of QDs and the deviation between the expected and measured values was different based on the type of QDs. These behaviors are discussed in relation to the occurrence of the Förster resonance energy transfer between the same species in close distance and the existence of temporarily or permanently dark QDs.