Reduction of fluorescence resonance energy transfer by space control between quantum dots via direct bonding of reactive ligands to the polymer matrix for color conversion films

Fluorescence resonance energy transfer (FRET) between quantum dots (QDs) is one of main mechanisms that cause efficiency to drop in photoluminescence (PL) applications. In this work, we reduced FRET by controlling the distance between the QDs via chemical reactions between the QD ligands and long-chain linkers. The oleic acid ligands of the QDs were replaced with ligands containing reactive alcohol groups without any degradation in the quantum yield by a one-pot reaction. The alcohol groups of the QD ligands were reacted with polycaprolactone diol, which acted as a spacer, and tris(isocyanatohexyl)cyanurate to form cross-linked urethane bonds. The interconnected QD film showed 26% higher quantum efficiency and 19% longer PL decay time than that of a conventional film in which the QDs were randomly embedded in PMMA. The interconnection of the designed QD and the long spacer with the cross-linker is believed to prevent FRET between QDs and enhance the quantum yield of the QD films.