Efficient Addition of Desired Carboxylate Ligands to CdSe Quantum Dots Passivated with Phosphonic Acids

Phosphonic acids bind strongly to quantum dots (QDs), improving stability. However, it is difficult to introduce desired ligands to QDs passivated with phosphonic acids via ligand exchange. Here, we have investigated the efficient addition of X-type ligands to wurtzite CdSe QDs passivated with phosphonic acids using Z-type ligands. Oleic acid (OA) and Cd(OA)2 were used as examples of the desired X-type and Z-type ligands, respectively, and octadecylphosphonic acid (ODPA) was used as a passivating ligand for CdSe QDs. OA ligands were not introduced at all into the QDs when OA itself was used as the X-type ligand. However, after Z-type ligand addition, the added OA ligand accounted for 35% of the total ligands and only 20% of ODPA was dissociated from QDs. In addition, photoluminescence (PL) and its lifetime increased 6.1 and 2.8 times, respectively, indicating that Z-type ligands bound to trap sites to increase PL. Thus, we suggest that a sufficient amount of the desired ligand can be introduced, enhancing the quantum yields of CdSe QDs substantially. Our approach can be applied to various applications requiring energy input/output control and exciton lifetime extension in QDs.