Optical Properties of ZnO Quantum Dots in Epoxy with Controlled Dispersion

Optical properties of monodisperse colloidal ZnO quantum dots (QDs) having various degrees of dispersion in epoxy have been systematically studied. Exfoliated cc-zirconium phosphate (ZrP) nanoplatelets, instead of organic capping agents, were utilized to control the state of dispersion of ZnO QDs. High resolution transmission electron microscopic images confirm that, without the presence of ZrP, ZnO QDs form large aggregates in epoxy but become well dispersed with the aid of exfoliated nanoplatelets. The epoxy hybrid nanocomposites containing well dispersed ZnO QDs and exfoliated ZrP nanoplatelets show transparency similar to that of the neat epoxy and exhibit high UV-absorption efficiency. The epoxy hybrid nanocomposites also give off sharp UV emission upon excitation. The optical absorption and photoluminescence of well dispersed ZnO QDs in epoxy exhibit a red-shift as the QD concentration is increased due to the QD coupling effect. This finding demonstrates that the optical properties of polymer/QD nanocomposites can be tuned by adjusting the dispersion state of QDs in polymers. The present study is also significant for better understanding of the optical properties of semiconductor nanocrystals in polymers and would help in the design of organic/inorganic hybrids for optical, electrical, and photovoltaic applications.