Reversible phase transfer of luminescent ZnO quantum dots between polar and nonpolar media

A facile and reversible phase-transfer protocol for luminescent ZnO quantum dots (QDs) between methanol and hexane is presented. Oleylamine together with acetic acid trigger this reversible phase-transfer process, during which the structure and optical properties of the ZnO QDs are well-protected. ZnO QDs with a diameter of approximately 5 nm emit yellow light at 525 nm, while those with a diameter of approximately 4 nm emit green light at 510 nm. The positions of the emission peaks remain unchanged during the presented phase-transfer process. The Pearson's hard and soft (Lewis) acid and base principle, together with the principle that similar substances are more likely to be dissolved by each other, describes the current reversible phase-transfer process. Herein, we circumvent the time-consuming work required to synthesize ZnO QDs in different environments, making it possible to combine the advantages of ZnO QDs dispersed in polar and nonpolar solvents.