Preparation And Characterization Of Zinc Oxide Quantum Dots

Quantum dots (QDs), as a new class of luminescent materials, have shown potential applications in biological fluorescent labels for their broad excitation spectrum, narrow emission spectrum and long lifetime. Synthesis and application of QDs have generated a tremendous amount of interests in the fields of bio-chemistry. Besides, doped quantum dots have caught the attention of many researchers for their unique luminescent properties. But it’s extremely important to avoid the aggregation and fluorescence quenching of QDs during the process of impurity ions diffusing into the intrinsic lattice of the QDs. In view of these, a series of work and some innovative results have been achieved:1、Core-shell structured ZnO@Cd(OH)2nanoparticles with stable and improved luminescence have been successfully prepared via a facile ultrasonication-assisted sol-gel method. Their composition and structure have been confirmed by XRD, EDX, XPS and FT-IR spectra. The size of the nanoparticles decreases gradually along with the increase of the shell thickness, indicating that Cd(OH)2shells can hider ZnO cores growth and aggregation effectively. These core-shell nanoparticles can be stored at room temperature for several weeks without luminescence efficiency reduction, and they are quite stable at elevated temperatures or in moderate alkaline solutions due to the protection of the Cd(OH)2shell.2、Red-emitting Eu3+-doped ZnO QDs with effective energy transfer were successfully prepared via two steps of nucleation doping and lattice diffusion. Under the protection of SiO2matrix, the aggregation and growth of QDs were greatly inhibited, and the Eu3+ions on the grain surface were restricted for movement and then diffused into the space lattice of ZnO during the heat treatment process. The HRTEM images showed the uniformity of the particle size, while the Eu doping could be proved by TEM, SAED, EDX, XPS, PL measurements. From the PL spectra and the decay times, the energy transfer between host ZnO and Eu3+was discussed as well as the efficiency. Based on all the test results, a reasonable mechanism was put forward to illustrate the fluorescence emission and the energy transfer.