Preparation And Characteristics Of The Rare-Eearth Doped ZnS Quantum Dots

Nanoscience has been drawn considerable interest and physicaly investigated all over the world. The nanoparticles have different properties compared with bulk materials such as quantum size effect, surface effect and the dieletric confinement. As one part of nanotechnology, semiconductor quantum dot structures are of great importance not only in basic physical problems but also in practical applications. Therefore, the research on quantum(sQDs)is very significant both in academic and application. The optical properties of quantum dots doped with activator elements led to a new stage of investigation of optical characteristics of nanoparticles. In this thesis, we deal mainly with the preparation and characterization of the rare-earth doped ZnS QDs. The major results are listed below:1. ZnS QDs with different Eu ³⁺ doping concentration were synthesized in aqueous solution. Photoluminescence emission spectra show that there are two narrow and symmetrical emission peaks at 614nm and 591nm respectively and the ratio of intensity of these two emissions will increase with the increase of Eu³⁺. This phenomenon reveals that the distribution of probability of Eu³⁺ in different symmetrical center of ZnS lattice is affected by the concentration of Eu³⁺ and the site symmetry of Eu ³⁺ reduces as the increasing of Eu³⁺.ZnS:Eu QDs'stability of fluorescent intensity was also discussed in this article.2. ZnS:Eu QDs'fluorescent characteristic is improved by adding the charge composition ions with various valences, coating a shell of ZnS and preparing ZnS:Eu QDs by microemulsion method. The results indicate that the as-prepared QDs by these methods have higher photoluminescence efficiency.3. ZnS:Tb and ZnS:Er QDs were synthesized at room temperature by aqueous precipitation. Under the excitation of a 810nm near infrared luminescence, upconversion luminescence of Er³⁺ were observed. They locate at 464nm,537nm and 576nm, conresponding to ⁴I_15/2→⁴ F_5/2,⁴I_15/2→²H_11/2,⁴I_15/2→⁴S_3/2 transitions of Er ³⁺ respectively.4. Porous aluminum oxide nanoparticle was prepared by the method of spray drying. Using the aluminum oxide nanoparticle as the template, the"host-guest"of nanoscale Eu₂O₃/Al₂O₃ are adapted to wetness impregnation technique. From PLE spectrum, we could find there are two bands for templeted Eu₂O₃/Al₂O₃ samples, the wide one is associated with charge transfer (CT) transition from 2p orbital of O₂^- ions to the 4f orbital of Eu³⁺ ions, and the sharp lines correspond to direct excitation of f-f shell transitions.