Preparation And Luminescence Properties Of Doped ZnS Nanoparticle Clusters With Different Core/Shell Structures

As an important type of semiconductor luminescent material, doped ZnS nanoparticles with many excellent optical and electrical properties has a promising application prospect in light-emitting diodes (LEDs), flat panel displays, near infrared windows, sensors, lasers and biological fluorescence labels. However, a large portion of atoms are usually located on or near the surface of nanoparticles (NPs). The surface states usually act as luminescence quenching centers and result in low luminescence efficiency. The surface modification (modifier capping or core/shell structure) can improve efficienly the luminescent properties of NPs. This thesis describes the preparation and optical properties of ZnS and doped ZnS NPs with different modifiers, and ZnS:Mn (or Cu) nanoparticle clusters with different core/shell structures. The main research results are as follows:(1) Almost monodispersed ZnS, ZnS:Cu and ZnS:Mn NPs were prepared in ethanol medium when the octadecyl amine (ODA) was used as modifier. A blue emission band centered at423nm of ZnS NPs could be attributed to the transition from the shallow donor level to the deep shallow acceptor level caused by Zn vacancies. A green emission band of ZnS:Cu NPs indicated that Cu2+were indeed incorporated into the host ZnS nanocrystal. For ZnS:Mn NPs, only the blue emission corresponding to ZnS nanoparticles was observed.(2) When the polyvinylpyrrolidone (PVP), cetyltrimethyl ammonium bromide (CTAB), sodium tripolyphosphate (STPP),3-mercapto propionic acid (MPA) or thioglycolic acid (TGA) was used as modifier, only the nanoparticle cluster could be formed by aggregation of NP units. The blue emission band of those nanoparticle clusters could be attributed to defects in ZnS (S or Zn vacancies).(3) The Mn2+doped ZnS nanoparticle clusters with different core/shell structure were prepared by a chemical co-precipitation method:①ZnS:Mn without shell layers;②ZnS/ZnS:Mn;③ZnS:Mn/ZnS. The nanoparticle clusters with ZnS/ZnS:Mn core/shell structure confined the sensitizers (ZnS) and the activators (Mn2+) to the cores and the shells, respectively, and therefore enabled the migrators (sulfur vacancies) to transfer energy within an appropriate average route length, thus producing the highest energy transfer efficiency and the most intense orange emission of Mn2+in the nanoparticle clusters with ZnS/ZnS:Mn core/shell structure. (4) The ZnS:Cuu、ZnS:Cu/ZnS and ZnS/ZnS:Cu nanoparticle clusters were prepared by a chemical co-precipitation method. For ZnS:Cu nanoparticle clusters, the emission band shifted to lower energy with the increase of Cu2+concentration. For ZnS:Cu/ZnS nanoparticle clusters, the emission band shifted to lower energy slowly with the increase of Cu2+concentration. For ZnS/ZnS:Cu nanoparticle clusters, emission band was broaded and shifted to the green band with the increasing of Cu2+concentration.