Colloidal Synthesis And Electroluminescence Properties Of Zinc-based Core/shell Nanoparticles

Zinc-based quantum dots （QDs） materials have received extensive attention because oftheir wide band gap, environment-friendly and simple preparation processes. In theapplications of electroluminescence （EL） devices, semiconductor nanoparticles can be actedas active layer or functional layer. For example, intrinsic defect emission of QDs could beused to achieve different colors of light. However, the shortcoming of nanoparticles-based ELis that the emission of dopant was quite difficult to be obtained because the energycompetition from intrinsic defect or surface defect states. Core/shell structure are regarded aseffective way to improve luminescent properites. And the wider bandgap of shell than that ofcore materials is a way to restrict carries in the core and to control the carrier transport process.In this thesis, we foucus on the EL properties and the carrier transport mechanisms ofcore/shell ZnS and ZnO QDs. The main experiments and discussions are as follows:1) The devices based on ZnS:Mn/SiO₂QDs with different silica concentration wereformed via spin-coating technique. In the difference with the device using uncoated ZnS:MnQDs, in which the emission of intrinsic defect is dominant, the EL spectrum with silica on theQDs showed obviously the emission of Mn2+ions. The width of SiO₂layer on enhancementof Mn intensity was acquired and was owed to carrier confinement effect of silica. The hybridEL device having a organic/inorganic multilayer structure of ITO// PVK: TPD //ZnS:Mn/SiO₂QDs //Al was fabricated and white light emission was obtained.2) A EL device with structure of ITO//ZnS/SiO₂QDs: PVP//Al was fabricated by spincoating from the mixing solution of ZnS/SiO₂QDs and PVP. The EL emission peaks, whichare associated with defects in ZnS QD, were observed shifting from 560nm to 510nm with anadditional shoulder at 400 nm with the forward bias applied voltage increase. The high barrieron the surface of ZnS formed by amorphous silica and high-level steps of PVP has commonlyimproved the luminous efficiency in the high-energy region. With the emission increase in theshort wavelengths （violet light）, the chromaticity coordinates approached to white light.3) Hybrid organic/inorganic devices were fabricated with ZnO/SiO₂QDs as hole bufferlayer. By comparison with device without QDs layer, the balance of carrier injection wassignificantly improved by the QDs layer and the EL intensity of the organic material wasincreased. By investigating devices with different sizes of the QDs, it was observed thatsmall-size QDs with a certain thickness of the silica would improve the EL intensity andluminous efficiency of the device.