Assembly And Optoelectronic Properties Of Water-soluble CdTe QDs Thin Films

There are two parts in this thesis as follow:I Synthesis of water-soluble CdTe QDs and their thin films assemblyHigh luminescence CdTe QDs were synthesized in aqueous media using TGA and MPA as stabilizers. The change of the emitting properties during the growth and the effect of ligand on the particle size of CdTe QDs were investigated systemically. Experimental results found that the linewidth of CdTe QDs first narrowed followed by broaden, the photoluminescence intensity first enhancing then decreasing. In the same experimental conditions, when using MPA as a stabilizer, the CdTe QDs were easily larger particle sizes and exhibited longer emitting wavelength. Afterward, CdTe QDs emitting at different wavelength were used to assemble on an ITO electrode by layer-by-layer assembly. The coloration of number of layers and photoluminescence intensity was studied. It was found that the absorbance and PL intensity of thin film rose as the increase of the layers of CdTe QDs. There was no significant variation of the dispersibility and size distribution of QDs assembled on the ITO glass, as compared with the CdTe QDs solution. The thin films of CdTe QDs by LBL assembly was not absolutely even, as characterized by AFM, however, the fluctuation was within the acceptance.II FRET between LBL CdTe QDs thin films of different emitting wavelengths In the present study, we observed clear fluorescence resonance energy transfer (FRET) between certain different emitting wavelength CdTe QDs when assembly on the same piece of ITO glass. Typically, when difference layers of560nm CdTe NCs were assembled on the640nm CdTe thin layers, there was a clear coloration of efficiency of FRET and the number of layers. In this system,560nm CdTe QDs acted as a donor of energy transfer while640nm CdTe QDs acted as an acceptor. However, the opposite assembly sequence, that is, assembly of640nm CdTe QDs on the560nm ones did not lead to obvious FRET. The origin of such FRET was studied by the absorption and emission spectra of thin layer consisted of these two QDs, and the favorable pathway of FRET was also investigated. The variation of fluorescence lifetime of these two QDs in thin layers were further measured before and after FRET happened, and the possible mechanism and efficiency of FRET was further elucidated. It was found that the emitting efficiency of acceptors was enhanced markedly by FRET of CdTe QDs thin layers. The photoelectric response of LED device constructed by CdTe QDs LBL assembly was measured during the experiments.