Study On Synthesis And Photoluminescence Properties Of Ⅱ-ⅥSemiconductor Nanomaterials

Zinc sulfide (ZnS) and zinc oxide (ZnO), well-known direct bandgap II-VI semiconductors, are widely used in photonic, optical, and electronic devices. They have attracted particular attention in recent years owing their exceptional optical, electrical and chemical properties. In this thesis, zinc sulfide semiconductor nanocrystals doped with rare earth ions have been prepared through a sol-gel method using PVP (polyvinylpyrrolidone) as a capping agent. Photoluminescence spectra were recorded for zinc sulfide semiconductor nanocrystals doped with rare earth ions at different temperatures. The ZnO and ZnCdO microrods have also been prepared through a chemical bath deposition method. Photoluminescence spectra were recorded for ZnO and ZnCdO microrods at different excitation powers. The optical properties of semiconductive nanomaterials have been explored systematically. In addition, the whispering gallery modes (WGMs) of the ZnO photoluminescence emission were investigated in this thesis. The WGMs for two different polarizations will also be discussed in more depth.(1) The sol-gel method has been used for the synthesis of ZnS:Yb and ZnS:Er nanocrystals. The crystal structure and magnetic properties of the nanoparticles were investigated by X-ray diffraction (XRD) and Quantum Design physical properties measurement system (PPMS-9), respectively. Photoluminescence spectra the Yb3+-doped ZnS nanocrystals were recorded for doped ZnS nanoparticles at different temperatures. The results suggest that two emission bands have been observed at different temperatures. The peak of1.269eV is the transition from the lowest sub-level of excited state2F5/2to the lowest sub-level of ground state2F7/2. As the temperature increases, the bandwidth of1.269eV peak becomes larger. Its neighboring peak is likely to be a phonon replica. The shift of lower energy emission band has also been observed with the change of temperature. In addition, the samples of ZnS:Yb and ZnS:Er nanocrystals exhibit paramagnetic behavior at different temperatures. The magnetization of the ZnS:Yb and ZnS:Er nanocrystals increases with the increase of external magnetic field. The magnetic susceptibility is increased as the temperature is lowered.(2) Microrods of ZnO and ZnCdO were synthesized using a chemical bath deposition method. The structure and morphology of microrods were characterized using X-ray diffraction and transmission electron microscopy. Photoluminescence spectra were recorded for ZnO and ZnCdO microrods at different excitation powers. The intensity of UV emission is enhanced with increasing excitation power. The width of UV emission increases for spectra at higher excitation powers. The shift of UV emission band has been observed with the change of excitation power. In particular, the result shows that the influence of excitation power on the shift of emission band for ZnCdO microrods is more remarkable than that of ZnO microrods with the increase of excitation power.(3) Microrods of ZnO were synthesized using a chemical bath deposition method. The whispering gallery modes of the ZnO photoluminescence emission were investigated. The transmission electron microscopy and X-ray diffraction results show that the rectangle microrod has a single crystalline wurtzite structure. Except for the band-edge emission, the photoluminescence of the ZnO microrod presents the WGMs with two different polarizations. In a large waveband, the WGMs modes with two different polarizations have the same mode spacing. Due to the property difference, the WGMs for two polarizations have different appearances.