| Nanomaterials have unique properties associated with its surface effects, volume effects and quantum size effects, making it a center of research interests both in fundamental science and applied research. On the other hand, doping is an important material modification technology for electro-optical and semiconductor materials to achieve desirable properties. How to prepare nanomaterials with a controlled doping level to achieve tunable properties is an important research subject.Zinc oxide is an important wide band gap semiconductor material. Zinc oxide nanomaterials possess excellent properties of both nanomaterials and semiconductor materials, showing great potential in many applications including field-emission displays, solar cells, diodes, sensors and UV light-emitting devices. As one of the chemical methods to prepare zinc oxide nanomaterials, the hydrothermal method has been used widely in research laboratories because it is inexpensive, easy to operate and has various experiment paths to realize controllable particle shape and size.In this dissertation, ZnO and doped ZnO nanocrystals with different microstructures and morphologies were synthesized by hydrothermal and high-temperature nitriding techniques. The phase compositions and microstructures of the ZnO nanocrystals were investigated by X-ray diffraction(XRD), X-ray energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM), field emission scanning electron microscopy (FESEM) and selected area electron diffration(SAED). The reaction process and growth mechanism of the ZnO nanocrystals were discussed based on available experiment data. The spectra characteristics and the optical properties of ZnO nanocrystals were analyzed by fourier transform infrared spectroscopy(FTIR), UV-visible spectroscopy(UV-vis) and photoluminescence spectroscopy(PL). The main contents of this dissertation are summarized as follows:Using zinc acetate dihydrate as the source of zinc, ZnO nanorods with an uniform size distribution were prepared at 200℃via a H2O2-assisted hydrothermal process. From the HRTEM and SAED results, these nanorods were found to be single crystalline and have a wurtzite crystal structure. These nanorods have a hexagonal cross section with a diameter in the range of 120～300 nm and grow along the [0001] crystallographic direction with an average length of 1～2μm. On the other hand, the ZnO rods prepared by the regular hydrothermal process showed a much larger diameter in the range of 1～5μum and a length of 5～20μm. Furthermore, the ZnO nanorods prepared by the H2O2-assisted hydrothermal process showed an increased UV emission intensity at the wavelength of 390nm from the room temperature PL results, as compared with that of the regular hydrothermal ZnO product. It is concluded that the addition of H2O2 can facilitate the nucleation process and slow down the growth rate of ZnO crystal, hence improving the crystalline quality. A possible growth mechanism for these nanorods was proposed based on experiment data.By applying H2O2-assisted hydrothermal process to low temperature (80℃) synthesis of ZnO using zinc nitrate hexahydrate as the source of zinc, smaller ZnO nanorods were prepared. By selecting an appropriate amount of H2O2 in the hydrothermal process, the resulting ZnO nanorods can have a strong ultraviolet emission peak and a much reduced defect emission peak.Using ZnCl2 as the source of zinc and SnCl4·5H2O the source of Sn, Sn-doped ZnO nanocrystals were synthesized by the regular hydrothermal method. The as-grown Sn-doped ZnO nanocrystals have a hexagonal wurtzite crystal structure. With the increase of Sn concentration, the average grain size of the nanocrystals increases and their morphology changes from short rod-like to single cone-like and double cone-like. In addition, the morphology of the nanocrystals can also be engineered by tuning the pH value of the precursor solution. For example, the nanocrystals changed from long nanorods to short nanorods when the pH value increased from 7.0 to 12.0. In the room temperature PL spectra of these nanocrystals, three emission bands, including a strong purple band peaked at 433nm, a left-shoulder near UV band peaked at 401nm as well as a weak blue band peaked at 466nm were observed. It was found that the peak positions are independent of the Sn concentration. In the UV-vis spectra for the ZnO nanocrystals, there was a UV absorption peak, which showed a red-shift with the increase of Sn concentration.N-doped ZnO(NZO) nanocrystals were synthesized by annealing double cone-like ZnO nanocrystals prepared by a hydrothermal method in an ammonia atmosphere. The resulting NZO nanocrystals have a hexagonal wurtzite structure with a double cone-like morphology. From the XRD analysis, NZO nanocrystals prepared by such a high-temperature nitriding process showed better crystallinity and larger crystal size, as compared with undoped ZnO nanocrystals. Room temperature PL spectra showed that the NZO nanocrystals have a strong UV emission peak at 389nm and a weak blue emission peak at 468nm. However, the green emission peak at 554nm observed in the PL spectrum of the undoped ZnO disappeared in the PL spectrum of ANZO. It was proposed that the absence of the green emission peak in N-doped ZnO nanocrystals may be due to the decrease of oxygen vacancies, which can be compensated by the incorporation of N.Al, N co-doped ZnO(ANZO) nanorods were prepared by annealing Al doped ZnO (AZO) nanorods prepared by regular hydrothermal method at 550℃in an ammonia atmosphere. The results showed that the as-grown AZO and ANZO nanorods are all single crystals with a hexagonal wurtzite structure. It was found that the diameters of the ZnO rods decrease significantly by the addition of Al. For example, the microrods (average diameter～3μm) of undoped ZnO changes into nanorods (average diameter～70 nm) by the addition of 1% Al. From the EDS results, it was confirmed that Al and N elements were successfully incorporated into the ZnO nanorods, and the content of N increases with Al concentration. Room temperature PL spectra showed that both AZO and ANZO nanorods have a strong UV emission peak at 390nm and a weak blue emission peak at 468nm. However, the green emission peak at 555nm observed in the PL spectrum of AZO disappeared in the PL spectrum of ANZO.
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