As a third-generation semiconductor material, ZnO has attracted extensive attention because of its excellent mechanical, thermal, optical and electrical properties, ease of preparation and environmental friendliness. In particular, high exciton binding (~60 meV) enables ZnO to exhibit unique advantages in the field of room temperature ultraviolet (UV) optoelectronic devices，and also provides an ideal carrier for the study of exciton-related light and matter interactions. The photoluminescence spectra of ZnO with different micro-/nano-structures have been widely reported, and have become an important means to reveal the radiation mechanism of ZnO. However, there are still ambiguous luminescence mechanisms and inadequate regulate and control means both for linear and nonlinear radiation processes of ZnO. Therefore, in-depth study and exploration of the linear and nonlinear optical processes of ZnO are of great value for its wide application in room temperature UV optoelectronic devices. In this thesis, the linear and non-linear photoluminescence spectra of different ZnO micro-/nano-structures were measured and compared, and the effects of excitation wavelength, intensity, temperature, applied voltage and other factors were investigated. The main research contents are as follows:

1.     Under 325 nm CW laser excitation, a series of fine spectral structures were observed in the low-energy side of the near band-edge (NBE) emission and the deep-level (DL) emission regions of the ZnO microbelt PL spectra at room temperature. The F-P cavity model was established by studying the influence of temperature and excitation power on the PL spectra and combining with the analysis of the mode spacing. Different from the DL emission region, the modes in the NBE emission region exhibited slight blue shift of the peak position and a superlinear increase of emission intensity with increasing the excitation intensity. These special radiation phenomena of the NBE emission region were explained in the exciton–polariton view. In addition, by applying voltage across the ZnO microbelt, a significant red shift of the resonance modes in the NBE region was observed, proving that the applied voltage could effectively regulate the cavity- polaritons.

2.     Under the excitation of femtosecond laser, the excitation wavelength dependence of the nonlinear spectra of ZnO microbelt was studied. The nonlinear spectra obtained under femtosecond laser excitation at different wavelengths could be divided into three regions: NBE emission dominated region, second harmonic generation (SHG) and NBE emission strong coupling region, and SHG dominated region. In the strongly coupled region, the nonlinear spectra contained three types of radiation: SHG, NBE emission, and DL emission. There was strong coupling and competition among the three, especially between SHG and NBE. A series of cavity modes existed in both NBE and DL emission region in the nonlinear spectra due to the microcavity effect of ZnO microbelt. On this basis, we demonstrated the competition and coupling between SHG and cavity modes in the NBE region at different excitation wavelengths and polarization configurations, where the intensity ratio could vary dramatically.

3.     The effect of applied voltage on nonlinear spectra of ZnO microstructures was studied. In view of the fact that the applied voltage could regulate the NBE emission behavior in nonlinear spectra, combined with the resonance and coupling between SHG and NBE, the effective regulation of SHG by applying voltage was achieved in a wide excitation wavelength range.