Surface modification of ZnO tetrapods using sodium sulfide and their two-photon luminescence properties

In this paper, the surfaces of ZnO tetrapods were modified by Na2S to form composite ZnS/ZnO hollow tetrapods for the first time. Two-photon luminescence spectra with the excitation having double longer wavelength than the emission indicated that two-photon absorption was involved in the excitation processes, and the photon luminescence enhancement of ZnS/ZnO hollow tetrapods more than that of ZnO tetrapods was ascribed to the capping of ZnS, which could passivate the surface traps of ZnO. The time-resolved PL decay traces showed that the lifetime of ZnO/ZnS hollow tetrapods was much longer than that of ZnO tetrapods due to the capping of ZnS on the surface of ZnO causing the reducing surface defects and then significant effect on its surface states.