We next examine the optical properties of the grown ZnO nanostructures as shown in Fig. 3. The UV emission at 381 nm is the near band edge (NBE) emission, and the green luminescence belongs to the defect emission of zinc oxide [13]. For the sample grown without inclusion of In, the intensity of NBE emission is stronger than that of defect emission, and the ratio of the intensity is about 9:1. After the incorporation of In in the growth process, the NBE emission is enhanced, while the defect emission is suppressed, and the ratio of the intensity of the peaks changes to 200:1. Generally speaking, it is unusual that doping can enhance NBE emission and suppress the defect emission [11]. Since it is expected that doping adds impurities to the crystal, the defect luminescence will be enhanced. Besides, with excess acceptor or donor levels, they will trap photoexcited electron-hole pairs, and reduce the NBE emission. In addition to the XRD data, our result presented here indicates that the inclusion of In in the growth process does not lead to a significant amount of the incorporation of In inside the ZnO crystals. Furthermore, the fact that the CL peak remains the same for both kinds of samples also provides another supporting evidence. The major effect of In inclusion in the growth process is therefore not to incorporate In elements inside the ZnO crystal lattice, but only to decrease the growth rate, improve the crystalline quality, and reduce defect concentration.