In the Zn1−x Cu x O nanostructures, the presence of the E2(high) mode confirms that they all have a typical hexagonal wurtzite structure, which is consistent with the above HRTEM and XRD observations. When the Cu content is 7%, the E2(high) and E1(LO) modes become broader and shift to lower frequency, as compared with the undoped counterpart. This may be due to the decrease in the binding energies of Zn-O bonds as a result of the Cu

doping, indicating that the long-range order of the ZnO crystal is destroyed S63845 datasheet by Cu dopants [32]. Figure 5 Raman spectra. Raman spectra of undoped ZnO and Zn1−x Cu x O samples with the Cu contents of 7%, 18%, and 33%. On the other hand, three additional modes at around 290, 340, and 628 cm−1 can be observed. They are attributed to the Ag, B1 g, and B2 g modes of CuO due to the vibrations of oxygen atoms, respectively [33, 34]. From Figure 5, it is obvious that the intensity of the CuO peaks enhanced while that of ZnO

peaks decreases with the Cu concentration increases up to 33%. Such behavior is caused by the competition of Zn and Cu during the oxidization process. In the sample with the highest Cu content of 33%, the formation of CuO is dominant, in spite of the fact that the lower melting point and higher vapor pressure of Zn than those of Cu under the same conditions [35]. The formation of CuO is significant to induce the usual ZnO hexagonal structures changing into four-folded find more cross-like structures, in good agreement with the growth VX-689 manufacturer mechanism we have proposed above. In order to investigate the effects of the different Cu concentrations on the optical characteristics in the yielded samples, we have carried out PL spectroscopy

as shown in Figure 6. We can see that all the samples show two emission peaks: a sharp one appearing at approximately 377 nm in the ultraviolet (UV) region and another broad one in the visible region. The former is ascribed to the near-band-edge (NBE) exciton recombination, while the latter is quite complicated due to the native and dopant-induced defects Dynein in ZnO. The intensive PL emission peak at 495 nm is suggested to be mainly due to the presence of various point defects, which can easily form recombination centers. The peak corresponding to 510 nm is usually generated by the recombination of electrons in singly ionized oxygen vacancies with photogenerated holes in the valence band [36, 37]. Apart from the strong peaks at 495 and 510 nm, the visible band consists of at least four sub-peaks at wavelengths of 530, 552, 575, and 604 nm, resulting from the local levels in the bandgap of ZnO. The green shoulders at 530 and 552 nm are attributed to the antisite oxygen and interstitial oxygen, respectively [35]. The peak at 604 nm is possibly caused by the univalent vacancies of zinc in ZnO. The origin of another peak at 575 nm has been rarely mentioned and is still unclear.