Nonlinear optical response of ZnO/HfO2 core/shell nanorod arrays under continuous wave laser irradiation

ZnO nanorods (NRs) were synthesized by the hydrothermal method and coated by HfO2 sell layers by using the atomic layer deposition to form ZnO/HfO2 core/shell NRs arrays. XRD showed the hexagonal wurtzite structure of ZnO NRs and tetragonal phase of HfO2. Scanning electron microscope and atomic force microscopy analysis illustrated vertically well-aligned ZnO/HfO2 core/shell NRs structure. Optical property was studied by PL which revealed that the near band-edge emission of the ZnO NRs improved after coating by HfO2 shells. The band gap energy was estimated about 3.51 eV by UV–Vis. For the first time, the measurements of nonlinear optical (NLO) properties of ZnO/HfO2 core/shell NRs structures have been performed by using a continuous-wave (cw) Nd:YAG laser at 532 nm by the Z-scan technique. A negative nonlinear refractive index and a positive absorption coefficient were calculated equal to 8.6 × 10−6 cm2/W and 1.75 cm/W for ZnO/HfO2 core/shell NRs, respectively. A third-order NLO susceptibility of ZnO/HfO2 core/shell NRs was measured of the order of 10−2 esu which is a large value. The results suggest that ZnO/HfO2 core/shell NRs are promising candidates for NLO applications.