Titanium dioxide nanoparticles have been synthesized by the chemical co-precipitation technique and then they have been coated with zinc oxide shell layers using a refluxing method to form TiO2/ZnO core/shell nanoheterojunctions. The physicochemical properties of as-synthesized core/shell nanoheterojunctions have been examined using X-ray diffraction (XRD), Fourier transfer infra-red spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). Photoluminescence (PL) emission spectroscopy has been carried out to analyze the linear optical characteristics at an excitation wavelength of 270 nm. A red shift towards longer wavelengths has been detected in NBE-related energies of TiO2/ZnO core/shell nanoheterojunctions compared to the sole TiO2 nanostructures. Third-order nonlinear optical studies have been performed by a single-beam Z-scan technique using a pulsed Nd-YVO4 laser system at a wavelength of 1064 nm. Third-order nonlinear refractive indices have been estimated as 10–12 m2/W. The sign of nonlinear refractive indices has been found to be negative, indicating self-defocusing behavior in the near infra-red region.

中文翻译：

---

TiO2/ZnO核/壳纳米球的线性和红外非线性光学特性的合成、表征和研究

二氧化钛纳米粒子是通过化学共沉淀技术合成的，然后用回流方法包覆氧化锌壳层，形成 TiO2/ZnO 核/壳纳米异质结。已使用 X 射线衍射 (XRD)、傅立叶转移红外光谱 (FT-IR)、场发射扫描电子显微镜 (FESEM)、能量色散光谱 (EDS) 检查合成的核/壳纳米异质结的理化性质和透射电子显微镜（TEM）。已经进行了光致发光 (PL) 发射光谱分析，以分析 270 nm 激发波长下的线性光学特性。与单一的 TiO2 纳米结构相比，已在 TiO2/ZnO 核/壳纳米异质结的 NBE 相关能量中检测到向更长波长的红移。三阶非线性光学研究已通过使用波长为 1064 nm 的脉冲 Nd-YVO4 激光系统的单光束 Z 扫描技术进行。三阶非线性折射率估计为 10–12 m2/W。已发现非线性折射率的符号为负，表明在近红外区域存在自散焦行为。