Third order nonlinear optical properties of undoped and Bi-doped ZnO-ZrO2 nanocomposites

Undoped and Bi doped ZnO – ZrO₂ nanocomposites (NCs) at various concentrations (5%, 7% and 9%) were synthesized using precipitation method. All samples underwent calcination at 500°C for 4 h and their structural, elemental, morphological, and optical characteristics were comprehensively investigated. The X-ray diffraction (XRD) pattern revealed a monoclinic phase due to the incorporation of Zirconium (Zr). The crystallite size of undoped, 5%, 7%, and 9% Bi-doped ZnO – ZrO₂ nanocomposites were determined as 41.10 nm, 35.89 nm, 34.53 nm and 29.73 nm respectively. Field emission scanning electron microscopy (FE – SEM) and elemental dispersive study (EDS) affirmed the successful incorporation of bismuth into ZnO – ZrO₂ system. Furthermore, elemental mapping confirmed the even distribution of Zn, Zr and bismuth in the prepared nanocomposites. Linear optical absorption spectra for undoped and Bi-doped samples were obtained using UV diffused reflectance spectroscopy (UV–DRS). The optical energy band gap (Eg) was calculated employing Kubelka – Munk theory exhibiting variations in the direct band gap among the synthesized nanocomposites due to Bi doping. Photoluminescence spectrum provided characteristic peaks for undoped, 5%, 7% and 9% Bi doped ZnO – ZrO₂ nanocomposites.The nonlinear optical response of these samples is investigated using Z-scan technique with nano pulsed Nd: YAG laser. Compared to undoped material, the 9% Bi doped nanocomposite exhibits a robust optical limiting threshold (1.41×10¹² m/W²) suggesting its potential application in laser safety devices.