Defect state enhanced third order thermo-optic nonlinearity in Bi3+ doped MnWO4 nanostructures

We present the third order nonlinear optical characteristics of Bi³⁺ doped MnWO₄ nanostructures synthesized by chemical precipitation technique. The structural information revealed by X-ray diffraction (XRD) and Raman analysis confirmed the incorporation of Bi³⁺ ions into the MnWO₄ lattice with no secondary phases. UV–Vis absorption spectra evidences the absorbance maximum in the UV region and the particles are feebly transparent in the visible region. The inclusion of Bi³⁺ in MnWO₄ was further confirmed by Photoluminescence quenching. The calculated particle sizes from Transmission electron microscope (TEM) were found to be 30–50 nm. The chemical composition and oxidation states of Bi³⁺ doped MnWO₄ nanostructures is confirmed by X-ray photo electron spectroscopy (XPS). A continuous wave Nd: YAG laser operated at 532 nm was used to analyze the third order nonlinear optical behavior of Bi³⁺ doped MnWO₄ nanostructures by Z-scan technique. Analysis of both open and closed aperture experimental data reveals that reverse saturable absorption and self-defocussing effect is the cause of observed nonlinearities. The optical nonlinearity of the nanostructures is found to be increased upon Bi³⁺ concentration. Based on the observed nonlinearities, the synthesized nanostructures are capable of potential application in photonic devices.