Substantial effect of Cr doping on the third-order nonlinear optical properties of ZnO nanostructures

Abstract

Here in, the present work we report the influence of Cr doping on the nonlinear properties of hydrothermally prepared ZnO nanoparticles. Structure has been confirmed from XRD analysis and exhibit a hexagonal wurtzite structure. Observed peak shift and decrease in crystallite size observed from XRD analysis confirms the successful Cr doping. FE-SEM images show distorted rod-like morphology and the doping percentages are confirmed from the EDAX spectra. The XPS spectrum confirms the existence of oxygen vacancies, which validates the existence of divalent oxidation states of zinc and the trivalent state of chromium. The calculated bandgap values validate thatZn0.98Cr0.02O nanoparticles exhibit the lowest bandgap energy due to the presence of optically active sub-levels within the bandgap region. Variation in peak intensity was observed from the Raman spectra, which validates the addition of Cr into lattice sites of ZnO. Under continuous wave (CW) laser regime, the Z-scan method was used to determine the third order nonlinearity and demonstrate, Zn0.96Cr0.04O nanoparticle show a combined effect of saturable absorption (SA) and reverse saturation absorption (RSA) under open aperture measurements with an increase in nonlinear absorption coefficient (βeff), and third-order NLO susceptibility (χ(3)) values on increasing Cr3+ doping concentration.