Effects of Mn doping on the structural, linear, and nonlinear optical properties of ZnO nanoparticles

In this study, the synthesis and characterization of undoped and Mn-doped ZnO nanoparticles with 2%, 5%, and 15% Mn/ZnO prepared using the hydrothermal method were reported. The structural, morphological, and chemical-bond properties of the Mn-doped ZnO nanoparticles were studied by using x-ray diffraction, field emission scanning electron microscopy (FESEM), energy dispersive x-ray analysis, and Fourier transform infrared spectroscopy analysis. X-ray diffraction patterns indicate that all of the samples have hexagonal wurtzite structures. The average diameters of the Mn-doped ZnO nanoparticles with different Mn/ZnO ratios were estimated to be about 20–38 nm from the FESEM images. The linear absorption coefficient and optical band gap energy of ZnO and Mn-doped ZnO nanoparticles were calculated using UV-Vis spectroscopy. A decrease in Eg was observed by an increase in Mn concentration. The nonlinear optical measurements have been performed using a nanosecond Nd:YAG pulse laser by the Z-scan technique. Both the undoped and Mn-doped ZnO nanoparticles exhibited a negative nonlinear optical index of refraction at 532 nm relating to the self-defocusing phenomenon. The nonlinear optical absorption of ZnO and Mn-doped ZnO nanoparticles is attributed to two-photon absorption combined with free carrier absorption. Furthermore, the third-order nonlinear susceptibility values of the undoped and Mn-doped ZnO nanoparticles varied between 1.2−2.5×10−9  esu, depending on the Mn contents. The results suggest that a Mn dopant can improve the nonlinear optical properties of ZnO nanoparticles, and Mn-doped ZnO nanoparticles synthesized through the hydrothermal method may be a promising candidate for nonlinear optical applications at 532 nm.