Facile synthesis and large third-order optical nonlinearity of Manganese-loaded mesoporous silica thin films

An in-situ reduction method is adopted to incorporate MnO2 nanoparticles into mesochannels of silica thin films by using KMnO4 as the oxidizing agent and manganese precursor. As the reduction time in KMnO4 solution increases, the ordered mesostructure collapses, and the loaded MnO2 nanoparticles become bigger in size, resulting in a narrower band gap. Z scan measurement demonstrates a large third-order nonlinear susceptibility of the composite films under the picosecond Nd:YAG laser excitation. A sign reversion of the third-order nonlinear refractive index coefficient in the sample with longer reduction time is also observed, which can be attributed to the variation in the band gap energy.