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.