Linear and nonlinear optical properties of Co3O4 nanoparticle-doped polyvinyl-alcohol thin films

Thin films made from a composite of the polymer polyvinyl-alcohol and cobalt oxide (Co3O4) nanoparticles were fabricated by spin coating. Linear and nonlinear optical properties of thin films with thicknesses of hundreds of nanometers were investigated. The refractive index and absorption coefficient were measured and two direct band gaps (E-g = 1.38 eV and 2.0 eV) were determined from the absorption spectrum. Reversed saturable absorption and saturable absorption were observed when the films were illuminated with the different fluences. Optical nonlinearities corresponding to reverse saturable absorption were measured by the z-scan technique. A nonlinear refractive index (n(2)) of similar to 10(-10) cm(2)/W and nonlinear absorption (beta) of similar to 10(3) cm/GW have been measured from 425 nm to 675 nm. The experimental results show that the Co3O4 nanoparticle/PVA composite is a promising material for nonlinear optical devices in the visible, since it takes advantages of the high optical nonlinearities of transition metal oxides and the superior mechanical properties and convenient fabrication properties of polymers. (C) 2011 Optical Society of America