Large two-photon absorbance of chitosan-ZnS quantum dots nanocomposite film

ZnS semiconductor nanoparticles with average size of 3.4 nm were prepared in situ in chitosan film. TEM, UV-vis spectra and PL spectra show the ZnS nanoparticles in chitosan template were monodispersed and well passivated. The two-photon absorption coefficient (β) of the chitosan-ZnS quantum dots (QDs) nanocomposite film was obtained to be 2.29×102 cm/Gw from a standard Z-scan setup with femtosecond laser pusles at 790 nm wavelength. Results show the novel biomacromolecule/QDs nanocomposite film has large third-order optical nonlinear absorption, the mechanism responsible for which was discussed.