Nonlinear optical characterisation of CdS and PbS quantum dots dispersed in a glass matrix

We report on the third- order nonlinear optical properties of sol-gel prepared CdS quantum dots (with different thermal treatments, filling factors and matrix), and commercial Schott filters (CdSSe nanodots), compared to a bulk CdS crystal. Also PbS quantum dots have been characterised. The spectral dispersion of third-order nonlinear optical response of the samples has been determined by third harmonic generation (THG). By taking into account the dots concentration and appropriate local field correction factor, we have been able to extrapolate a renormalised nonlinear coefficient for the dots, which can be directly compared to the nonlinear coefficient of the forming bulk constituents. In the out-of-resonance regime, no intrinsic enhancement of the nonlinear coefficient due to quantum confinement has been detected for any sample, with respect to the bulk constituent. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)