Nonlinear optical properties of CdSe_0.8S_0.2quantum dots

The nonlinear optical properties of CdSe0.8S0.2 quantum dots(QDs) have been investigated by the Z-scan technique using Nd:YAG laser second harmonic radiation (λ = 532 nm, t = 35 ps). The Z-scan results show that the CdSe0.8S0.2 QDs have strong reverse saturable absorption (RSA), and the nonlinear absorption coefficient is approximately three orders of magnitude higher than that of CdSeS doped glass from a previous report. On the basis of the absorption and fluorescence spectra, it is reasonable for us to infer that the nonlinear absorption arises from free-carrier absorption (FCA). These QDs have average absorption cross section of 1.70 × 10−16 cm2 and nonlinear refractive index on the order of 10−8 esu. The excellent nonlinear optical properties perhaps allow CdSe0.8S0.2 QDs to be one kind of candidate material for optical limiting and all-optical switching devices.

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