Nonlinear refraction and nonlinear absorption of CdSe0.3S0.7/ZnS quantum dots

Nonlinear optical properties of CdSe0.3S0.7/ZnS quantum dots(QDs) were investigated by Z-scan technique using the Nd:YAG laser second harmonic radiation (λ=532 nm, t=35 ps). The Z-scan results show that the CdSe0.3S0.7 QDs have strong reverse saturable absorption(RSA). Based on the linear absorption spectrum and one-photon resonant fluorescence spectrum, it is reasonable for us to infer that the nonlinear absorption arises from free carrier absorption(FCA). Based on standard Z-scan theory, we obtain the FCA cross section and nonlinear refractive index of CdSe0.3S0.7/ZnS QDs. These QDs have average absorption cross section of 2.8×10−16 cm2 and nonlinear refractive index on order of 10−7 esu. The strong nonlinear absorption and large nonlinear refractive index perhaps allow them to be applicable in the optoelectronic field.

Graphical abstractA mechanism for RSA of CdSe0.3S0.7/ZnS QDs under the ps laser pulse.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► In this letter, we investigated their nonlinear optical properties by Z-scan technique using 532 nm laser pulse for the first time. ► Free carrier absorption(FCA) cross section of CdSe0.3S0.7/ZnS QDs was obtained. ► These QDs exhibit excellent optical limiting performance. ► Their large nonlinear absorption and nonlinear refraction may allow them to be applied in the optoelectronic field.