We analyze the features of nonlinear refraction in colloidal solutions containing Ag₂S quantum dots capped with thioglycolic acid (Ag₂S/TGA) or L-cysteine (Ag₂S/L-Cys), with the quantum-dot (QD) sizes ranging from 1.7 to 5.5 nm and their concentration in the solution being 0.1%. The Z-scans of the samples were obtained using 10 ns pulses of 532 nm radiation. For samples with various average sizes and positions of the characteristic feature in the optical density spectrum, both self-focusing and self-defocusing of radiation were observed. The contribution of thermal refraction to the recorded Z-scans was estimated, and the impact of thermal effects on the observed nonlinear refraction was shown to be negligible. The solutions of the Ag₂S/TGA QDs with the ground state exciton absorption peaked at 590 nm exhibit self-focusing. The samples with recombination luminescence and the ground state exciton absorption peaked at 750 nm reveal self-defocusing. We show that nonlinear refraction in the case of nanosecond pulses is predominantly nonthermal in nature and is due to absorption by free charge carriers, as well as due to the band filling effect in the Ag₂S QDs, which involves localized states of impurities.

我们分析了含有巯基乙酸（Ag ₂ S / TGA）或L-半胱氨酸（Ag ₂ S / L-Cys）封端的Ag ₂ S量子点的胶体溶液的非线性折射特征，量子点（QD）大小范围为1.7至5.5 nm，溶液中的浓度为0.1％。使用532 nm辐射的10 ns脉冲获得样品的Z扫描。对于具有各种平均尺寸和特征特征在光密度谱中的位置的样品，观察到辐射的自聚焦和自散焦。估计了热折射对记录的Z扫描的贡献，并且热效应对观察到的非线性折射的影响显示为可忽略的。Ag ₂的解决方案具有在590 nm处达到峰值的基态激子吸收的S / TGA QD表现出自聚焦。具有重组发光和在750 nm达到峰值的基态激子吸收的样品显示出自散焦。我们显示，在纳秒脉冲的情况下，非线性折射本质上主要是非热的，并且归因于自由电荷载流子的吸收，以及归因于Ag ₂ S QD中的能带填充效应，这涉及杂质的局部状态。