Size dependence of nonlinear optical properties of PbS QDs, passivated with thioglycolic acid

The size dependence of the nonlinear optical response of hydrophilic colloidal PbS quantum dots, passivated with thioglycolic acid (PbS/TGA QDs) with an average size of 3.0, 3.5, 4.5 nm in the field of 10 ns laser pulses at 532 nm has been analyzed. It is shown that the key mechanism of nonlinear absorption is the reverse saturable absorption, which occurs with involvement of QDs defect trap states. The formation of SiO2 monolayer on the PbS/TGA QDs surface, using MPTMS makes it possible to significantly increase in the luminescence intensity from 4 to 4.5 times. In this case, the nonlinear absorption coefficient and nonlinear refraction index do not change. The facts indicate the implementation of a nonlinear optical response in the nanosecond probe pulse range on trap states that are not luminescence centers.