Third-Order Nonlinear Optical Properties of Infrared Emitting PbS and PbSe Quantum Dots

The optical properties of small band gap, colloidal quantum dots are presented, with the special emphasis put on the measurements of their nonlinear optical properties in the infrared region of spectra. In particular, two types of colloidal quantum dots (PbS and PbSe), with the first exciton absorption band maxima in the near-infrared region of spectra, were investigated using a tunable femtosecond laser system and the Z-scan technique. The measurements of closed- and open-aperture Z-scan traces allowed for the calculation of real and imaginary parts of cubic nonlinearity, which were presented as appropriate cross sections used to characterize the nonlinear refractive and absorptive properties of the studied quantum dots. The maximum two-photon absorption cross section values taken for a single quantum dot were found to be ∼2400 GM (Goeppert-Mayer units) at 1300 nm and ∼15 500 GM at 1700 nm, for PbS and PbSe QDs, respectively. PbS quantum dots showed two-photon induced emission upon infrared excitation. The obtained results demonstrate the potential of IV–VI group colloidal quantum dots for low-cost photonic devices and two-photon absorbers in the near-infrared and infrared spectral ranges.