Third-order non-linear spectroscopy of CdSe and CdSe/ZnS core shell quantum dots

The third-order non-linear optical properties of CdSe and CdSe/ZnS core-shell quantum dots in solution with toluene were studied over a spectrum ranging from 450 to 680 nm using 225-fs pulses. The electronic and thermal contributions to the non-linearity, leading to positive or negative non-linear refractive indices, are investigated. Although the sign and magnitude of the non-linearity vary with wavelength, it was found to be of the same order of magnitude as that of bulk CdSe for the same photon energy-to-band gap ratio. However, because the absorption edge of CdSe quantum dots is blue-shifted relative to bulk, it permits fast optoelectronic applications in the visible spectrum by avoiding slow thermal effects normally associated with linear absorption.