Surface-related two-photon absorption and refraction of CdSe quantum dots

Colloidal CdSe quantum dots (QDs), whose surface traps are controlled with the purification process, are measured with a Z-scan technique using an 80 femtosecond pulse duration laser source. Their two-photon absorption coefficient and refractive index are decreased more than one order of magnitude with the increase of the density of surface traps, indicating that the surface states are involved in the two-photon process. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3610561]