Two-photon absorption and two-photon assisted excited-state absorption in CdSe0.3S0.7 quantum dots

CdSe0.3S0.7 quantum dots (QDs) with a diameter of about 4 nm were synthesized by a chemical route. The two-photon absorption (TPA) and two-photon assisted excited-state absorption (TPESA) of these QDs were investigated at the wavelength of 532 nm using a picosecond laser in an open-aperture Z scan setup. The TPA cross section for these nanoparticles is about 3.7 x 10(6) GM, which is several orders of magnitude larger than that for a conventional fluorescence probe. The TPESA cross section is on the order of magnitude of 10(-19) cm(2). These optical properties of the QDs may allow them to be applied in optoelectronic and biological fields.