Upconversion photoluminescence of CdS nanocrystals in polymeric film

We report on nonlinear upconversion photoluminescence (PL) of CdS nanocrystals (NCs) embedded in a polymeric film. The CdS NCs of 2 nm radius are synthesized by an ion exchange method and highly concentrated in the two layers near the surfaces of a freestanding Nafion film. We observed the differences between the two-photon and one-photon excited PL emissions. The two-photon absorption cross section and quantum yield of CdS NCs were measured with femtosecond laser pulses at 800 nm excitation. The origin of PL, optical nonlinearity, and the figure of merit for optical switching have been discussed. (C) 2008 American Institute of Physics.