Abstract

We measured the values of the first hyperpolarizability β for aqueous suspensions of CdS nanoparticles by a Hyper-Rayleigh scattering (HRS) technique. The samples consisted of nanoparticles with three types of surface: as-prepared (Cd⁺²-rich surface stabilized by polyphosphate), modified by OH^–, and Pt-loaded. The CdS suspensions were prepared by a method modified from Ref. [1]. The surface modifications were based on procedures published in the literature. The samples were characterized by UV-visible absorption spectroscopy and by transmission electron microscopy (Carl Zeiss, TEM 902 - 80keV). The nanoparticle sizes were estimated from UV-visible absorption spectra using the well-established relationship between absorption and size for particles in the quantum confinement regime. The β values were determined from HRS measurements using a Q-switched Nd-YAG laser, which delivered 10 ns, up to 60 mJ pulses at 1064 nm. The beam radius inside a cell with the samples was about 1.5 mm The samples were filtered through a 0.45 µm Teflon filter prior to the measurements. The orientation averaged hyperpolarizability <β²> was determined from the intensity of the doubled frequency light by external and internal reference methods. The reference material was a methanolic solution of para-nitroaniline (concentration 10²⁰cm^-3). We assumed that despite the different point symmetry of the species used by measurements, the main contribution into <β²> is due to the component βzzz.

© 2000 IEEE