Optical and nonlinear optical properties of surface-modified CdS nanoparticles

Hyper-Rayleigh scattering (HRS) technique was used to measure the first-order hyperpolarizability, β, of CdS nanoparticles with different surface-modifying agents (anion of surfactant bis (2-ethylhexyl) sulfosuccinate, disodium salt (named as AOT-SO3−) and pyridine). The ‘per particle’ (4 nm mean diameter) β-values are estimated to fall in the range of 10−27 esu, which is among the largest values reported for solution species and the β-value of pyridine-modified CdS is 1.4-times smaller than AOT-SO3−-modified CdS. As a possible explanation, this difference in the β-values is attributed to the weakening of the two-photon resonance enhancement effect in the pyridine-modified CdS nanoparticles due to the σ-donation formation of pyridine to the Cd2+-rich surface of CdS. These were demonstrated by two-photon fluorescence measurements, one-photon fluorescence quenching experiments and photolysis experiments.