CdS Q-nanoparticles were obtained by using n-octylthiol or dodecyl mercaptan as surface modifier, and Q-CdS/polymer nanocomposite films were gotten by mixing CdS Q-nanoparticles with polymer.Surface modification of Q-CdS with mercaptan and polymer was studied by fluorescent spectra.It was found that long carbon chain of mercaptan could effectively prevent the Q-CdS from reuniting and strengthen the stability of Q-CdS.The intensity of exciton emission peak (420 nm) in Q-CdS was increased as the carbon chain of mercaptan became longer.As the ratio of mercaptan to Cd²⁺ was changed, the intensity of exciton emission peak was also changed and the strongest emission intensity was gotten at certain ratio of mercaptan to Cd²⁺.Due to the dielectric local effect the intensity of surface emission peak (550 nm) in Q-CdS became 10 times stronger with the dispersion of Q-CdS nanoparticles into polymer than that of the single CdS Q-nanoparticle solution.On the other hand, with increase of the polymer content the intensity of surface emission peak in Q-CdS became to decrease reversely.Correspondingly the exciton emission peak began to appear and was gradually strengthened.It is because the polymer passivated the surface of Q-CdS and reduced the surface defect.

Key words: CdS Q-nanoparticle, surface modification, mercaptan, fluorescence, polymer