Surface effects on regularities of electron transfer in CdS and CdS/Cu2S colloids as studied by photoluminescence quenching

CdS colloids of different sizes were prepared using two different-methods: either with an excess of S2- ions or with an excess of Cd2+ ions. The shape of the luminescence spectra and regularities of luminescence quenching hav e been studied for both colloids. It has been found that positively charged electron acceptor molecules (bication of methyl viologen) effectively quen ch the luminescence of the colloids with the S2- ions excess and practicall y do not quench the luminescence of the colloids with the Cd2+ ions excess; Vice versa, negatively charged electron acceptor molecules (anions of hete ropolyacids) effectively quench the luminescence of the colloids with exces sive Cd2+ ions and do not quench the luminescence of the colloids with exce ssive S2- ions. The observed phenomenon can be explained easily by taking i nto account the necessity of adsorption of the quencher molecules on the su rface of semiconductor particles in the electron-transfer process. It has a lso been observed that for both types of colloids the efficiency of the lum inescence quenching is related to the luminescence wavelength. The regulari ties of the luminescence quenching have been studied for the CdS colloids o f different sizes coated with CuxS as well. It was observed that the additi on of copper ions increases the efficiency of luminescence quenching by met hylviologen (MV2+) and tungstophosphoric heteropolyacid (PW12). Moreover, t he shape of the luminescence spectra of these coated colloids depends on th e excitation wavelength, the increase of the excitation wavelength resultin g in the shift of luminescence spectra to the "red" region.