Optical properties of gold-silver iodide nanoparticle pair structures

Nanoparticle pair structures composed of metal (Au) and semiconductor (AgI) segments with radii ca. 16 nm have been prepared in porous anodic aluminum oxide via electrochemical template synthesis. The metal and semiconductor members can be prepared such that they are in contact or separated in the porous host. UV/ visible spectra of composites in which the Au and AgI segments are in contact show a red-shifted and broadened Au particle plasmon resonance band and the absence of the AgI exciton peak normally observed at lambda = 425 nm. A blue shift in the Au particle plasmon band and the reappearance of the AgI exciton peak occur as the average interparticle spacing is increased. The changes in plasmon resonance peak position are consistent with an increased probability of Au and AgI intermixing as the spacing parameter d(12) is decreased. The absence of the AgI exciton peak in the case of contacting An and AgI particles is consistent with a large increase in the effective static dielectric constant upon phase intermixing and/or field effects associated with the contact potential at the Au/AgI interface.