Ultrasmall particles of CdSe and CdS formed in Nafion by an ion-dilution technique

The transition of semiconductor chalcogenides from molecular CdX (X = Se, S) to bulk material has been observed in Nafion, a cation-exchange membrane. The two-phase structure of Nafion, consisting of a hydrophobic region and ionic clusters, has been utilized to form ultrasmall particles of CdS/Se by using a technique analogous to an inverted micelle microemulsion method, where the Cd ion/ionomer cluster ratio is controlled by diluting the cadmium-exchange solution with an inert ion (Ca²⁺). The absorption onset for the cadmium chalcogenides formed can be tuned over a range of more than 3.5 eV by varying the Cd²⁺/Ca²⁺ ratio in the solution used to exchange the acidic form of the ionomer membrane.