Photoluminescence Studies of Silver-Exchanged Cadmium Selenide Crystals. Modification of a Chemical Sensor for Aniline Derivatives by Heterojunction Formation

Abstract : Single-crystal n-CdSe surfaces have been modified by an exchange reaction with aqueous Ag+ that converts part of the surface to Ag2Se and releases Cd2+ to solution. Formation of Ag2Se is established by X-ray powder diffraction. ESCA and Auger spectroscopy are consistent with the formation of Ag2Se islands having thicknesses of 0-500 A, depending on reaction conditions. Steady-state photoluminescence (PL) experiments show that Ag+-exchanged CdSe (CdSe/Ag+) can be superior to CdSe as an aniline sensor: ring-substituted aniline derivatives in toluene solution cause enhancements of the CdSe band edge PL in CdSe/Ag+ samples relative to a toluene ambient, with the effect about twice as large as for unexchanged CdSe. The variations in PL intensity of CdSe/ Ag+ are well fit by a dead-layer model, allowing estimation of the adduct- induced change in depletion width.