Photoluminescence studies of silver-exchanged cadmium selenide crystals. Modification of a chemical sensor for aniline derivatives by heterojunction formation

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. The ESCA and Auger spectroscopy are consistent with the formation of Ag2Se islands having thicknesses of 0 to 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.