EFFECTS OF SURFACE CONDITIONS ON THE LUMINESCENCE OF COLLOIDAL CADMIUM-SULFIDE

The luminescence (so-called green emission or edge emission, corresponding to the band gap energy) of colloidal cadmium sulphide solutions (prepared by the introduction of hydrogen sulphide gas over the surface of aqueous cadmium nitrate solutions containing sodium hexametaphosphate as stabilizer to prevent the flocculation of the colloid) was studied. The luminescence was strongly affected by the amount of hydrogen sulphide gas introduced into the solution: the Cd2+-rich (S2--deficient) colloid showed much stronger luminescence than the S2--rich colloid. The luminescence was also influenced by the pH of the solution and the addition of ethylenediaminetetraacetate (EDTA). The addition of a small amount of EDTA strongly quenched the luminescence of Cd2+-rich solutions irrespective of the pH. For S2--rich solutions, EDTA had no effect on the edge emission at low pH, but increased its intensity at high pH. These results can be explained by the pH-dependent chelating ability of EDTA.