Effect of heat treatment on the photoluminescence of CdS nanocrystallites in cadmium-rich organic Langmuir Blodgett matrix

CdS nanocrystallites were grown within an organic layered matrix by partial sulphidation of precursor cadmium arachidate LB multilayers. The cadmium arachidate-arachidic acid composite multilayers containing CdS nanocrystallites were enriched by intercalation with Cd2+ ions in aqueous solution of CdCl2 and subsequently heat treated at different temperatures up to 300 degrees C, in air and in vacuum. CdS nanocrystallites within the composite multilayer have been found to exhibit treatment process dependent characteristic changes in optical absorption and luminescence. The optical data obtained at different stages/conditions of processing have been analyzed by considering changes in excitonic absorption and emission as well as contributions from surface and bulk defects related emission and a suitable energy level diagram has been proposed. The composition, microstructure and surface morphology of the composite multilayers were also studied at all stages of processing to develop a comprehensive understanding of the interaction of the organic matrix with CdS nanocrystallites and the consequent influence on the optical behavior of the nanocrystallites. These studies have shown that the organic moieties encapsulating the CdS nanocrystallites tend to restrict their growth and aggregation, while the presence of cadmium in the organic matrix is responsible for the passivation of surface defects as well as the reduction of bulk defects, and these factors have significant influence on the photoluminescence of CdS nanocrystallites. (C) 2013 Elsevier B.V. All rights reserved