Colloidal CdSe–ZnS core-shell nanoparticles: Dependence of physical properties on initial Cd to Se concentration

Different sets of CdSe–ZnS core-shell colloidal nanoparticles are synthesized from the starting solution containing stoichiometric excess or deficit of metal counterpart (Cd to Se ratio) to study the variation in physical property depending upon the core composition. It is found that the stoichiometric variation in the starting solution affects the microstructure of the nanoparticles and hence the variation in absorption and emission properties. It is found that the band edge emission peak shifted to the lower energy levels with increasing Cd/Se ratio in the starting solution. Broadening of the Photoluminescence spectral shape is found for Cd rich or Se rich samples. The stoichiometric sample shows the brightest emission that can be associated with the lesser defects associated to the nanoparticles in that sample. Tailing of the optical absorption beyond the band edge is found to be least for the stoichiometric sample indicating fewer defects present in the sample.