Cd1−xZnxS nanoparticles stabilized by a bifunctional organic molecule

We have prepared Cd1−xZnxS quantum dots capped with bifunctional molecule mercaptoacetic acid. UV–vis absorption shows an increase of band gap as Zn substitutes Cd; the absorption band shifts from 331 nm (x=0) to 295 nm (x=1). We have calculated the size differences of CdS and ZnS quantum dots and correlate them to the electron density at sulfur atoms and ligand bond lengths of CdS and ZnS. Photoluminescence emission of CdS shows a sharp peak at 363 nm and broad band at around 428 nm, whereas ZnS shows the sharp peak at 331 nm and a tail at around 415 nm. The behavior of surface state emission with respect to band-edge emission for CdS and ZnS has been investigated and explained in terms of the surface per volume ratio of the two nanocrystals. The band-edge emission of CdS nanoparticles has been found to depend on the excitation energy. The trap state emission bands of CdS and ZnS and effect of excitation energy on the position of these bands have been studied.