Synthesis of trap emission free cadmium sulfide quantum dots: Role of phosphonic acids and halide ions.

Changing the capping ligands of CdS nanocrystals during their synthesis controls the optical properties of these nanocrystals. Addition of a little amount of CdCl2:Phosphonic Acid (PA) completely eliminates the surface state emission with an increase in quantum yield of band edge emission from these nanocrystals. The role of halide ions in surface passivation along with the structural dependance of these nanocrystals on surface states has also been studied. These as prepared nanocrystals are uniform as well as monodispersed and their size can be tuned by varying the reaction time. These nanocrystals have been well characterized using a combination of optical and structural techniques.