“Multipulse” Electrochemical/Chemical Synthesis of CdS/S Core/Shell Nanocrystals Exhibiting Ultranarrow Photoluminescence Emission Lines

Ensembles of sulfur capped, cadmium sulfide nanocrystals (CdS/S NCs) which exhibit photoluminescence (PL) emission line widths of 15−35 meV at 20 K have been obtained. These CdS/S NCs were synthesized using a new variant of the electrochemical/chemical (E/C) method: Cadmium (Cd o ) NCs were first electrodeposited from an aqueous Cd 2+ plating solution using a train of 8−10 ms plating pulses separated by ≈1.0 s “mixing” segments at the open circuit potential. These Cd o nanoparticles were then oxidized to Cd(OH) 2, and CdS/S NCs were obtained by exposure of Cd(OH) 2 nanoparticles to H 2 S at 300 °C. Ensembles of 200 000−400 000 CdS/S NCs prepared using this “multipulse” technique exhibited PL emission lines narrower than 35 meV. CdS/S NCs were also synthesized using the same E/C method except that a single Cd o plating pulse was employed, and these CdS/S NCs exhibited PL emission line widths of 125−180 meV. TEM analysis of Cd(OH) 2 precursor particles confirms that the narrower lines obtained using multipulse Cd o electrodeposition result from improved size monodispersity of the CdS core, which is attributed to the diffusional decoupling of Cd o nanoparticles during growth.