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 Cd2+ plating solution using a train of 8-10 ms plating pulses separated by approximate to 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 H2S at 300 degrees 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.