A feasible approach for synthesis of emissive Fe:CdS colloidal nanocrystals and their microstructural and spectroscopic properties

Abstract

Colloidal semiconductor nanocrystals have recently gained increasing research interest due to their unique optical properties. Herein, we demonstrate a facile and feasible strategy for the synthesis of highly luminescent and water-soluble Fe:CdS nanocrystals at mild conditions in an aqueous solution with the aid of small molecular ligand thioglycolic acid without using any environmentally hazardous organic chemicals. The formation of Fe:CdS nanocrystals and their structure, morphology and elemental composition were thoroughly explored by means of X-ray diffraction, transmission electron microscopy, and Energy-dispersive X-ray spectroscopy. The Fe:CdS nanocrystals crystallize well, and exhibit zinc blende crystal structure of cubic CdS with an average particle size of ca. 3nm. The presence of thioglycolic acid on the surface of Fe:CdS nanocrystals was evidenced by Fourier transform infrared spectroscopy. The absorption onsets of the resulting nanocrystals are blue-shifted with respect to the corresponding band gap of bulk CdS due to the quantum confinement effect. We demonstrate that the particle sizes and optical properties of the Fe:CdS nanocrystals could be readily engineered by tuning the starting pH values of the reaction solution. These nanocrystals show intense emission features, and the maximum luminescent intensity of the samples can be attained when the starting pH value is ca. 9. Furthermore, the proposed mechanism for the pH-dependent optical properties of the Fe:CdS nanocrystals is also presented. We believe that these nanocrystals may find broad uses in biolabeling, biosensing, light-emitting diodes, and other nanodevice applications. Moreover, this strategy presents an alternative which is adaptable for mass production and can be easily employed to synthesize a variety of doped and alloyed nanocrystals.