Structural and optical response of mixed phase CdS nanocrystals to Ni2+ ions

Cadmium sulfide (CdS) semiconductor nanocrystals doped with Ni2+ have been synthesized via a solution-based method and employing 2-mercaptoehonal as a capping agent. The obtained nanocrystals were characterized using X-ray diffraction (XRD) and Diffuse reflectance spectroscopy studies (DRS). XRD results showed that the undoped CdS nanocrystals are in mixed phase of cubic and hexagonal, where as the doped CdS nanocrystals in hexagonal phase. DRS results supported the mixed phase of undoped nanocrystals by showing two absorption edges at 363 nm and 428 nm. The absorption edge at 363 nm can be attributed to cubic phase while the other can be attributed to hexagonal phase of the sample. But for Ni2+ doped CdS nanocrystals only one absorption edge at 468 nm was observed. The observed red shift in the band edge of the nickel doped CdS nanocrystals is due to sp-d exchange interactions between the band electrons and the localized d-electrons of the Ni2+ ions substituting Cd2+ ions in the doped sample.