Effect of temperature and etching under light irradiation on the band edge emission of β-mercaptoethanol-capped CdS colloidal nanocrystals

In this work, cadmium sulfide nanocrystals capped with β-mercaptoethanol: CdS–βME (NCs) formed at wurtzite structure were prepared by colloidal chemical method for structural and optical properties' investigation. The temperature dependence of the photoluminescence (PL) intensity and its quantum yield (QY), the PL pic position and FWHM and the PL lifetime were systematically studied over a broad temperature range of 10–300 K. PL enhancement, photoetching and photostability of CdS–βME NCs were investigated under light irradiation. XRD and TEM patterns showed that CdS–βME NCs have an hexagonal phase with wurtzite structure. A very narrow excitonic blue emission peak with relatively high intensity was detected, which is similar to the better results obtained via organic synthesis. The FWHM (\(\sim\) 20 nm) is controlled by an inhomogeneous broadening due to the particle size/morphology distributions of the NCs. Dynamic studies reveal shorter lifetimes indicating weak contribution of the surface-related emission with the removal of surface defects. The photoetching process of CdS–βME NCs resulted in a high QY of up to 3.8% with an obvious blueshift in band emission. On the basis of these studies, it is established that the surface of CdS–βME is rich with Cd²⁺ ions, leading to the formation of a CdO layer as shell, which provides a better passivation by removing surface hole traps and confines the charge carriers with illumination by Hg lamp radiation. In conclusion, owing to their excellent dispersibility in water and high luminescence, the CdS–βME NCs that have been developed here can be a promising candidate for biolabelling and imaging applications.