CdS/ZnS Quantum Dots

Semiconductor nanocrystal quantum dots have been investigated in different aspects from physical properties of low-dimensional systems to their potential applications. QDs have demonstrated excellent optical properties and higher photochemical stability than most organic emitters. Their broad absorption spectrum and narrow emission band would be tunable by changing their size. One of the most interesting applications is the use of quantum dots as luminescent labels for optical sensors or fluorescent label sources for biological imaging applications.

Zinc sulphide (ZnS) and cadmium sulphide (CdS) are II-VI semiconductors with direct band gap of 3.68 eV, 2.42 eV respectively in bulk form. Particle size must be less than twice of Bohr radii of exciton as quantum confinement regime is limited to that size. The tunability of the properties of nanoparticles by controlling their size may provide an advantage in formulating new materials with optimized properties for various applications.

Quantum dots are considered as potential candidates for solar cell applications due to quantum confinement effect. CdS/ZnS core-shell structure formed by capping of a CdS core, with a thin ZnS shell. The formation of ZnS shell can greatly passivate the core surface to protect it from oxidation and prevent CdS leaching into the surrounding medium and also improve the photoluminescence yield and photo-stability.

The high photochemical stability of high luminescence-intensity and biocompatibility of CdS/ZnS core/shell QDs make them suitable for optoelectronic devices and some biological applications.

CdSZnS Core Shell Nanoparticles: The photoluminescence intensity and the photostability of CdS/ZnS quantum dots is increased in comparison with CdS quantum dots without the ZnS shell. The core-shell technique of the generation of binary QDs provides a significant increase in the emission intensity without any shift of the emission wavelength.