Core–shell semiconducting nanocrystals are a class of materials which have properties intermediate between those of small, individual molecules and those of bulk, crystalline semiconductors. They are unique because of their easily modular properties, which are a result of their size. These nanocrystals are composed of quantum dot of semi-conducting core material and a shell of a distinct semiconducting material. The core and the shell are typically composed of type II–VI, IV–VI, and III–V semiconductors.

The properties of core-shell composites depend heavily on the materials constituting both the core and the shell parts. These compounds offer superiorities in terms of dimension, optical properties, electronic characteristics, etc. so that they have found various applications in photovoltaic cells, optical sensors, biological systems, and catalysis technology etc.

Metallic core-shell catalysts composed of, one metal at the center, i.e., the core, and the second is at the surface, or the shell, provide distinctive properties, often a better reactivity, because the core metal particle could modify the lattice strain of the shell metal, which results in a shift of the electronic band structure of the shell metal.

Core shell nanoparticles increases the quantum by passivating the surface trap states.The shell provides protection against environmental changes, photo-oxidative degradation, and provides another route for modularity. Precise control of the size, shape, and composition of both the core and the shell enable the emission wavelength to be tuned over a wider range of wavelengths than with either individual semiconductor.

Core –shell Nanoparticles widely used for the improvement of semiconductor efficiency, information storage, optoelectronics, catalysis, quantum dots, optical bioimaging, biological labeling, etc. Furthermore, of the different types of inorganic/inorganic nanoparticles, it can be seenthat, in general, boththe cores and shells are made of metal, metal oxide, other inorganic compounds, or silica.