Study of photophysical properties of doped/undoped semiconductor and metal nanoparticles and their heterostructures

Colloidal nanocrystals have been the centre of attraction of materials science research due to the ability of tailoring their properties with size, shape or composition of the same, in comparison to their bulk counterparts. Among these, mostly studied are binary and alloyed binary nanocrystals comprising of group II-VI and III-V materials. CdSe has been the work horse in this area with the emission covering the entire visible region. But the intrinsic toxicity along with the problem of re-absorption and self quenching in many of these binary materials limit their applications in several fields. To overcome these issues, insertion of intra-band gap states has been proved to be the most efficient way. The frontiers in this field are doped semiconductors where an external impurity atom is introduced which creates a trap state that takes part in the radiative recombination process and the ternary nanocrystals, where substituitional defect takes part in the radiative recombination process. These semiconductor nanocrystals have been applied to many different technological areas including biological labelling and diagnostics, light-emitting diodes, electroluminescent devices, photovoltaic devices, lasers and single-electron transistors. Apart from changing the size and composition of the nanocrystals, creation of novel nanostructures and the mechanism of crystal growth have been investigated driven both by the excitement of understanding new science and also their potential applications in specific cases of device based technologies and catalysis etc. With the proper manipulation of reaction parameters, e.g., precursors, temperature and stabilizing agents, many structurally unprecedented motifs have been discovered including polyhedrons, rods and wires, plates and prisms, and other advanced shapes such as branched rods, stars and multipods etc. Another important research direction in nanomaterials synthesis has been the expansion from single-component nanoparticles to hybrid nanostructures with discrete domains of different materials arranged in a controlled fashion, be it a semiconductor-semiconductor, metal-metal or semiconductor-metal.35-36 The attraction of multicomponent nanostructures is that multiple functions can be integrated into one system for specific applications. Moreover, the interactions between nanoscale-spaced components can greatly improve the overall application performance of the system and even generate new synergetic properties. For example, Au epitaxially connected with the semiconductors show improved charge separation and enhanced light absorption of the semiconductor part, as well as can alter the luminescence behavior of semiconductors. Both of these increase the photocatalytic and light-harvesting efficiencies of semiconductors. Several semiconductor-semiconductor heterostructures have also been reported.The research was carried out under the supervision of Prof. Narayan Pradhan of the Materials Science division under SMS [School of Materials Sciences]The research was conducted under IACS fellowship and DST research garn