Optical and Magnetic Properties of Undoped and Transition Metals Doped CdSe Quantum Dots.

Semiconductor Quantum Dots (QDs) have been a topic of intense interest over the last few decades due to their size dependent optical properties and applications in various fields such as Optoelectronics, Photovoltaics, Bio-imaging etc. Currently, magnetic properties of doped semiconductor nanomaterials have received considerable attention due to their unique dopant dependent magnetic properties and possibility to use them as a spintronics material. However, the subject has become debatable as the origin of ferromagnetism in doped semiconductors materials was questionable. The role of possible extrinsic and/or intrinsic in the material is not yet fully understood. The work which will be presented here is distributed into two related parts. In the first part, the optical and magnetic properties of zincblende CdSe QDs, of different sizes, have been discussed. In order to synthesize different sizes of CdSe NPs we have used both aqueous (thiol capped) as well as nonaqueous (olive oil/oleic acid capped) chemical synthesis route. The particle size for CdSe NPs was varied from 1.5±0.1 nm to 12±0.1 nm. Room temperature ferromagnetism (RTFM) was observed in various sizes of CdSe QDs. The saturation magnetization is strongly dependent on the particle size and defects present in CdSe Quantum Dots. In addition, the synthesized QDs show size dependent photoluminescence tuning in the entire visible electromagnetic spectrum. In the second part, the effect of different dopants (Cu, Fe and Cu:Mn) and doping concentration on optical and magnetic properties of CdSe QDs has been discussed. In case of copper doping, copper concentration dependent photoluminescence tuning in the entire visible electromagnetic spectrum is observed. While in case of iron doping in a given size distribution of CdSe QDs, photoluminescence is strongly dominated by size. In smaller particles photoluminescence is dominated by Fe3+ excited state to the Fe3+ ground state emission and in larger particles, excitonic as well as defect luminescence dominates. In case of manganese doped and (Cu and Mn) codoped CdSe QDs, photoluminescence is dominated by Mn2+ mission while increasing manganese concentration in CdSe and CdSe:Cu QDs respectively. It is observed that saturation magnetization is strongly dependent on dopants (Cu, Fe and Cu:Mn) and doping concentration. To explain the phenomenon, systematic analysis of samples using a variety of physico-chemical techniques has been performed.