Cadmium Selenide Based Core-Shell Quantum Dots for Biosensing and Imaging Applications

The overall focus of the thesis involves the synthesis and characterization of CdSe QDs overcoated with shell materials for various biological and chemical sensing applications. Second chapter deals with the synthesis and characterization of CdSe and CdSe/ZnS core shell QDs. The primary attention of this work is to develop a simple method based on photoinduced charge transfer to optimize the shell thickness. Synthesis of water soluble CdSe QDs, their cytotoxicity analysis and investigation of nonlinear optical properties form the subject of third chapter. Final chapter deals with development of QD based sensor systems for the selective detection of biologically and environmentally important analytes from aqueous media

An approach for optimizing the shell thickness of core-shell quantum dots using photoinduced charge transfer

Photoinduced charge-transfer dynamics between CdSe quantum dots (QDs) possessing varying monolayers of ZnS and hole scavengers such as phenothiazine (PT) and N-methylphenothiazine (NMPT) were investigated for optimizing the shell thickness of core-shell quantum dots. Spectroscopic investigations indicate that phenothiazine binds onto the surface of bare CdSe QDs, resulting in the photoluminescence quenching, and two monolayers of ZnS prevent the electron-transfer process. Methodologies presented here can provide quantitative information on the optimum shell thickness of core-shell QDs, which can suppress the undesired electron transfer and provide maximum luminescence yield

Solvent polarity and nanoscale morphology in bulk heterojunction organic solar cells: A case study

Organic bulk heterojunction solar cells were fabricated under identical experimental conditions, except by varying the solvent polarity used for spin coating the active layer components and their performance was evaluated systematically. Results showed that presence of nitrobenzene-chlorobenzene composition governs the morphology of active layer formed, which is due to the tuning of solvent polarity as well as the resulting solubility of the P3HT:PCBM blend. Trace amount of nitrobenzene favoured the formation of better organised P3HT domains, as evident from conductive AFM, tapping mode AFM and surface, and cross-sectional SEM analysis. The higher interfacial surface area thus generated produced cells with high efficiency. But, an increase in the nitrobenzene composition leads to a decrease in cell performance, which is due to the formation of an active layer with larger size polymer domain networks with poor charge separation possibility. (C) 2014 AIP Publishing LLC