Red Shift Of Fluorescence Band Research Articles

Preparation and optical properties of blue-emitting colloidal CdS nanocrystallines by the solvothermal process using poly (ethylene oxide) as the stabilizer

Blue-emitting colloidal CdS nanocrystals have been synthesized through the solvothermal reaction of cadmium acetate and thiourea in N,N-dimethylformamide using poly(ethylene oxide; PEO) as the stabilizing polymer. The as-prepared CdS colloids were stable at ambient conditions for several weeks. The PEO-stabilized CdS colloids showed a narrow fluorescence band with the maximum at about 420 nm and thus emitting blue fluorescence under the ultraviolet (UV) lamp. A common red shift of fluorescence band is not detected for the prepared CdS colloids in the study, indicating that PEO-stabilized CdS NCs possess few crystalline defects on their surface. In addition, transmission electron microscope micrographs reveal that the sizes of CdS NCs are between 4.4 to 5.4 nm with small standard deviations from 0.5 to 0.7 nm. The particle growth kinetics was studied by monitoring UV-visible absorption onsets versus the reaction time and was found to nearly follow the Lifshitz–Slyozov–Wagner theory for the Ostwald ripening mechanism.

Study of self-aggregation of coal derived asphaltene in organic solvents: A fluorescence approach

Abstract Fluorescence spectra of coal derived asphaltenes sourced from Barari coke plant situated at Dhanbad, India, have been studied as a function of concentration in benzene, toluene and carbon tetrachloride with an eye to study the self-aggregation of the solute. Aggregation has been found to be a gradual process and the concentration characterizing onset of aggregation process coincide for the solvents. The critical aggregation constants (CAC) appear to be ca 90–100 and 180–200 for all the solvents. A small red shift of fluorescence band is observed when traces of water (∼0.05%, v/v) are present in carbon tetrachloride solution.