Synthesis and Characterization of CdSe/CdS Core-Shell and CdSe/CdS Composites
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291 Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
EXPERIMENTAL Chemicals Tri-n-octylphosphine oxide (TOPO), tri-n-octylphosphine (TOP), n-methylhexylamine, and carbon disulfide were purchased from Aldrich Chemical Company Ltd and methanol and toluene from BDH. TOPO was purified by vacuum distillation at ca. 250' C ( 0.1 torr). The solvents used for air sensitive chemistry were distilled , deoxygenated under a nitrogen flow and stored over molecular sieves (type 4 A, BDH) before use. Instrumentation Ultra violet/Visible (UV/Vis) Absorption Spectroscopy: A Philips PU 8710 spectrophotometer was used to carry out the optical measurements of the semiconductor
nanoparticles. The samples were placed in silica cuvettes ( 1 cm path length). Photoluminescence Spectroscopy: A Spex FluoroMax instrument with a xenon lamp (150W) and a 152 P photomultiplier tube as a detector was used to measure the photoluminescence of the particles. Good spectral data was recorded with the slits set at 2mm and an integration time of 1 second. The samples were quantitatively prepared by dissolving 25 mg in 10 ml toluene. The samples were placed in quartz cuvettes (1 cm path length) used as blank for all measurements. The wavelength of excitation was set at a lower value than onset of absorption of a typical sample. X-Ray Diffraction (XRD): X- Ray diffraction patterns were measured using a Philips PW 1700 series automated powder diffractometer using Cu- K( radiation at 40kV/4OmA with a secondary graphite crystal monochromator. Samples were prepared on glass slides (5 cm). A concentrated toluene solution was slowly evaporated at room temperature on a glass slide to obtain a sample for analysis. Electron microscopy: A Joel 2000 FX MK I operated at 200KV electron microscope' with an Oxford Instrument AN 10000 EDS Analyser was used for the conventional TEM (transmission electron microscopy) images. Selected area electron diffraction (SAED) patterns were obtained using a JEOL 2000FX MK 2 electron microscope operated at 200kV. The samples for TEM and SAED were prepared by placing a drop of a dilute solution of sample in toluene on a copper grid (400 mesh, agar). The excess solvent was wicked away with a paper tip and completely dried at room temperature. Synthesis All experiments were carried out by using dry solvents and standard Schlenck techniques. Glassware was dried in the oven before use. (i) Preparation of CdSe/CdS core-shell nanoparticles In a typical synthesis, [Cd(Se 2CNMe(Hex)) 2] (0.8 g) was dissolved in tri-noctylphosphine (TOP) (15 ml). This solution was then injected into hot (250' C) tri-noctylphosphine oxide (TOPO) (20 g) and kept at this temperature for 30 minutes. After this time a small amount of sample was syringed out of the reaction mixture for characterization as the CdSe nanoparticles. Then a solution of [Cd(S 2CNMe(Hex)) 2 ] (0.5 g) in TOP (10 ml) was injected into the deep red reaction mixture. The reaction was allowed to proceeded for a further 30 minutes and the resulting solution was cooled to ca.
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