INOR 174 |
| II-VI group colloidal semiconductor nanocrystals, showing size-dependent optical properties in visible range, have been extensively investigated in recent years for the application including light emitting device (LED), biological fluorescent labels and lasers. However, the preparation of high quality blue emitting semiconductor nanocrystal is difficult because crystal size should decrease below ~2nm to emit blue light and the resulting small crystal has unstable surface trap to decrease the quantum efficiency. Therefore, proper treatment of the nanocrystal surface to reduce defect sites is needed to achieve high quantum yield. In this work, highly blue luminescent nanocrystals were prepared by simple surface treatment at room temperature with reducing agent like NaBH4. The quantum efficiency of CdS nanocrystal was remarkably enhanced up to 75% at blue region, about 50 times improvement after surface treatment maintaining original photoluminescence peak position and narrow line width. The TGA and XPS data revealed that some of the surfactants on the nanocrystal surface were removed by reacting with NaBH4 and that the exposed cadmium on the surface was converted to cadmium oxide under air condition. The oxide layer functioned as a passivation layer on the CdS surface and donated more electron density toward the inside of the CdS core to enhance exciton recombination. The surface treatment was generally effective in improving the quantum efficiency of II-VI compound semiconductors including CdS, CdSe and CdTe and other mixture type nano-sized materials. We also prepared highly luminescent multi-component semiconductor nanocrystals exhibiting tunable optical property in blue region by control of reaction temperature, time and precursor concentration. The resulting nanocrystals were embedded in the light emitting diode as an active material, and the external quantum efficiency of the pure nanocrystal electroluminescence was 1.5Cd/A at 470nm. The detailed results will be further discussed in the presentation. |
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Nanoscience: Synthesis
7:00 PM-9:00 PM, Sunday, 13 March 2005 Convention Center -- Hall D, Poster
Division of Inorganic Chemistry |