Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5403826 | Journal of Luminescence | 2008 | 9 Pages |
Abstract
CdTe nanocrystals were grown from commercially available RG850 Schott filter glass by two-step heat-treatment process which almost doubles the particle to matrix volume fraction. A calculation shows that a quantized-state effective mass model in the strong confinement regime might be used to deduce the average radius for the nanocrystals larger than 2Â nm in radius from the energetic position of the first exciton peak in optical absorption spectrum. Size-induced shift of â¼360Â meV in the first exciton peak position was observed. The steady state photoluminescence spectra exhibit a broad band red shifted relative to the first exciton band, which indicates the existence of shallow trap states. The non-linear optical properties of CdTe nanocrystals were studied by room temperature resonant photoabsorption spectroscopy. The differential absorption spectra had three-lobed structure whose size-dependent evolution was explained by bleaching of the absorption, red shift and broadening in the Gaussian absorption band used to fit the first exciton peak. A maximum red shift of 2.32Â meV for the average nanocrystal radius of 4.65Â nm was estimated by fitting the photomodulation spectra with a combination of first and second derivative Gaussian absorption bands. We presume that the red shift is induced by the electric field of trapped charges in surface states. Internal electric field strengths of 23 and 65Â kV/cm were predicted for the average nanocrystal radii of 3.95 and 4.65Â nm, respectively, with the help of second-order perturbation theory in the strong confinement limit.
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Authors
M.H. Yükselici, Ã. Allahverdi,