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Quantized CdS crystallite-doped tetraethylorthosilicate (TEOS) silica xerogels are prepared by the sol-gel method. In this method, cadmium acetate [Cd(CH3COO)22H2O]-doped TEOS alcogel is formed by the hydrolysis and polycondensation of ethanolic TEOS in the presence of hydrochloric acid (HCl) and ammonium hydroxide (NH4OH) catalysts and Cd(CH3COO)2.2H2O. The CdS crystallites are formed in the alcogel by the reaction of Cd(CH3COO)2.2H2O present in the gel and methanolic sodium sulfide (Na2S), which is added over the alcogel. The effect of CdS/TEOS, EtOH/TEOS, S/Cd molar ratios, and temperature on the optical properties and CdS crystallite sizes in the xerogels are studied. A blue shift is observed in optical absorption spectra by decreasing the CdS/TEOS molar ratio from 2 × 10-2 to 1 × 10-4. It is observed that the crystallite size is increased from 1.6 to 3.4 nm by increasing the EtOH/TEOS molar ratio from 2 to 20, respectively, for a constant CdS/TEOS molar ratio of 5 × 10-4. Emission spectra of xerogels are measured and found that the emission peak maxima shifted toward lower energies (higher wavelengths) by increasing the CdS/TEOS molar ratio in the xerogels. It is known from the X-ray diffraction (XRD) measurements of CdS-doped xerogels that the CdS crystallite structure in the xerogels is hexagonal wurtzite. The crystallite sizes were calculated from the XRD patterns and tight bonding calculations. There is a significant change in the color and size of CdS crystallite in the xerogels with a variation in temperature from 200 to 400°C.
| Authors: | N. N. Parvathy, G. M. Pajonk, A. Venkateswara Rao | |
| Journal: | Journal of Materials Synthesis and Processing | |
| Year: | 2004 | |
| DOI: | 10.1023/A:1021897409664 | |
| Publication date: | 03-Nov-2004 |
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