Synthesis of various size CdS nanocrystals in porous silica matrix and their spectral and physical properties

Cadmium ion doped silica xerogels were prepared by sol-gel method using ethanolic tetraethylorthosilicate [Si(OC2H5)(4)] and Cd(CH3COO)(2) . 2H(2)O in the presence of HCl and NH4OH hydrolysis and condensation catalysts. CdS crystallites were formed in the xerogels by passing H2S gas over the cadmium ion doped materials. The effect of H2S amount and temperature on the distribution of CdS crystallites-in the sample was studied by varying the reaction time from 15 min. to 3 hours, with flow rate of 1 bar H2S/hour and temperature from 50 to 500 degrees C for constant Cd/TEOS molar ratio of 0.004. It was found that monodispersed CdS crystallites were obtained for a minimum reaction time-of 1 hour anal temperature of 150 degrees C. A quantum size effect was observed in the absorption and fluoresence spectra of the CdS doped silica xerogels with from 3 to 0.01 wt.% CdS. The density and refractive indices were measured and it was found that there was an increase in density from 1.875 to 1.908 gm/cm(3) and refractive index from 1.450 to 1.523 with variation of CdS wt% from 0.01 to 3, respectively. The CdS crystallite structure was found to be hexagonal wurtzite from the XRD spectra of the sample and the CdS crystallite size in the silica matrix varied from 0.9 to 6 nm with the variation of CBS wt% 0.01 to 3, respectively. There was an additional peak at 265 cm(-1) other than SiO2 matrix bond peaks, which corresponds to Cd-S bond in the IR spectra of the sample. (C) 1998 Acta Metallurgica Inc.