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 usin g ethanolic tetraethylorthosilicate [Si(OC2H5)(4)] and Cd(CH3COO)(2) . 2H(2)O in the presence of HCl and NH4OH hydrolysis and condensation c atalysts. 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 fl ow 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 monodisperse d 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 xer ogels 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 crysta llite structure was found to be hexagonal wurtzite from the XRD spectr a of the sample and the CdS crystallite size in the silica matrix vari ed from 0.9 to 6 nm with the variation of CBS wt% 0.01 to 3, respectiv ely. 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 s ample. (C) 1998 Acta Metallurgica Inc.