A new route for preparing CdX (X = S, Se, Te, S+Se) nanocrystallites
dispersed in a sodium borosilicate glass matrix from a hydrogel is proposed.
Chalcogenizing complexing molecules - for instance a mixture of
NH4SCN + H2SeO3 - introduced in the
starting solution allowed an in situ crystallite
preparation concomitant to gel densification. Prevention of crystallite
oxidation is thus obtained. Moreover, coalescence is minimized because of
the low gel-glass transition temperature. Low temperature absorption spectra
have been interpreted in terms of exciton and electron-hole confinements,
accounting for both an intrinsic broadening of energy states inside each
nanocrystal and a Gaussian size distribution. Crystallite sizes and size
dispersion can be adjusted by changing the initial Cd concentration. The
crystallinity of the nanoparticles without change in dispersion is strongly
improved by thermal treatment above the Tg of the glass
matrix.