Preparation and optical properties of ZnS-microcrystals deposited in silica gels

ZnO doped silica gels were synthesized by the hydrolysis and condensation of complex solution tetraethyl orthosilicate (TEOS) and zinc acetate (Zn(Ac)2) and heating at 500°C in the air. For conversion to ZnS doped gels, they were exposed to H2S gas at appropriate temperatures. The crystal size of ZnS determined by the width of X-ray diffraction pattern and direct transmission electron micrograph (TEM) grows from 1 to 4 nm with an increase of reaction temperature with H2S gas. The edge energies of optical absorption shifted to higher energy side compared with that of bulk crystal and reciprocally increased in proportional to the square of the crystal size. The peak energy of fluorescence spectra also shifted to lower energy side with an increase of reaction temperature exposing to the H2S gas. Thus, the quantum size effect could be found for ZnS microcrystals in the gels.