Nucleation of Precipitates of ZnS and (Zn, Cd)S for Phosphor Synthesis

Abstract

Monodisperse particles of and (Zn, Cd)S were grown by precipitation from an acidified water solution. We have examined these materials by analytical electron microscopy. The typical spherical precipitates have diameters ≈ 5 μm; in addition, the volume fraction of voids is about 35%. At high magnifications, , using SEM, a precipitate resembles a ball of tangled string. Thinned precipitates were examined by STEM and TEM. A central plane of (Zn, Cd)S shows a central region with a large concentration of ; this region has a diameter ≈ 2.3 μm. The diameter of the outer region is about 4.0 μm and contains mostly . This happens because the solubility product of is smaller than that of by several orders of magnitude. Suitably thinned samples of both and (Zn, Cd)S show the development of small holes, which are found predominantly at the center of the precipitates; the precipitates are thought to nucleate on bubbles, (e.g., or air), which are revealed as holes upon ion‐thinning. The microstructure shows lamellae, , arrayed in spoke‐like fashion about the center of the precipitate. It is likely that these crystals represent a new example of spherulitic growth.